Dissertations / Theses: 'Dieback'

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Evans, David Paul. "Biological indicators of forest dieback." Thesis, University of South Wales, 1992. https://pure.southwales.ac.uk/en/studentthesis/biological-indicators-of-forest-dieback(514886c2-00a0-4280-aca2-a500e3e794cb).html.

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This study involved the determinations of the foliar levels of chlorophyll a and b and metal levels in the year 1, year 2 and year 3 needles of Sitka spruce. A survey was made of nineteen sites in the Afan 1 forest in South Wales. The results obtained indicates that there are two distinct types of site, namely good growth sites and poor growth sites. The poor growth sites were found to be at higher elevations. Further analyses of the results show that there is possibly an increased loss of nutrients from the trees at the poor growth sites. This may be due to increased pollution that may be present at the higher elevations. In 1987 a survey was made of the one year old epicormic tissues that were compared with the normal tissues at the 19 sites of the Afan 1 Forest There were no statistically significant differences in the levels of the chlorophylls or in any of the metals that were looked at. At the Afan 1 Forest there are observed pairs of trees that are growing quite close together, but they exhibit quite a marked difference in growth. One of the pair shows vigorous healthy growth, whilst the other is stunted and shows symptoms of decline. One such pair is found at Site 15. They are of the same age and from the same seed stock. It was found that over an eight month period, the stronger growing of the pair had significantly higher levels of chlorophyll a and b, potassium, calcium and magnesium. This may indicate increased leaching and foliar damage from the poorer growing of the pair. Three more pairs of trees together with their grafts were examined from sites' 1,5 and 6, for their levels of peroxidase enzymes. Peroxidase has been used to determine possible genetic differences in cultivars. The work yielded very little useful information. The SCOR-UNESCO equations have been widely used as a means of determining chlorophyll levels from plant extracts. A multivariate calibration method was used in conjunction with HPLC to determine the accuracy of these equations for determining the levels of chlorophyll and b. The results show revealed that the equations appear to be underestimating the chlorophyll a levels. Leading on from the HPLC work, a novel method for the separating a mixture of chlorophyll a and b was developed using packed column SFC. The method appears to be quite promising with its better resolution and faster analysis times as compared to FIPLC methods. Sitka spruce seedlings were grown in COIR (coconut husk) and were used in and were used in a central composite design to determine the effects of cadmium and copper, both singly and in combination would have upon their growth. Response surface methodology was used to determine the effects and it was found from the experiment that high levels of cadmium appeared to have an effect upon the elongation of the needles of the new shoots.

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Nobrega, Caroline Correa. "Amazon forest dieback: assessing vulnerabilities and threats." Universidade Federal de Goiás, 2016. http://repositorio.bc.ufg.br/tede/handle/tede/5873.

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In recent years, it is increasing evidences about Amazon vunerability due to land use and climate changes. Because of a positive feedback system, in which impacts intensify other impacts, some models project to the end of the century a replacement of the Amazon forest by savanna formations or semi-arid (forest dieback). Several evidence has indicated a high vulnerability of the Amazon to global climate change and local environmental impacts triggered by human activities (eg conversion to agricultural areas, construction of roads and burns). However, they are still deeply unknown the general mechanisms and standards about how these impacts affect the forest. In this thesis, I developed works that aim contribute to discussions of the subject. In each chapter, I will consider a threat that is contributing to the degradation of the Amazon. Each of the three threats discussed in the following chapters are often cited as important drivers of forest dieback. In the first chapter I evaluated the impact of forest fires at different levels of diversity of trees in a forest area next to the Amazon-Cerrado transition. Our results suggest that communities of trees in burned areas are losing more phylogenetic and functional diversity per unit of species than in unburned areas. My results indicate the existence of selection of species based on phylogenetic and functional characteristics, representing a major force of change and impoverishment (functional and phylogenetically) of these communities. In the second chapter, using high resolution images (LiDAR and hyperspectral), I evaluated the impact of a intense drought in forest areas near Madre de Dios, Peru. Thus, my results support the idea that changes in regional climate may change the structure and function of the forest. In the third chapter, I evaluated how the construction of roads in the Brazilian Amazon has contributed to deforestation in an important group of protected areas of the Amazon: the Indigenous Lands. Based on the analysis of observed impacts, I propose the establishment of buffer zones (buffers) around these reserves to reduce the negative impacts of road construction planned to be built.
Nos últimos anos, tem surgido cada vez mais evidências que a Amazônia pode estar ameaçada em decorrências das mudanças regionais no clima e no uso do solo. Por causa de um sistema de retroalimentação positivo, em que impactos intensificam outros impactos, alguns modelos projetam para o final do século uma substituição da floresta amazônica por formações tipo savana ou semiáridas (forest dieback). Diversas evidências têm indicado uma alta vulnerabilidade da Amazônia às mudanças climáticas globais e aos impactos ambientais locais desencadeados por atividades humanas (e.g. conversão de áreas para agropecuária, construção de estradas e queimadas). Entretanto, são ainda profundamente desconhecidos os mecanismos e padrões gerais de como esses impactos afetam a floresta. Nesta tese, desenvolvi trabalhos que têm como objetivo contribuir para as discussões do tema. Em cada capítulo, abordarei uma ameaça que, de alguma forma, está contribuindo para a degradação da Amazônia. Cada uma das três ameaças discutidas nos próximos capítulos são, frequentemente, apontadas como importantes propulsores de forest dieback. No primeiro capítulo avaliei o impacto de incêndios florestais em diferentes níveis de diversidade de árvores de uma área florestal próxima à transição Amazônia-Cerrado. Nossos resultados sugerem que as comunidades de árvores das áreas queimadas estão perdendo mais diversidade filogenética e funcional por unidade de espécie do que nas áreas não queimadas. Nossos resultados indicam a existência de seleção de espécies com base em características filogenéticas e funcionais, que representam uma importante força de mudança e de empobrecimento (funcional e filogeneticamente) dessas comunidades. No segundo capítulo, usando imagens de alta resolução (LiDAR e hiperespectral), eu avaliei o impacto de um período de seca em áreas florestais próximas a Madre de Dios, Peru. Nossos resultados dão suporte a hipótese de que mudanças no clima regional modificam a estrutura e função da floresta. No terceiro capítulo, eu avaliarei de que forma a construção de estradas na Amazônia brasileira tem contribuído para o desmatamento que incide em um importante grupo de áreas protegidas da Amazônia: as Terras Indígenas. Com base na análise dos impactos observados, nós propomos o estabelecimento de zonas de amortecimento (buffers) em torno dessas reservas para reduzir os impactos negativos da construção de estradas planejadas para serem construídas.

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Hill, Louise. "Ecological impacts of ash dieback in Great Britain." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:941ee684-798b-47b6-ae51-64baeb5f821e.

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Ash dieback is a severe disease of ash trees (Fraxinus spp.), caused by the invasive fungus Hymenoscyphus fraxineus. In its native East Asia, H. fraxineus is a harmless endophyte, but since its accidental import into Europe in the early 1990s it has infected over 90% of ash trees in some areas, with long-term mortality sometimes exceeding 90%. The disease was discovered in Great Britain in 2012, and has since spread rapidly. This thesis investigates some of the possible impacts on biodiversity, ecosystem functioning, and society, and in doing so identifies ways to alleviate some impacts. Britain has only 13% tree cover (among the lowest in Europe), so may be particularly vulnerable to ash loss. Better understanding of the effects and how to minimise them is critical to deliver an evidence-based response. First, we investigated impacts in woodlands by experimentally killing woodland ash trees by ring-barking. We found no short-term effect of ash loss on ground flora or earthworm communities, or on the regeneration or growth of other woody species. Observational evidence suggested that remaining canopy trees rapidly filled gaps left by ash, perhaps contributing to stability. Our woodlands appeared to be remarkably resilient to ash loss, although there may be long-term effects or impacts on other species that this experiment failed to observe. To investigate broader-scale impacts, we required high-quality abundance maps for ash and other trees across Britain. Using species distribution modelling and random forest regression, we developed a protocol to produce abundance maps from readily available data. We tested the predictive power of the resulting maps using cross validation. Our maps are the best available for abundance of British tree species, and will be useful across a wide range of disciplines. We then used them to model ecosystem vulnerability to ash loss, based on the abundance of ash and other tree species, and their ecological trait similarity. We identified areas at risk of the largest impacts, and produced guidance for positive management actions to minimise ecological change. Lastly, we investigated the financial impacts of ash dieback, estimating the total cost to Britain at £9.2 billion. This figure is many times larger than the value of lost trade if biosecurity were improved to prevent future invasions, questioning the validity of financial arguments against biosecurity. We also found that loss of ecosystem services accounted for less than a third of the total cost, suggesting that ecosystem service assessments may miss a large proportion of the true cost of biodiversity loss. Overall, we found that some impacts may be less than expected, such as local effects on woodland ground flora, and others, such as the economic cost, may be much larger than expected. However, the resilience of ecosystems to a major shock such as loss of a common species, and actions to mitigate the impacts, depend on having a diversity of other trees present. The ash dieback outbreak highlights the importance of preventing other severe pests and diseases of trees from being introduced; something that has been increasing exponentially, largely due to international trade in trees. This thesis provides further firm evidence that there is an ecological and social imperative to halt this trend.

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Lardner, Richard. "Early diagnosis and detection of Eutypa dieback of grapevines." Title page, table of contents and abstract only, 2003. http://hdl.handle.net/2440/37969.

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Eutypa dieback of grapevines, caused by Eutypa lata, is a major cause of reduced longevity in vineyards worldwide. The fungus grows in the woody tissue of infected vines, producing translocatable toxins that cause foliar symptoms of the disease. By the time foliar symptoms are evident the pathogen may have become well established in the vine. One aim of this study was to develop DNA markers to allow rapid reliable identification of E. lata and to detect the pathogen in infected wood. The second aim was to analyse secondary metabolite production by E. lata in order to gain information on the compounds responsible for the foliar symptoms of the disease and to identify metabolites which could be used as markers to detect the early stages of the disease prior to the expression of foliar symptoms. In addition, genetic variation of the pathogen was assessed using RFLP and RAPD analysis. Two techniques were used to develop DNA markers; first, SCAR markers derived from RAPD fragments were developed and, second, an E. lata genomic DNA library was constructed, from which DNA fragments specific to E. lata were identified. These markers were used in either PCR- or Southern hybridisation-based assays to detect the pathogen in infected wood. PCR-based detection of the pathogen in infected wood was prone to inhibition by phenolic compounds, however, Southern hybridisation techniques were capable of detecting E. lata in wood. Genetic variation among 38 isolates of E. lata was assessed using six randomly selected clones from the genomic DNA library. A subset of 11 isolates was subjected to RAPD analysis using 10 random primers. Considerable genetic diversity, in terms of RFLP and RAPD profiles, was observed among isolates. There was no apparent correlation between grouping of isolates following neighbour joining analysis and either host species or geographic origin of isolates. The RAPD and RFLP profiles of two isolates differed significantly from the majority of the other isolates. These isolates, which were morphologically similar to all other isolates, were subsequently found not to be E. lata. Secondary metabolite production of 11 isolates was analysed by HPLC following growth on a range of media. A wider range of secondary metabolites was detected in E. lata than has previously been reported. Two of the secondary metabolites, eutypine and an unidentified compound with a retention time of 19.6 min, were produced by eight of nine isolates of E. lata. Neither of the non-E. lata isolates produced these compounds. It was concluded that the remaining isolate of E. lata may have lost the ability to produce these compounds following storage. Whilst a wider range of isolates needs to be screened before a candidate marker can be selected, these results suggest that certain compounds are present in the majority of E. lata isolates and, hence, may prove suitable markers for the detection of the pathogen prior to the expression of foliar symptoms. The molecular probes developed in this study will allow the rapid and reliable identification and detection of E. lata in grapevine cane or wood. These probes also have the potential to be used as a research tool to gather information on the epidemiology of the disease and to assess the efficacy of potential control agents against E. lata. Suitable control measures could then be applied to vines which have been shown by the use of chemical markers to have latent infection. Used in combination, therefore, the DNA and biochemical markers could facilitate improved management of eutypa dieback.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture and Wine, 2003.

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Raiter, Keren. "Bush tucker and dieback : the threat of dieback caused by Phytophthora cinnamomi to plants of significance to Noongar people of Western Australia's south coast." Thesis, Raiter, Keren (2005) Bush tucker and dieback : the threat of dieback caused by Phytophthora cinnamomi to plants of significance to Noongar people of Western Australia's south coast. Honours thesis, Murdoch University, 2005. https://researchrepository.murdoch.edu.au/id/eprint/32600/.

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Rolshausen, Philippe. "Biology and control of Eutypa dieback of grapevine in California /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.

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Singh, Gurpreet. "Identification of Quantitative Trait Loci (QTL) associated with resistance to Vascular Streak Dieback disease of cacao." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/29254.

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Vascular-Streak Dieback (VSD) disease of cacao, caused by the fungus Ceratobasidium theobromae, has devastating impacts on cacao production in southeast Asia and Oceania. This study aimed to identify genomic regions associated with resistance to VSD using a population derived from a cross between the cocoa genotypes S1 (VSD resistant) and CCN51 (VSD susceptible). QTL analysis was performed using a genetic linkage map constructed with 8,698 DArT markers and 1,470 SNP markers. Two QTL were detected, one on linkage group 8 and the other on linkage group 9. The QTL on linkage group 8 explained 15-16% of the phenotypic variation while the QTL on linkage group 9 explained 16-18% of the phenotypic variation. Five polymorphic microsatellite (SSR) markers were identified within the QTL regions. SSR markers showed clear polymorphism among the VSD resistant and susceptible lines in the two populations, S1 x CCN51 and CCN51 x M07. These results suggest that these markers could be closely associated with VSD resistance and therefore used in marker-assisted selection for cacao breeding programs in response to VSD disease. Further, genomes of the S1 and CCN51 genotypes were sequenced using paired end short reads. Both S1 and CCN51 whole genome sequencing generated 383 and 367 million clean reads, respectively, and 93% of reads from both S1 and CCN51 mapped to the reference genome Matina 1-6. Alignment to the reference genome enabled the detection of 1.87 million polymorphic SNVs/Indels and 8,363 polymorphic structural variants (SVs) among the two genomes. The resequencing of the genomes of cacao genotypes S1 and CCN51 provides a valuable resource to narrow the search for candidate genes that underlie VSD resistance.

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Cujec, Thomas Peter. "Incidence, etiology and epidemiology of stonefruit dieback in the Okanagan Valley." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/27865.

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A Cytospora species isolated from infected tissues and sporulating stromata on diseased trees caused typical dieback symptoms when inoculated into Prunus species and was identified as the primary cause of stonefruit dieback in the Okanagan. Based on the morphology of the stromata, spore dimensions, and colony growth and color on malt extract agar, the fungus was identified as C. leucostoma (Sacc). After including the number of trees removed during the winter of 1985-86 and 1986-87 because of Cytospora sp., an average of 14.8% of the trees in 17 stonefruit orchards were affected by dieback from September 1985 to September 1987. The incidence of Cytospora sp. in the individual blocks ranged from 3.0-56.9%. In 11 of the 17 orchards surveyed in 1986 and resurveyed in 1987, dieback symptoms were evident on trees which had been symptomless in 1986. The percent of newly infected trees in these 11 blocks ranged from 0.4-8.8% and averaged 2.9%. The majority of sporulating Cytospora sp. infections were found on the scaffold limbs (69%) or trunks (28%) of infected trees. Pruning wounds (65%), rather than winter injury (25%), were the major infection courts. Fall and spring inoculations of a spore suspension (10³ spores/ml) of either a peach isolate (P8-19) to peach, or a cherry isolate (C9-23) to cherry revealed that intraspecies spread of the disease can occur at any time of the year. Although spring spore inoculations of the peach isolate to cherry or the cherry isolate to peach resulted in significantly (P = 0.05) more infections than the control treatments, identical fall inoculations did not. This suggests that spread of Cytospora sp. between cherry and peach is most likely to occur in the spring. The effect of temperature on spore germination and mycelial growth of Cytospora sp. in vitro was isolate-dependent. The minimum lag period for Cytospora sp. spore germination occurred at 27° C. Spores germinated at temperatures as low as 10° C, and remained viable even after exposure to -18° C for 1 week. The temperature optima for the in vitro growth of most stonefruit isolates in this study was 20-23° C. Viable Cytospora sp. spores were washed from infected trees (10⁵-10⁶ spores/ml) and adjacent healthy trees (10⁴ spores/ml) in mid-December and collected in funnel traps after the first rain the following spring (late April). Under Okanagan conditions, infection of fresh pruning wounds made in the spring can occur either by spores which overwintered on infected trees and were dispersed by spring rains, or by spores dispersed by fall rains to healthy trees on which they overwintered and infected following pruning. Benomyl (1 g a.i./L), dichlone (1 g a.i./L), flusilazole (0.01 g a.i./L) and ziram (5 g a.i./L) applied as water sprays did not significantly (P = 0.1) reduce the percent infection compared to the unprotected, inoculated controls. Of eight fungicide-pruning paste mixtures, only benomyl added to either Heal 'n' Seal or linseed oil significantly (P = 0.1) reduced the number of cankers which developed compared to the untreated control.
Land and Food Systems, Faculty of
Graduate

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Reich, Richard William. "Causes of dieback of Douglas-fir in the interior of B.C." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29780.

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Frost damage to sapling size plantation Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco.] in the central interior of B.C. was identified as the major cause of dieback and canker through tree dissections. Prominent frost rings in the wood and frost damage to buds and shoots corresponded to the dates of dieback initiation and canker events throughout the history of the plantations. Frost rings and frost cankers were reproducible using an artificial freezing technique. Symptomatic frost-damaged buds and elongating shoots were described for Douglas-fir, white spruce [Picea glauca (Moench) Voss] and subalpine fir [Abies lasiocarpa (Hook.) Nutt.]. The effect of growing season frost was most noticeable on early flushing trees. Frost and dieback damage was most severe on concave and flat landforms, which are conducive to cold air pooling on nights with strong radiative cooling. Several pathogens isolated from recently killed stems were identified from fruiting bodies and culture. Leucocytospora kunzei (Sacc.) Urban was the pathogen most commonly isolated from the edge of expanding cankers and progressive dieback margins. Sclerophoma semenospora Funk was commonly found fruiting on dead stems and leaders killed by frost or by mechanical means. Cinara pseudotaxifoliae Wilson feeding caused latent cankers on one year old leaders of Douglas-fir, which are thought to be activated by frost. Boron levels of both healthy and severely affected trees were in the intermediate range, and were not considered to play an important role in frost or pathogen susceptibility for Douglas-fir in the interior.
Forestry, Faculty of
Graduate

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Khattab, Islam Maged Abdelazeem [Verfasser], and P. [Akademischer Betreuer] Nick. "Ancestral Grapes with Resistance against Dieback: Molecular and Functional Analysis of Plant-pathogen Crosstalk in the Context of Botryosphaeriaceae Related Dieback / Islam Maged Abdelazeem Khattab ; Betreuer: P. Nick." Karlsruhe : KIT-Bibliothek, 2021. http://d-nb.info/1231361654/34.

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Mwitwa, Jacob Pacific. "Growth and physiological parameters related to shoot dieback in Pterocarpus angolensis DC seedlings." Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/20431.

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Thesis (PhD)--Stellenbosch University, 2004.
ENGLISH ABSTRACT:Six experiments, five in the glasshouse and one in the field near Nelspruit, were carried out to ascertain the effect of factors related to shoot die-back, and of water treatments on the growth and physiological responses of Pterocarpus angolensis seedlings. The study was undertaken to broaden the knowledge and understanding of the phenomenon of shoot die-back in order to enhance our ability to regenerate the species. The following experiments were carried out (a) Assessment of biomass accumulation; anatomical characteristics of the shoot apical meristem; foliar, stem and root concentration of micro- and macronutrients associated with each phenophase, (b) Effect of seedling age and seed source on the occurrence of shoot die-back under field conditions; (c) Water treatment effects on ChI. afluorescence traits of£'. angolensis seedlings obtained by assessing the fluorescence yield of photosynthetic samples subjected to dark- and light-adaptation; (d) Genetic variation in shoot die-back and other traits of sixteen halfsib families of £.. angolensis from Malawi, Namibia and Zambia grown over two die-back seasons. Experiments conducted revealed the following 1. Patterns of growth observed in phenophases are indicators of seasonal changes in annual biomass allocation to the shoot and root. Phenophases such as leaf loss and stem senescence, whether shoot die-back occurs completely or not, are directly related to the decline in above-ground biomass and declined rate of increase in root biomass respectively. Leaf flush, expansion and maturation result in increased biomass accumulation whilst shoot die-back has a minimal downregulatory effect on root biomass accumulation compared to the shoot. Shoot dieback is not sudden, therefore from the first day of germination, seedlings synchronise growth and development with the occurrence of shoot die-back. 2. Phenophasic concentration of foliar N, Ca and Mg, stem Fe and Cu and root concentrations of P, K, Mg, Fe and B are associated with shoot die-back. Patterns of mineral nutrient concentration obtained in foliage and roots but to a lesser extent in the stem, may be related to nutrient remobilisation during shoot dieback. Higher relative mineral nutrient changes during leaf yellowing and shoot die-back may be an indication of the removal of significant volumes of mobile nutrients from senescing tissues. 3. The volume of the shoot apex of E. angolensis remains constant during different phenophases which points to seasonal uniformity in the size of the apical dome. Changes in phenology associated with declined growth, or shoot die-back, is revealed through declined cell number in the tunica which is a reflection of declined mitotic activity. 4. Shoot die-back occurs in all seedlings from nursery stock planted under field conditions and all seedlings of up to two years experience complete shoot dieback. Shoot die-back takes place irrespective of seed source or the age of nursery stock that is planted. Survival after the first shoot die-back is normally low. Water treatments had no significant effect on the function of PSIJ reaction centres of P. angolensis nursery seedlings. In the case of both dark- and light-adapted leaves, water treatment had no significant effect on the measured Chi. a fluorescence parameters or the calculated parameters (specific activities, phenomenological fluxes, structure-function and performance indexes and drivingforces). 5. Water treatments affect the shape of ChI. a fluorescence transients of lightadapted compared to that of dark-adapted photosynthetic samples of E. angolensis. No significant water treatment effect was obtained for extracted and technical Chi. afluorescence parameters, specific fluxes, quantum efficiencies and phenomenological fluxes. Quantum yield, relative electron transport and quantum yield limitation, de-excitation rate constants, structure-function, performance indexes and driving forces were also not significantly different across water treatments.6. Genetic variation was observed to exist among 16 halfsib families from Malawi, Namibia and Zambia. High heritabilities were obtained for shoot die-back and other traits, indicating that shoot die-back is genetically controlled. The trait is passed from parents to offspring and it is highly probable that it occurs, throughout its natural range, in all seedlings. Since shoot die-back is genetically programmed, it remains crucial to the ability of a seedling to regenerate in the following rainy season
AFRIKAANSE OPSOMMING:Ses eksperimente, vyf in die glashuis en een in die veld naby Nelspruit, is uitgevoer om die effek van faktore wat verwant is aan die terugsterwing van lote op saailinge, sowel as om die effek van waterstres op die groei en fisiologiese responsies van Pterocarpus angolensis saailinge, te ondersoek. Die studie is ondemeem om die kennis en begrip aangaande die regenerasie-dinamika van die spesies te verbeter. Die volgende eksperimente is uitgevoer: (a) Evaluering van die effek van jisiologiese veranderings op biomassa; blaar-, stam- en wortelkonsentrasies van spoor- en makro-voedingselemente, en anatomiese eienskappe van die apikale meristeem van die lote. (b) Effek van saailingouderdom en saadbron op die voorkoms van lootterugsterwing onder veldtoestande. (c) Waterbehandelingseffekte op Chi. ajluorisensie eienskappe van ,e. angolensis saailinge wat verkry is deur die jluorisensie te evalueer van fotosintesemonsters wat aan donker- en lig-adaptasies onderwerp is. (d) Genetiese variasie in loot-terugsterwing en ander groei-eienskappe van 16 halfsib families van ,e. angolensis vanaf Malawi, Namibia en Zambia wat gekweek is oor twee terugsterj-seisoene. Die eksperimente het die volgende aan die lig gebring: 1. Groeipatrone waargeneem gedurende die fenofases is indikatore van seisoenale veranderings in jaarlikse biomassa allokasies aan die loot en die wortels. Fenofases soos blaarverlies en lootafsterwing, ongeag of loot-terugsterwing volledig is of nie, is direk verwant aan die afname in bogrondse biomassa en afnemende tempo van toename in wortelbiomassa respektiewelik. Bottende blare, vergroting en rypwording van blare lei tot toenemende biomassa akkumulasie terwyl loot-terugsterwing 'n minimale afskalende effek op akkumulasie van wortelbiomassa het in vergelyking met die van die loot. Loot-terugsterwing is nie skielik, met ander woorde vanaf die eerste dag van ontkieming sinchroniseer saailinge groei en ontwikkeling met die voorkoms van loot-terugsterwing. 2. Fenofase konsentrasies van en veranderings in blaar N en Ca en loot Fe, asook veranderings in waargenome wortel N, K, Ca, Mn, Cu, Zn en B is sterk geassosieer met loot-terugsterwing. Patrone van minerale voedingselementkonsentrasies wat in blare en wortels, en in minder mate in die loot, verkry is, mag direk verwant wees aan hermobilisering van voedingselemente gedurende loot-terugsterwing. Hoe relatiewe minerale voedingselementveranderings gedurende die vergeling van blare en lootterugsterwing mag 'n indikasie wees van die verwydering van betekenisvoUe hoeveelhede mobiele nutriente vanaf sterwende weefsel. 3. Die volume van die groeipunt van r. angolensis bly konstant gedurende verskillende fenofases wat dui op seisoenale uniformiteit in die grootte van die apikale koepel. Veranderings in fenologie ge-assosieer met afnemende groei, of loot-terugsterwing, word gerejlekteer deur afnemende selgetaUe in die tunika wat dui op afnemende mitotiese aktiwiteit. 4. VoUedige loot-terugsterwing kom voor in aUe saailinge vanaf die kwekery wat in die veld geplant word tot op die ouderdom van twee iaar. Dit kom voor angeag van saadbron of ouderdom van saailinge ten tye van planting. Oorlewing na aanvanklike loot-terugsterwing is normaalweg laag. 5. Water behandelings het geen beduidende effek op die funksie van PSII reaksiesentra van r. angolensis kewekery-saailinge gehad. Vir beide donker- en lig-aangepaste blare is geen beduidende waterbehandelingseffek verkry vir waargenome ChI. a jluoresensie parameters of die berekende parameters (spes ifieke aktiwiteite, jenomenologiese jlukse, struktuur-funksie-indekse, "perjormance-indekse oj" driving forces" ). 6. Genetiese variasie tussen 16 halfsibfamilies vanaf Malawi, Namibie en Zambie is verkry vir loot-terugsterwing en ander groei-eienskappe. Dit dui op genetiese beheer van terugsterwing en dat die eienskap oorerjbaar is, en waarskynlik in die hele natuurlike verspreidingsgebied van die spesies in aUe saailinge voorkom. Aangesien loot-terugsterwing gene ties geprogrammeer is, is dit noodsaaklik vir die vermoe van die plant om in die volgende reenseisoen te regenereer.

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12

Evans, Paul M. "Dynamics of forest ecosystem properties and resilience in a temperate woodland undergoing dieback." Thesis, Bournemouth University, 2018. http://eprints.bournemouth.ac.uk/30829/.

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Given that woodland disturbance events are expected to become more frequent and severe in the future, it is crucial to understand how fundamental underlying ecosystem properties (EPs) including biodiversity, ecosystem functions and ecosystem services will be impacted. Currently, this knowledge is severely limited, but is essential for future management of forests at both stand and landscape scales. The impact of such disturbances on EPs can be quantified through the use of ecological resilience and its associated concepts. Resilience relates to either the amount of disturbance an ecosystem can endure and still exist or the degree to which an ecosystem can resist or recover from disturbance. Resilience concepts of ecological thresholds, points of abrupt change in an EP, and resistance, persistence and recovery time are useful metrics to determine disturbance impacts. Moreover, using knowledge of how EPs are affected by disturbance, resilience assessments can enable inference of the current level of resilience that woodland has. The objectives of this thesis were therefore: 1) to determine how biodiversity, ecosystem functions and condition were affected in a forest undergoing dieback; 2) to examine the effectiveness of rapid condition assessment tools as a proxy use for inferring woodland resilience; and 3) to determine whether woodland cover influences resilience of EPs at a landscape scale. The changing condition and extent of the New Forest provided an opportunity to measure EPs across a gradient of changing condition. This was carried out through gradient analysis of dieback, based on basal area decline, at the stand scale. Using the results obtained from the gradient analysis: i) the resilience of important woodland EPs was assessed at the landscape scale using simulations of different intensities of disturbance and woodland cover, which was used as a proxy for connectivity; and ii) commonly-used forest condition assessment tools, specifically airborne lidar and the woodland Common Standards Monitoring condition assessments, were tested to determine how effective they were and whether they could be used to infer resilience at the stand scale. Overall, evidence provided in this thesis suggests that: biodiversity and functional thresholds exist as the forest degrades; current condition assessment tools are not very effective at detecting variation in woodland condition and therefore are not sufficient to infer current resilience; and woodland cover influences the resilience of important woodland EPs, at the landscape scale. All the findings are discussed in context of the New Forest, an ecologically and socio-economically important landscape.

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13

Bunny, F. "The biology, ecology and taxonomy of Phytophthora citricola in native plant communities in Western Australia /." Access via Murdoch University Digital Theses Project, 1996. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20061122.122739.

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14

Busch, Sarah Ann. "Cellular and molecular strategies to overcome macrophage-mediated axonal dieback after spinal cord injury." Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1252273911.

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15

Bunny, Felicity J. "The biology, ecology and taxonomy of Phytophthora citricola in native plant communities in Western Australia." Thesis, Bunny, Felicity J. (1996) The biology, ecology and taxonomy of Phytophthora citricola in native plant communities in Western Australia. PhD thesis, Murdoch University, 1996. https://researchrepository.murdoch.edu.au/id/eprint/492/.

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The objectives of the project were to develop an understanding of the disease dynamics caused by Phytophthora citricola in native plant communities in the south of Western Australia. Prior to 1983, the pathogen had only been reported twice from Australian forests. Since then, P. citricola has been extensively recorded from plant communities north and south of Perth, and is currently the second most frequently recovered Phytophthora species from the northern jarrah forest and the northern sandplains. The objectives were addressed by examining the biology, ecology and taxonomy of isolates of P. citricola local to the southwest. Examination of the intraspecific variation of P. citricola by isozyme analysis resolved three major electrophoretic subgroups (SG), and these were aligned with morphological and cultural variation within the species. One electrophoretic SG was confined to forested areas. This SG differed from other SGs in sporangial dimensions, growth rate on two media and in vitro sensitivity to phosphonate. A redescription of the species may be warranted. P. citricola was positively associated with two roads in the northern jarrah forest. Road surfaces were sampled, then soil overburden was removed and the surface of the concreted lateritic layer beneath was sampled. Isolation of P. citricola declined away from the road into the adjacent forest and was more frequently recovered from the caprock (up to 1 metre below soil surface) than from the soil surface. The most probable source of introduction was from infested soil on vehicles using the roads. Oospores were shown to be produced in two soils, a lateritic gravelly loam and sand, and in plants. In soil, the electrophoretic SG confined to the forest (loamy soil) produced only limited numbers of oospores in the sandy soil of the northern sandplain. The restriction of this SG to the forested areas is probably physiological, rather than limited dispersal, with the SG currently occupying the full extent of its range. Estimation of the relative persistence of oospores, zoospores and plant material colonised by P. citricola established that only oospores (either free in soil or in colonised plant material) were important in long tern survival in soil. Oospores were still viable after six months at two field sites, and after 18 months in soil in the laboratory. Phosphonate is currently the most promising method of control of Phytophthora induced disease in native plant cornmunites of the southwest. The efficacy of phosphonate against P. citricola was examined in vivo and in vitro against two SGs. Phosphonate successfully inhibited lesion growth of both SGs in vivo, but of only one electrophoretic subgroup in vitro. The ecological implications of infestation of native plant communities in the southwest of Australia are discussed.

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16

Bunny, Felicity J. "The biology, ecology and taxonomy of Phytophthora citricola in native plant communities in Western Australia." Murdoch University, 1996. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20061122.122739.

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Abstract:

The objectives of the project were to develop an understanding of the disease dynamics caused by Phytophthora citricola in native plant communities in the south of Western Australia. Prior to 1983, the pathogen had only been reported twice from Australian forests. Since then, P. citricola has been extensively recorded from plant communities north and south of Perth, and is currently the second most frequently recovered Phytophthora species from the northern jarrah forest and the northern sandplains. The objectives were addressed by examining the biology, ecology and taxonomy of isolates of P. citricola local to the southwest. Examination of the intraspecific variation of P. citricola by isozyme analysis resolved three major electrophoretic subgroups (SG), and these were aligned with morphological and cultural variation within the species. One electrophoretic SG was confined to forested areas. This SG differed from other SGs in sporangial dimensions, growth rate on two media and in vitro sensitivity to phosphonate. A redescription of the species may be warranted. P. citricola was positively associated with two roads in the northern jarrah forest. Road surfaces were sampled, then soil overburden was removed and the surface of the concreted lateritic layer beneath was sampled. Isolation of P. citricola declined away from the road into the adjacent forest and was more frequently recovered from the caprock (up to 1 metre below soil surface) than from the soil surface. The most probable source of introduction was from infested soil on vehicles using the roads. Oospores were shown to be produced in two soils, a lateritic gravelly loam and sand, and in plants. In soil, the electrophoretic SG confined to the forest (loamy soil) produced only limited numbers of oospores in the sandy soil of the northern sandplain. The restriction of this SG to the forested areas is probably physiological, rather than limited dispersal, with the SG currently occupying the full extent of its range. Estimation of the relative persistence of oospores, zoospores and plant material colonised by P. citricola established that only oospores (either free in soil or in colonised plant material) were important in long tern survival in soil. Oospores were still viable after six months at two field sites, and after 18 months in soil in the laboratory. Phosphonate is currently the most promising method of control of Phytophthora induced disease in native plant cornmunites of the southwest. The efficacy of phosphonate against P. citricola was examined in vivo and in vitro against two SGs. Phosphonate successfully inhibited lesion growth of both SGs in vivo, but of only one electrophoretic subgroup in vitro. The ecological implications of infestation of native plant communities in the southwest of Australia are discussed.

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17

Nejad, Pajand. "Pathogenic and ice-nucleation active (INA) bacteria causing dieback of willows in short rotation forestry /." Uppsala : Dept. of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, 2005. http://epsilon.slu.se/200524.pdf.

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18

Newby, Zoe Joy. "Quantification of the risk of Phytophthora dieback in The Greater Blue Mountains World Heritage area." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/10286.

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Biological invasions exert great pressure on natural ecosystems and conservation areas, the latter of which have been established to conserve biodiversity. The presence of invasive species in natural ecosystems disrupts evolutionary processes, alters species abundance and can potentially lead to extinction (Mack et al., 2000; Crowl et al., 2008). When an invasive species is the cause of plant disease, the potential for that pathogen to survive in a new environment and the expectation of the impacts it may cause, can be estimated from locations where it already occurs. Understanding the dynamics of disease is important for management and research alike, and will hopefully make way for a proactive rather than reactive response. Disease in natural Australian ecosystems caused by the invasive species Phytophthora cinnamomi has been recognised for nearly 100 years (Newhook and Podger, 1972); its devastating impacts have lead to the disease syndrome, Phytophthora dieback, being classified as a Key Threatening Process by the Australian Federal Government (Commonwealth of Australia, 2005). Yet, the assessment of potential disease establishment, that is, disease risk, is limited. This remains true for the globally significant Greater Blue Mountains World Heritage Area (GBMWHA) in New South Wales, a centre of plant and animal conservation. Not only is the understanding of the pathogen distribution limited, so too is knowledge of the potential impacts on flora and the influence climate change may have on disease expression. Management of Phytophthora dieback in the GBMWHA is made increasingly complex by the rugged and remote nature of much of the World Heritage Area, as well as competing demands from tourism, recreation and the impacts of fire and other introduced species. This study aims to address some of these complexities by establishing the suitability of the GBMWHA to P. cinnamomi, its current distribution and the potential for disease. Additionally, with the difficulty of accessing much of the GBMWHA and the risk of disease transmission in mind, an alternate approach to disease identification is trialed. The first task of this project, was concerned with understanding the potential distribution of P. cinnamomi within the GBMWHA using mechanistic modelling and information on the pathogen’s ecology. Most of the GBMHWA was found to be suitable, leading to the acceptance of the first hypothesis that the climatic and topographic conditions of the GBMWHA are conducive to P. cinnamomi establishment. The most conducive areas were characterised by high soil wetness, high rainfall and moderate temperatures, while the areas least conducive were conversely hotter and drier. Although iv the model appeared to overpredict into areas the pathogen was not found, increasing distribution risk was associated with increasing isolations, possibly indicating that the pathogen is yet to reach its potential niche. The modelled distribution of P. cinnamomi was then used to inform a field investigation to determine the actual distribution in the GBMWHA and assess the impact of the pathogen on vegetation communities and individuals. As an invasive species, the distribution of P. cinnamomi was hypothesised to be primarily found in locations with high anthropogenic activity; however it was isolated extensively from remote areas, leading to the rejection of this hypothesis. Disease was never the less expected, albeit sporadic, as per disease expression in other vegetation communities in New South Wales (Arentz, 1974; Walsh et al., 2006; Howard, 2008). Heathland communities that often have a higher incidence of disease (McDougall and Summerell, 2003), had a high rate of pathogen isolation, as well as clear indications of disease in the GBMWHA. Additionally, freshwater wetlands, many of which are endangered ecological communities under Commonwealth and State legislation, had a high rate of pathogen isolation also. The results collected during the field work were then utilised to assess the risk of Phytophthora dieback occurring in the GBMWHA within the context of the disease triangle. The distribution of P. cinnamomi was combined with models of over 130 individual host species to produce a spatially explicit model, quantifying the risk of disease. That a large portion of the GBMWHA is at risk of Phytophthora dieback was not the case, and as such this hypothesis was rejected. Although much of the World Heritage Area had a least some level of risk, greatest risk was associated with a few small areas that occurred at higher elevations with suitable rainfall and temperature conditions. Unfortunately, many of these locations were associated with high levels of tourism and recreation, highlighting the potential for anthropogenic dispersal of P. cinnamomi into, around and out of the GBMWHA. Disease itself has a temporal element which cannot be quantified in one set of field results and as disease spreads the results become outdated quickly (O'Gara et al., 2005). Field-based assessments of disease are expensive and time consuming, and in area as vast and rugged as the GBMWHA, difficult and potentially dangerous. Real-time information on the impacts of disease are therefore needed by land managers to efficiently deploy management strategies (O'Gara et al., 2005). Remote sensing offers an alternative means of assessment not requiring site entry. Vegetation condition can be assessed remotely in all manner of plant systems including the detection and quantification of disease. As such, it was hypothesised here that infection caused by P. cinnamomi could be detected from

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19

Carter, Judith. "Vegetation attributes that influence the mardo (Antechinus flavipes leucogaster) in healthy, dieback affected and rehabilitated forest." Thesis, Carter, Judith (2003) Vegetation attributes that influence the mardo (Antechinus flavipes leucogaster) in healthy, dieback affected and rehabilitated forest. Honours thesis, Murdoch University, 2003. https://researchrepository.murdoch.edu.au/id/eprint/32627/.

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20

Seebacher, Tanya Marie. "Western redcedar dieback : possible links to climate change and implications for forest management on Vancouver Island, B.C." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/32352.

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This thesis studied the distribution and potential causes of western redcedar (Thuja plicata Donn ex D. Don) dieback on the east coast of Vancouver Island, B.C. using dendrochronology and water balance modelling. Redcedar trees were cored in four of the driest and warmest biogeoclimatic (BEC) units on the island. Dieback was found in varying intensity in three of the four driest BEC units; however, it was primarily concentrated near the Qualicum Beach area (CDFmm). Ring-widths were found to be sensitive to climate on certain sites, but more complacent on other sites. Warm and dry summer climate was found to reduce radial growth of redcedar, and thus moisture stress may be the major determinant of redcedar dieback. Subsequent causes include well drained coarse textured soil conditions (predisposing), drought periods over the growing season (inciting), and contributing factors such as insects and pathogens. Water balance modelling found relationships between transpiration deficit index (TDI) and residual ring-width indices at three of the 16 study sites. The low number of significant relationships was likely caused by the low climate-sensitivity of breast-height tree ring data in redcedar growing on zonal sites. Low climate sensitivity may have been exacerbated by stand dynamics and competition, since study sites were often in mixed stands with multiple age cohorts. ForWaDy, when linked to FORECAST, could provide useful information on water stress and future growth of redcedar on the coast if linked with more climatically sensitive tree ring data. Over the next few hundred years, it is unlikely that redcedar will be lost completely from Vancouver Island due to the resilient and acclimative nature of this species; however, redcedar growing on low elevation sites vulnerable to moisture stress may experience increased dieback occurrences and eventual decline in these areas. Recommendations for future studies of redcedar dieback and considerations for forest management are provided.
Forestry, Faculty of
Graduate

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21

Cambours, Marie-Anne. "Frost-related dieback of Swedish and Estonian Salix plantations due to pathogenic and ice nucleation-active bacteria /." Uppsala : Plant Pathology and Biocontrol Unit, Swedish University of Agricultural Sciences, 2004. http://epsilon.slu.se/9600090.pdf.

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22

Adu-Acheampong, Richard Kwame. "Pathogen diversity and host resistance in dieback disease of cocoa caused by Fusarium decemcellulare and Lasiodiplodia theobromae." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/4670.

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Dieback disease caused by Fusarium and Lasiodiplodia species is a major threat to cocoa production in Ghana and elsewhere in West Africa. Current recommendations involve insecticide application to control mirid bugs whose feeding punctures provide entry points for these fungi. Little is known about the true identity of the causal pathogens of this disease. Earlier work implicated F. decemcellulare as the causal agent and more rarely L. theobromae (Cotterell, 1927; Crowdy, 1947). A total of 117 single spore fungal cultures was established from diseased cocoa stems imported from Ghana. On morphological grounds cultures could be designated as either Fusarium or Lasiodiplodia spp. The Fusarium cultures exhibited inter-isolate variability with respect to macroscopic appearance and macro-conidium morphology, suggesting the presence of more than a single species. The isolates were further characterised by PCR amplification and sequencing of the ITS region of rDNA and comparison with authentic reference cultures. Thirty-seven Fusarium isolates were identified to twenty F. chlamydosporum, nine F. solani and four isolates each of F. oxysporum and F. proliferatum. The thirty-six Lasiodiplodia isolates were identified to two species, twenty-seven L. pseudotheobromae and nine L. theobromae. In pathogenicity tests, F.chlamydosporum, F. oxysporum, F. proliferatum, F. solani and L. pseudotheobromae, previously unknown as pathogens of either cocoa or any member of the Malvaceae, caused significant wilting and dieback in Amelonado seedlings similar to that observed in the field. All isolates exhibited optimal growth at 30 °C on PDA. Disease incidence in 29 and 15 cocoa germplasm lines in the laboratory and greenhouse, respectively, showed reproducible differences in their reaction to necrotic lesion and dieback infection. LCTEEN 37/F was one of the most susceptible genotypes. CATIE1000, T85/799 and MXC 67 were the most tolerant and could be used in cocoa breeding programmes for resistance to dieback.

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Schmull, Michaela. "Site factors determining epiphytic lichen distribution in a dieback affected spruce fir forest on Whiteface Mountain, New York." Doctoral thesis, [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=965267318.

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24

Brèteau-Amores, Sandrine. "Economic analysis of adaptation options toward drought-induced risk of forest dieback : financial balance and/or carbon balance." Thesis, Université de Lorraine, 2020. http://www.theses.fr/2020LORR0158.

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Les forêts sont des écosystèmes qui jouent un rôle important dans l'adaptation de la société au changement climatique. Elles fournissent des services écosystémiques qui contribuent au bien-être humain et réduisent la vulnérabilité sociale. Or, le rythme du changement climatique s’accélère, en provoquant l'augmentation de la fréquence, de la durée et de l'intensité des événements naturels, notamment des épisodes de sécheresse extrême. En France, les épisodes de sécheresse extrême de 1976, 2003 et 2018 ont causé d’importants dommages à la forêt, à la fois immédiatement mais aussi durant plusieurs années. Les propriétaires privés peuvent protéger leurs forêts grâce à de multiples stratégies d'adaptation. Différentes stratégies d'adaptation basées sur la gestion forestière sont recommandées afin d'améliorer l'efficacité de la consommation d'eau du peuplement forestier et donc sa résistance au risque sécheresse. Le partage des risques peut être une autre option via l'assurance pour la couverture des pertes économiques. Quatre types de stratégies d'adaptation ont été testés et comparés d’un point de vue économique dans cette thèse : l'adaptation incrémentale (réduction de la durée de la révolution et réduction de la densité du peuplement), l'adaptation transitoire (diversification de la composition et de la structure) et l'adaptation transformante (substitution d'espèces) basées sur la gestion forestière, ainsi que de l'adaptation basée sur les mécanismes de marché (assurance indicielle). Pour cela, les données de sortie de modèles de croissance forestière ont servi de données d’entrée à l'approche économique. Un modèle d’assurance indicielle a aussi été développé et simulé. Pour les études de cas considérées et sous certaines hypothèses, cette thèse a donc fourni les principaux résultats suivants. Premièrement, les résultats ont prouvé que l'adaptation est pertinente pour faire face au risque de dépérissement des forêts induit par la sécheresse, qu'elle soit basée sur la gestion forestière ou sur les mécanismes de marché. Deuxièmement, la combinaison de stratégies d'adaptation basées sur la gestion forestière s’est révélée être un moyen pertinent pour adapter les forêts. La combinaison de différentes stratégies peut donc être plus bénéfique pour le propriétaire forestier que d’établir chaque stratégie séparément. Cependant, toutes les options d'adaptation ne semblent pas pertinentes, correspondant à une mauvaise adaptation. Dans le même ordre d'idées, si l'assurance forestière contre le risque de dépérissement induit par la sécheresse reste une option, le faible gain des contrats actuels peut ne pas apparaître suffisant pour inciter les propriétaires forestiers à adopter ces dits contrats
Forests are ecosystems that play an important role in the adaptation of the society to climate change. They provide ecosystem services that contribute to human well-being and reduce social vulnerability. Presently, the pace of climate change is accelerating too fast for the natural and spontaneous forest adaptation process to offset many negative impacts of climate-induced changes, such as increased frequency, duration, and intensity of mean and extreme natural events like severe drought events. In France, the extreme drought events of 1976, 2003 and 2018 caused great damage to the forest, both immediately and long after the drought episodes. Private owners can protect their forests through adaptation strategies. Different management-based adaptation strategies are recommended in order to improve the water consumption efficiency of the forest stand and thus its resistance to drought risk. Market-based strategies may be another option. Four types of adaptation strategies were tested and compared, from an economic perspective, in this thesis. These are: incremental (reduction of rotation length and reduction of stand density), transitional (composition diversification and structure diversification) and transformational (species substitution) management-based adaptation as well as a market-based adaptation (index-based insurance). For that purpose, outputs from forest growth models were used as inputs for forest economics analysis, and an index-based insurance model was developed and simulated. The main results of this thesis, for the considered case studies and under some assumptions, can be summarized as follows. First, the results proved that adaptation is a relevant strategy to mitigate drought-induced risk of dieback by the implementation of either management-based adaptation or market-based adaptation. Second, combining different management-based adaptation strategies appeared as a relevant way to adapt forests in a context of an increasing drought-induced risk of forest dieback. Indeed, the combination of different strategies was found to be more beneficial for the forest owner than each strategy implemented separately. However, not all adaptation options appeared effective, i.e., maladaptation. Finally, while forest insurance contracts covering drought-induced risk of forest dieback could be a relevant market-based option, small gains associated with current contracts are likely to prevent forest owners from adopting such insurance products

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25

Sollars, Elizabeth. "The genome and epigenome of the European ash tree (Fraxinus excelsior)." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/25977.

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European ash trees (Fraxinus excelsior ) are under threat from the fungal pathogen Hy- menoscyphus fraxineus causing ash dieback disease (ADB). Previous research has shown heritable variation in ADB susceptibility in natural ash populations. Prior to this project, very little genetic data were available for ash, thus hampering efforts to identify markers associated with susceptibility. In this thesis, I have presented nuclear and organellar assemblies of the 880 Mbp F. excelsior genome, with a combined N50 scaffold size of over 100 kbp. Using Ks distributions for six plant species, I found evidence for two whole genome duplication (WGD) events in the history of the ash lineage, one potentially shared with olive (Ks 0.4), and one potentially with other members of the Lamiales order (Ks 0.7). Using a further 38 genome sequences from trees originating throughout Europe, I found little evidence of any population structure throughout the European range of F.excelsior, but nd a substantial decrease in effective population size, both in the distant (from 10 mya) and recent past. Linkage disequilibrium is low at small distances between loci, with an r2 of 0.15 at a few hundred bp, but decays slowly from this point. From whole genome DNA methylation data of twenty F. excelsior and F. mandshurica trees, I identi ed 665 Differ- entially Methylated Regions (DMRs) between those with high and low ADB susceptibility. Of genes putatively duplicated in historical WGD events, an average of 25.9% were differen- tially methylated in at least one cytosine context, possibly indicative of unequal silencing. Finally, I found some variability in methylation patterns among clonal replicates (Pearson's correlation coefficient 0.960), but this was less than the variability found between different genotypes ( 0.955). The results from this project and the genome sequence especially, will be valuable to researchers aiming to breed or select ash trees with low susceptibility to ADB.

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26

Jordan, Stephen Andrew. "Epidemiology and etiology of Eutypa dieback of grapevine and partial characterization of Eutypella vitis, a new pathogen of grapevine." Diss., Connect to online resource - MSU authorized users, 2008.

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27

Pilbeam, Ros. "Effects of phosphite on disease development and histological responses in Eucalyptus marginata infected with Phytophthora cinnamomi." Thesis, Pilbeam, Ros (2003) Effects of phosphite on disease development and histological responses in Eucalyptus marginata infected with Phytophthora cinnamomi. PhD thesis, Murdoch University, 2003. https://researchrepository.murdoch.edu.au/id/eprint/260/.

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Abstract:

Phosphite is currently used for the management of Phytophthora cinnamomi in native plant communities. A greater understanding of how phosphite affects the host-pathogen interaction is required in order to determine the most effective treatment. This thesis aimed to investigate the effects of applied phosphite concentration on phytotoxicity, in planta concentration of phosphite, disease development and anatomical responses of Eucalyptus marginata. Spraying the foliage to run-off with 7.5 and 10 g phosphite/L led to the development of severe leaf necrosis within 7 days, with greater than 60% of the leaf area damaged. Moderate phytotoxicity was observed after treatment with 5 g phosphite/L. In planta concentration of phosphite in stems, lignotubers and roots did not differ significantly between applied concentrations of phosphite. Stem tissue contained the largest concentration of phosphite at one week after spraying, with approximately 210 and 420 g phosphite/g dry weight detected after treatment with 5 and 10 g phosphite/L, respectively. In a subsequent field trial, the applied concentration of phosphite was found to affect the duration of effectiveness of phosphite in protecting E. marginata seedlings from stem colonisation by P. cinnamomi. Plants were wound-inoculated with P. cinnamomi at 6-monthly intervals after spraying with phosphite. The 2.5 and 5 g phosphite/L treatments were effective against colonisation by P. cinnamomi when inoculated 0 and 6 months after spraying, but only the 5 g phosphite/L treatment inhibited P. cinnamomi within 12 months of spraying. Phosphite had no effect on colonisation by P. cinnamomi when plants were inoculated at 17 months after spraying. The in planta concentration of phosphite detected in the leaves, stems and roots of plants treated with 5 g phosphite/L did not differ significantly between the time of harvest or tissue type at 0.2 and 6 months after spraying. P. cinnamomi remained viable in plants treated with phosphite.Treatment with 2.5 and 5 g phosphite/L when P. cinnamomi was well established in the stems was ineffective at preventing the death of E. marginata. Between 45 and 89% of plants were girdled on the day of spraying. Spraying plants with 2.5 and 5 g phosphite/L when conditions were less favourable for the pathogen reduced the mortality of E. marginata for up to 10 months. E. marginata seedlings responded to damage by P. cinnamomi with the production of kino veins and woundwood. Bark lesions were in the process of being sloughed off by 7 months after inoculation in plants that remained alive. In plants of a resistant (RR) clonal line and susceptible (SS) clonal line, phosphite treatment inhibited lesion extension in stems, but lesions did not indicate the amount of stem colonised by P. cinnamomi. The pathogen was isolated from up to 17 cm beyond the lesion front in the RR clonal line. Treatments that reduced the mortality of E. marginata were 5 g phosphite/L in the RR clonal line (RR/5) and 10 g phosphite/L in the SS clonal line (SS/10). Uninoculated plants were wounded with liquid nitrogen to determine the microscopic responses to injury in the absence of the pathogen. Wound closure was achieved within 21 days of wounding, with callus formation and vascular cambium regeneration. A wound periderm separated wounded tissue from healthy tissue, adjacent to a lignified boundary zone. Two types of phellem were observed - thin-walled phellem (TnP) and thick-walled phellem (TkP). The first-formed TnP layers contained variable-shaped cells, while subsequent layers were more cubical in shape. Multiple TnP layers developed up to 42 days after wounding, with TkP cells sandwiched between the TnP layers. Genotype and phosphite treatment did not affect the wound responses. Inoculated plants with a restricted lesion extension also formed a wound periderm to separate damaged tissue from healthy tissue. Phosphite treatment stimulated the responses to P. cinnamomi in both clonal lines. Early development of the wound periderm was visible by 6 days after phosphite treatment. It waspreceded by the formation of a ligno-suberised boundary zone in the cambial zone and in phloem parenchyma cells existing prior to injury. Suberin was not detected in the SS/0 treatment. TnP layers completely surrounded lesioned tissue in plants still alive by 24 days after phosphite treatment. Extensive callus production was evident in the SS/10, RR/5 and RR/10 treatments. Temperature affected the post-inoculation efficacy of phosphite and anatomical responses of E. marginata. At 20 degrees C lesion extension was restricted in both clonal lines of E. marginata, irrespective of phosphite treatment. Greater than 70% of inoculated plants in all treatments produced a ligno-suberised boundary zone at 20 degrees C and between 30 and 70% formed a wound periderm. At 28 degrees C, lesion extension was reduced in phosphite-treated plants at 7 days after treatment. However, lesions continued to extend up to 5 mm per day in the SS clonal line and very few SS plants formed a wound periderm at the lesion front. This contrasted with the strong responses to abiotic wounding observed in uninoculated SS plants at 28 degrees C. The most extensive responses to P. cinnamomi were detected in the RR/5 treatment at 28 degrees C, with a ligno-suberised boundary zone and differentiated TnP of a wound periderm observed in greater than 70% of plants. This treatment resulted in significantly less girdled plants than all other treatments at 28 degrees C, including the RR/0 treatment. At 23 and 24 degrees C, there was no significant difference in acropetal lesion extension or circumferential lesion spread between clonal lines. The inoculation technique and environmental conditions may have resulted in too high a disease pressure for a full expression of resistance in the RR clonal line. This thesis demonstrates that phosphite has the potential to enhance the resistance of young E. marginata and enable them to survive infection by P. cinnamomi. However, its effectiveness is dependent upon a number of factors, including host resistance, environmental conditions, the applied phosphite concentration and the timing of application.

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28

Pilbeam, Ros. "Effects of phosphite on disease development and histological responses in Eucalyptus marginata infected with Phytophthora cinnamomi." Murdoch University, 2003. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040820.140206.

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Abstract:

Phosphite is currently used for the management of Phytophthora cinnamomi in native plant communities. A greater understanding of how phosphite affects the host-pathogen interaction is required in order to determine the most effective treatment. This thesis aimed to investigate the effects of applied phosphite concentration on phytotoxicity, in planta concentration of phosphite, disease development and anatomical responses of Eucalyptus marginata. Spraying the foliage to run-off with 7.5 and 10 g phosphite/L led to the development of severe leaf necrosis within 7 days, with greater than 60% of the leaf area damaged. Moderate phytotoxicity was observed after treatment with 5 g phosphite/L. In planta concentration of phosphite in stems, lignotubers and roots did not differ significantly between applied concentrations of phosphite. Stem tissue contained the largest concentration of phosphite at one week after spraying, with approximately 210 and 420 µg phosphite/g dry weight detected after treatment with 5 and 10 g phosphite/L, respectively. In a subsequent field trial, the applied concentration of phosphite was found to affect the duration of effectiveness of phosphite in protecting E. marginata seedlings from stem colonisation by P. cinnamomi. Plants were wound-inoculated with P. cinnamomi at 6-monthly intervals after spraying with phosphite. The 2.5 and 5 g phosphite/L treatments were effective against colonisation by P. cinnamomi when inoculated 0 and 6 months after spraying, but only the 5 g phosphite/L treatment inhibited P. cinnamomi within 12 months of spraying. Phosphite had no effect on colonisation by P. cinnamomi when plants were inoculated at 17 months after spraying. The in planta concentration of phosphite detected in the leaves, stems and roots of plants treated with 5 g phosphite/L did not differ significantly between the time of harvest or tissue type at 0.2 and 6 months after spraying. P. cinnamomi remained viable in plants treated with phosphite.Treatment with 2.5 and 5 g phosphite/L when P. cinnamomi was well established in the stems was ineffective at preventing the death of E. marginata. Between 45 and 89% of plants were girdled on the day of spraying. Spraying plants with 2.5 and 5 g phosphite/L when conditions were less favourable for the pathogen reduced the mortality of E. marginata for up to 10 months. E. marginata seedlings responded to damage by P. cinnamomi with the production of kino veins and woundwood. Bark lesions were in the process of being sloughed off by 7 months after inoculation in plants that remained alive. In plants of a resistant (RR) clonal line and susceptible (SS) clonal line, phosphite treatment inhibited lesion extension in stems, but lesions did not indicate the amount of stem colonised by P. cinnamomi. The pathogen was isolated from up to 17 cm beyond the lesion front in the RR clonal line. Treatments that reduced the mortality of E. marginata were 5 g phosphite/L in the RR clonal line (RR/5) and 10 g phosphite/L in the SS clonal line (SS/10). Uninoculated plants were wounded with liquid nitrogen to determine the microscopic responses to injury in the absence of the pathogen. Wound closure was achieved within 21 days of wounding, with callus formation and vascular cambium regeneration. A wound periderm separated wounded tissue from healthy tissue, adjacent to a lignified boundary zone. Two types of phellem were observed thin-walled phellem (TnP) and thick-walled phellem (TkP). The first-formed TnP layers contained variable-shaped cells, while subsequent layers were more cubical in shape. Multiple TnP layers developed up to 42 days after wounding, with TkP cells sandwiched between the TnP layers. Genotype and phosphite treatment did not affect the wound responses. Inoculated plants with a restricted lesion extension also formed a wound periderm to separate damaged tissue from healthy tissue. Phosphite treatment stimulated the responses to P. cinnamomi in both clonal lines. Early development of the wound periderm was visible by 6 days after phosphite treatment. It waspreceded by the formation of a ligno-suberised boundary zone in the cambial zone and in phloem parenchyma cells existing prior to injury. Suberin was not detected in the SS/0 treatment. TnP layers completely surrounded lesioned tissue in plants still alive by 24 days after phosphite treatment. Extensive callus production was evident in the SS/10, RR/5 and RR/10 treatments. Temperature affected the post-inoculation efficacy of phosphite and anatomical responses of E. marginata. At 20°C, lesion extension was restricted in both clonal lines of E. marginata, irrespective of phosphite treatment. Greater than 70% of inoculated plants in all treatments produced a ligno-suberised boundary zone at 20°C and between 30 and 70% formed a wound periderm. At 28°C, lesion extension was reduced in phosphite-treated plants at 7 days after treatment. However, lesions continued to extend up to 5 mm per day in the SS clonal line and very few SS plants formed a wound periderm at the lesion front. This contrasted with the strong responses to abiotic wounding observed in uninoculated SS plants at 28°C. The most extensive responses to P. cinnamomi were detected in the RR/5 treatment at 28°C, with a ligno-suberised boundary zone and differentiated TnP of a wound periderm observed in greater than 70% of plants. This treatment resulted in significantly less girdled plants than all other treatments at 28°C, including the RR/0 treatment. At 23 and 24°C, there was no significant difference in acropetal lesion extension or circumferential lesion spread between clonal lines. The inoculation technique and environmental conditions may have resulted in too high a disease pressure for a full expression of resistance in the RR clonal line. This thesis demonstrates that phosphite has the potential to enhance the resistance of young E. marginata and enable them to survive infection by P. cinnamomi. However, its effectiveness is dependent upon a number of factors, including host resistance, environmental conditions, the applied phosphite concentration and the timing of application.

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29

Kotze, Louis Jacobus Daniel. "Risk assessment of the Acacia cyclops dieback pathogen, Pseudolagarobasidium acaciicola, as a mycoherbicide in the South African strandveld and limestone fynbos." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86551.

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Thesis (MSc)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Acacia cyclops, an invasive weed in South Africa, was initially imported to stabilize the sand dunes in the southern Cape. The spread of A. cyclops is a major threat to the fragile biodiversity of the strandveld and limestone fynbos vegetation. Acacia cyclops dieback has been observed for some time, although the causative agent, Pseudolagarobasidium acaciicola, has only recently been described. This fungus is nominated for development as a mycoherbicide to control A. cyclops. Although current biological and mechanical control efforts are proving to be partially effective, A. cyclops is still causing major damage to natural ecosystems. The introduction of a mycoherbicide would increase the cost effectiveness of controlling this weed in the long term. The majority of the literature that was reviewed supports the use of mycoherbicides as biocontrol agents, especially when taking into account the decrease in acceptance and availability of chemical control agents. Considering that the Pseudolagarobasidium genus consists of saprobes, opportunistic facultative pathogens and endophytes, P. acaciicola is predicted to have similar biological characteristics. The species is also highly likely to be indigenous, although with a wider distribution range than previously envisaged. Strict precautions should still however be taken to ensure that non-target species will not be threatened. This study consists of a unique risk assessment comprising different sections. A field survey was performed to record disease incidence among indigenous woody plant species around 100 diseased A. cyclops trees. Subsequently, DNA extractions were made from the roots of the diseased indigenous plants and A. cyclops trees to verify the presence of P. acaciicola. Of the 2432 indigenous woody plants observed, 22 (0.9%) were dead or dying, while P. acaciicola was detected in 10 of these (0.4%), representing six species. Pseudolagarobasidium acaciicola was detected in 47% of the A. cyclops trees. Although P. acaciicola could be a weak pathogen in a broad range of indigenous plant species, the extremely low disease incidence is an indication of a low level of risk associated with using P. acaciicola as a mycoherbicide. Additionally, pathogenicity trials on indigenous plant species were conducted to give an indication of host susceptibility. A total of 30 indigenous plant species were wound inoculated at two field sites, and potted plants representing 17 indigenous plant species were wound and soil inoculated in a nursery. The optimum growth temperature for P. acaciicola was determined in order to understand it’s seasonal and landscape preference. Mortality was recorded in five of nine indigenous Fabaceae species, while a single plant each of four other non-Fabaceae species died after inoculation. No plants outside the Fabaceae family died in the field. Only A. cyclops seedlings died following soil inoculation. Longitudinal sections of stem inoculated plants revealed no systemic infection in Fabaceae species that survived inoculation. Infection in susceptible Fabaceae species was generally more extensive than infection in susceptible non-Fabaceae species. The optimum growth rate for P. acaciicola was determined at 35°C, indicating an adaptation to summer conditions. Indigenous Fabaceae species do display greater susceptibility than species from other families, indicating some level of specificity, although susceptible species can not be phylogenetically circumscribed. Aside from being a facultative pathogen on A. cyclops, results from this study suggest that P. acaciicola is primarily a saprophyte and an occasional opportunistic pathogen on some indigenous Fabaceae, possibly only being a weak opportunistic pathogen on some non-Fabaceae species. However, the risk of not effectively managing A. cyclops populations in these threatened vegetation types outweighs the risk associated with using P. acaciicola as a mycoherbicide. Therefore the use of P. acaciicola as a mycoherbicide on A. cyclops would be recommended, provided that sufficient monitoring of treated sites is implemented that primarily focus on the indigenous Fabaceae species. The effective control of A. cyclops could be achieved when P. acaciicola is used to compliment current mechanical, biological and chemical control methods in an integrated management strategy.
AFRIKAANSE OPSOMMING: Acacia cyclops, ook bekend as rooikrans, is ‘n indringerplant in Suid-Afrika wat oorspronklik vanaf Australië ingevoer is om die sandduine in die Kaap te stabiliseer. Die verspreiding van rooikrans bedreig die sensitiewe biodiversiteit van die strandveld en kalksteen fynbos. Rooikrans terugsterwing is al vir ‘n geruime tyd opvallend in die grootste deel van die plant se verspreiding in Suid-Afrika, alhoewel die veroorsakende organisme, Pseudolagarobasidium acaciicola, eers onlangs beskryf is. Hierdie swam is as ‘n geskikte kandidaat vir die ontwikkeling van ‘n biologiese onkruiddoder om rooikrans te beheer, genomineer. Alhoewel die huidige biologiese- en meganiese beheer metodes vir rooikrans gedeeltelik suksesvol is, hou dié indringer steeds ‘n ernstige bedreiging vir die natuurlike ekosisteme in. Die gebruik van ‘n swam-gebaseerde onkruiddoder sal die beheer van rooikrans oor die langtermyn meer koste-effektief maak. Die oorgrote meerderheid van die literatuur wat hersien is, ondersteun die gebruik van swam-gebaseerde onkruiddoders as biologiese beheermiddels, veral as die afname in aanvaarbaarheid en beskikbaarheid van chemiese beheermiddels in ag geneem word. Aangesien die Pseudolagarobasidium genus uit saprofiete, opportunistiese fakultatiewe patogene en endofiete bestaan, word daar voorspel dat P. acaciicola ‘n soortgelyke biologiese karakter sal hê. Dit is hoogs waarskynlik dat hierdie swamspesie inheems is, alhoewel die verspreiding wyer mag wees as wat oorspronklik voorspel is. Streng maatreëls moet egter steeds in plek wees om te verseker dat nie-teiken plantspesies nie bedreig word nie. Hierdie studie bestaan uit ‘n unieke risiko-analise met verkeie onderafdelings. ‘n Veld-opname is uitgevoer om die siekte-voorkoms van die inheemse houtagtige plantspesies rondom ‘n 100 siek rooikrans plante te bepaal. DNA ekstraksies is vervolgens vanuit die wortels van siek inheemse plantspesies en -rooikrans uitgevoer, om uiteindelik die teenwoordigheid van P. acaciicola binne die hout te kon bevestig. Uit ‘n totaal van 2432 inheemse houtagtige plante wat aangeteken is, was 22 (0.9%) siek of dood, terwyl die teenwoordigheid van P. acaciicola in 10 van hierdie plante (0.4%), wat ses spesies teenwoordig, bevestig is. Die teewoordigheid van P. acaciicola is ook in 47% van die rooikrans bevestig. Alhoewel P. acaciicola moontlik ‘n swak opportunistiese patogeen op ‘n verskeidenheid inheemse plantspesies is, dui die lae verhouding van dooie inheemse plante teenoor gesonde plante in die veld op ‘n lae risiko vir die gebruik van P. acaciicola as ‘n biologiese onkruiddoder. Patogenisiteitstoetse is op inheemse plantspesies uitgevoer om ‘n aanduiding van gasheervatbaarheid te verkry. Wond-inokulasies is op ‘n totaal van 30 inheemse plantspesies by twee veldstudie-areas uitgevoer, terwyl wond- en grond-inokulasies op 17 inheemse spesies potplante in die kweekhuis uitgevoer is. Die optimale temperatuur waarby P. acaciicola groei, is bepaal om die swam se seisoenale- en habitatsvoorkeure beter te verstaan. Plante van vyf uit die nege inheemse Fabaceae spesies het doodgegaan, terwyl ‘n enkele plant van vier nie-Fabaceae spesies doodgegaan het. Alle plante buite die Fabaceae familie het oorleef in die veld na inokulasie. Slegs rooikranssaailinge het na grond inokulasie doodgegaan. Lengtedeursnee van die stam en wortels van elke geïnokuleerde plant het bevestig dat daar geen sistemiese infeksie in Fabaceae spesies wat inokulasie oorleef het, plaasgevind het nie. Infeksies in vatbare Fabaceae spesies was oor die algemeen meer ernstig as infeksies in vatbare nie-Fabaceae spesies. Die optimale groei van P. acaciicola het by 35°C plaasgevind, wat aandui op ‘n voorkeur vir somerstoestande. Inheemse Fabaceae spesies het meer vatbaar as vatbare plantspesies van ander families voorgekom. Hierdie verskynsel dui op ‘n sekere vlak van spesifisiteit, alhoewel daar geen duidelike filogenetiese grense vir vatbare spesies bepaal kon word nie. Behalwe vir die feit dat P. acaciicola ‘n fakultatiewe patogeen op rooikrans is, stel resultate van hierdie studie voor dat hierdie swam hoofsaaklik ‘n saprofiet is wat soms ook ‘n opportunisties patogeen op sekere inheemse Fabaceae is en moontlik slegs ‘n swak opportunistiese patogeen op plantspesies buite die Fabaceae familie is. Die swak en oneffektiewe bestuur van rooikrans in hierdie bedreigde plantegroeitipes hou egter ‘n groter bedreiging in as die gebruik van P. acaciicola as ‘n biologiese onkruiddoder. Pseudolagarobasidium acaciicola word daarom aanbeveel vir die beheer van rooikrans, mits voldoende monitering, wat fokus op inheemse Fabaceae spesies, gepaard gaan met die gebruik van hierdie biologiese onkruiddoder. Rooikrans kan effektief beheer word as P. acaciicola ingespan word om huidige meganiese-, biologiese- en chemiese beheermetodes in ‘n geïntegreerde bestuurstrategie te komplimenteer.

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30

Hesse, Volker. "Epiphytic lichen diversity and its dependence on chemical site factors in differently elevated dieback-affected spruce stands of the Harz Mountains /." Berlin : J. Cramer, 2002. http://catalogue.bnf.fr/ark:/12148/cb41308907z.

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31

Graham, Tristian. "The impact of Phytophthora dieback and the aerial application of phosphite on terrestrial invertebrate communities of south coast heathlands, Western Australia." Thesis, Graham, Tristian (2003) The impact of Phytophthora dieback and the aerial application of phosphite on terrestrial invertebrate communities of south coast heathlands, Western Australia. Honours thesis, Murdoch University, 2003. https://researchrepository.murdoch.edu.au/id/eprint/32628/.

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Terrestrial invertebrates were surveyed from south coast heathland environments, Gull Rock and Waychinicup National Park. These study sites chosen from within these two regions consist of both healthy and Phytophthora cinnamomi infected vegetation. Phosphite was being aerially applied to parts of these sites as a preventative treatment for the further spread of Phytophthora dieback disease into healthy areas. The experiment aimed to sample terrestrial invertebrate communities using pitfall traps and a foliage beating technique in Phytophthora dieback affected areas and healthy areas and also before and after phosphite application to assess any potential non-target impacts. Invertebrates were identified and analaysed at ordinal level classification and Coleoptera (beetles) were sorted to morphospecies to assess impacts at a finer taxonomic level. Shannon-Wiener Index of Diversity, Sorenses Index of Similarity, Multi-dimesional Scaling, Multi-variate ANOVA and Univariate ANOV A were all used to decide whether there were any impacts of Phytophthora dieback and Phosphite Application of the invertebrates collected. Analysis revealed strong seasonal effects within data but no trends eluding to impact of Phytophthora dieback or Phosphite application.

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32

Harada, Yota. "Climate-driven mangrove dieback in the Gulf of Carpentaria, Australia: using stable isotopes as a tool to assess and monitor ecosystem changes." Thesis, Griffith University, 2020. http://hdl.handle.net/10072/393196.

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Extreme climatic events can trigger sudden but often long-lasting and irreversible changes in ecosystems by causing mortality of foundation (habitat-forming) species. The magnitude and frequency of such events are likely to increase due to human-induced climate change, but the dynamics of such extreme biological events remain poorly understood, with only a limited number of case studies reported in the past. In many cases, assessing the impact of rare, extreme biological events can be challenging because these events can be unexpected and sudden, often making pre-event sampling not achievable. In late 2015 to early 2016, an extensive area of mangrove forest along ~ 1,000 km of coastline in the Gulf of Carpentaria, Australia, experienced severe dieback as a result of a climatic extreme event that included extreme temperatures, drought conditions and lower than average sea levels. My research aimed to address a knowledge gap in the effects of extreme climatic events on intertidal coastal ecosystems by assessing the ecological impacts of mass mortality of mangrove trees on the intertidal ecosystem. This aim was achieved through the use of a comparative experiment of an impacted forest and an adjacent unimpacted forest using traditional ecological survey techniques combined with conventional bulk stable isotope analyses and a more novel compound-specific isotope analysis of amino acids. My research also offers significant insights into the use of the more novel compound-specific isotope analysis of amino acids to complement the conventional bulk stable isotope analysis in mangrove ecosystem trophic analyses. Firstly, I used a combination of traditional ecological survey techniques and bulk stable isotope analysis of carbon (C) and nitrogen (N) to measure the effects of mangrove forest mortality on benthic faunal communities, with a focus on functional aspects of food web dynamics. I tested if changes in benthic faunal assemblages would be evident due to mangrove mortality, and if food web structure was impacted by the mangrove mortality and alternations in available food resources. I found that in the forest that experienced tree mortality, there were fewer crabs that relied on mangrove litter as a food source but more crabs that fed on the microphytobenthos. As the microphytobenthos was largely unaffected by the die-back event, they provided a buffer to the food-web responses. The infauna, e.g. burrowing crabs, was also largely unaffected by the mortality effect. However, overall, the habitat value for mangrove ecosystem services could be decreased due to lower physical habitat complexity following tree losses. Secondly, the initial dieback and recovery of the impacted mangrove ecosystem were evaluated using a combination of bulk stable C, N and S isotopes and a more novel amino acid compound-specific isotope method. I tested if tree mortality changed the overall circulation of C, N and S elements, and if this change would be reflected in δ13C, δ15N and δ34S values of mangrove ecosystem components such as mangrove plants, soil and associated animals. I also tested if/how these isotopic compositions change over time with the recovery of mangrove vegetation. Stable isotope analyses confirmed significant changes to the circulation of C, N and S elements following tree mortality. Recovery of the mangrove vegetation was evident from increased numbers of mangrove seedlings and saplings in the impacted forest over the two-year survey, but recovery of CNS cycling was not evident even after 30 months, suggesting a long-lasting effect of the mortality event. Finally, the use of bulk stable CNS isotopes and more novel compound-specific stable C and N isotopes of amino acids were compared to evaluate which isotopic compositions are more conservative tracers of mangrove organic matter and suited for analyses of mangrove food webs. I tested if stable isotopic compositions in essential amino acids that cannot be synthesised by animals would be more conservative in food web links between consumers and mangrove organic matter. Isotopic compositions in essential amino acids effectively separated mangrove organic matter from the microphytobenthos and helped to trace mangrove organic matter in a mangrove food web. These more sophisticated tracing techniques complemented traditional bulk stable isotope analyses by providing improved resolving power in mangrove trophic analyses. The outcome of this research will be an important contribution to the emerging global body of case studies that show significant ecological impacts driven by extreme climatic events, and how changes in habitat forming species result in significant impacts on ecosystem community dynamics as well as biogeochemical processes including C, N and S cycling. My research also provides a framework for combining the use of conventional and novel stable isotope measurements with traditional ecological survey techniques in reporting difficult to measure impacts of extreme biological events. The results of this research may also be used for planning and future-proofing coastal wetlands from future impacts of climatic extreme events, and support wetland conservation and restoration efforts.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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McDougall, Keith L. "Vegetation patterns in the northern jarrah forest of Western Australia in relation to dieback history and the current distribution of Phytophthora cinnamomi." Thesis, McDougall, Keith L. (1996) Vegetation patterns in the northern jarrah forest of Western Australia in relation to dieback history and the current distribution of Phytophthora cinnamomi. PhD thesis, Murdoch University, 1996. https://researchrepository.murdoch.edu.au/id/eprint/51870/.

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Dieback, largely attributed to the fungal plant pathogen Phytophthora cimiamomi, is characterized in the northern jarrah forest by multiple deaths of many plant species, including the dominant, Eucalyptus ruarginata (jarrah), a species of great commercial importance. The wide host range of the pathogen has major implications for the biodiversity of the ecosystem. The first records of dieback in the jarrah forest were made in the 1920s. Despite the magnitude and long history of the impact in the jarrah forest, little is known about the vegetation changes that result from dieback. In this dissertation, I develop a model of vegetation change related to dieback by examining the vegetation of a range of dieback sites and relating the patterns identified to the current distribution of P. cinnamomi. The study is the first explicit investigation of floristic and structural patterns on dieback sites in the jarrah forest. Substantial floristic differences were found between dieback and unaffected vegetation. The patterns are strongly correlated with the age of the original dieback event. There was little difference, however, in the mean number of species/quadrat between dieback and unaffected vegetation. The time since the inception of dieback was estimated using aerial photography. The oldest dieback sites located had been affected prior to 1951. Of the species found less frequently on these old dieback sites, 64% had not previously been associated with P. cinnamomi infection. Some of these were assessed for their susceptibility in glasshouse pathogenicity tests. New records of susceptibility were made at the species, genus and family levels. Several species regarded as being highly susceptible to infection by P. cinnamomi were found as frequently on old dieback sites as in unaffected vegetation. Many of the species found more frequently on dieback sites were probably present at the time of the initial dieback event. Others, mostly annuals, may have been introduced from nearby vegetation types with open canopies, such as granite outcrops. If plant invasions have occurred following dieback, the small differences in species richness between dieback and unaffected vegetation may hide a great reduction in species richness due to dieback. Structural changes following dieback may have a profound effect on some species regardless of their susceptibility to infection. A spatial association with trees on dieback sites was demonstrated for a range of species. The apparent reliance of some understorey species on tree cover is discussed in relation to current theories of patch dynamics. Two methods were used to isolate P. cinnamomi from dieback sites. In situ Banksia grandis baits were more effective at detecting P. cinnamomi than ex situ baited soils, especially when P. cinnamomi was apparently rare. P. cinnamomi was frequently isolated from creek edges with a long history of dieback and from active dieback fronts but was rarely found on sloping dieback sites affected prior to 1980. It is not clear if the P. cinnamomi present on pre-1951 dieback sites has persisted there since the initial dieback event or been re-introduced from active dieback fronts upslope. Very few highly susceptible species appear to be totally eliminated by the pathogen at the time of the initial dieback event. The mass deaths at that time are followed by a period of recolonization of susceptible species with highly germinable seed. The survival of the new cohort of these species is a function of the time taken to produce another crop of seed. Susceptible species may persist on the pre-1951 dieback sites because of highly germinable seed, young reproductive age, copious seed production and animal dispersal. The rarity of P. cinnamomi on these sites must greatly contribute to their persistence. Pathogenicity testing in excised stems indicated that resistance to the movement of P. cinnamomi in plant tissue develops in jarrah populations on many dieback sites, although it is unlikely to be integral to regeneration. Evidence of resistance in other species investigated could not be found. The key elements in the model of vegetation change developed in the thesis are (i) the on-going occurrence of P. cimiamomi on dieback sites, (ii) the susceptibility of plant species to infection by P. cimiamomi, (iii) the sensitivity of plant species to structural changes, (iv) the proportion of a plant population killed, (v) the capacity of plant species for rapid recruitment after dieback, (vi) the time taken for plant species from germination to reproduction, and (vii) the capacity of plant species to invade. Stochastic factors such as fire, logging, climatic perturbations, and diseases caused by other pathogens, cannot be quantified and easily incorporated into the model. Predictions are made about the future vegetation of dieback sites, contingent on intervention by forest managers. An epidemic - recovery cycle, involving concomitant fluctuations in pathogen and host populations, has been hypothesized by some authors for sites affected by P. cimiamomi. There is evidence of such a cycle on a small scale. On a larger scale, epidemics on dieback sites in the jarrah forest may be isolated in space and time. The importance of long-term ecological studies of jarrah forest vegetation to our understanding of natural forest processes and the effects of dieback is stressed.

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Laidlaw, William Scott, and mikewood@deakin edu au. "The Effects of Phytophthora Cinnamomi on heathland flora and fauna of the Eastern Otway Ranges." Deakin University. School of Biological and Chemical Sciences, 1997. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20051111.121612.

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The plant pathogen, Phytophthora dnnamomi, is a cause of dieback disease observed in sclerophyll vegetation in Australia, The effects of P. dnnamomi on flora and fauna were studied at two locations in heathland vegetation near the coastal town of Anglesea, Victoria. The pathogen was isolated from soils beneath diseased heathland plants. The extent of diseased vegetation was assessed by the presence and absence of highly sensitive indicator species, Xanthorrhoea australis and hopogon ceratophyllus. The characteristics of heathland vegetation exhibiting dieback disease associated with the presence of P. dnnamomi were investigated. Plant species richness was similar between diseased and non-diseased areas however diseased areas were characterised by significant declines in the cover and frequency of susceptible species, increases in resistant species and increases in percent cover of open ground. Compared to non-diseased areas, diseased areas exhibited fewer shrub species and decreased shrub cover. The percentage cover and number of species of sedges, lilies and grasses were higher in diseased areas. Structural differences were significant between 0-0.6 m with decreased cover of vegetation in diseased areas. Differences in structure between diseased and non-diseased areas were not as great as expected due to increases in the cover of resistant species. A number of regenerating X australis were observed in post-disease areas. Cluster analysis of floristic data could clearly separate diseased and non-diseased trap stations. The population dynamics and habitat use of eight small mammal species present were compared in diseased and non-diseased areas using trapping and radio-tracking techniques. The number of small mammal species captured in post-disease areas was significantly lower than non-diseased areas. Mean captures of Antechinus stuartii and Rattus fiisdpes were significantly lower in diseased areas on Grid B. Mean captures of Rattus lutreolus were significantly lower in diseased areas on both study grids. Significant differences were not observed in every season over the two year study period. Radio tracking revealed more observations of Sminthopsis leucopus in non-diseased vegetation than in diseased. Cercartetus nanus was frequently observed to utilise the disease susceptible X. australis for nesting. At one location, the recovery of vegetation and small mammal communities in non-diseased and diseased vegetation after fuel reduction burning was monitored for three years post-fire. Return of plant species after fire in both disease classes were similar, reaching 75% of pre-fire richness after three years. Vegetation cover was slower to return after fire in diseased areas. Of the seven small mammal species captured pre-fire, five were regularly captured in the three years after fire. General linear model analysis revealed a significant influence of disease on capture rates for total small mammals before fire and a significant influence of fire on capture rates for total small mammals after fire. After three years, the influence of fire on capture rates was reduced no significant difference was detected between disease classes. Measurements of microclimate indicate that diseased, burnt heathland was likely to experience greater extremes of temperature and wind speed. Seeding of diseased heathland with X. australis resulted in the establishment of seedlings of this sensitive species. The reported distributions of the mamma] species in Victoria were analysed to determine which species were associated with the reported distribution of dieback disease. Twenty-two species have more than 20% of their known distribution in diseased areas. Five of these species, Pseudomys novaehollandiae, Pseudomys fumeust Pseudomys shortridgei, Potorous longipes and Petrogale pencillata are rare or endangered in Victoria. Four of the twenty-two species, Sminthopsis leucopus, Isoodon obesulus, Cercartetus nanus and Rottus lutreolus am observed in Victorian heathlands. Phytophthora cinnamomi changes both the structure and floristics of heathland vegetation in the eastern Qtway Ranges. Small mammals respond to these changes through decreased utilisation of diseased heathland. The pathogen threatens the diversity of species present and future research efforts should be directed towards limiting its spread and rehabilitating diseased areas.

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au, M. Wheeler@murdoch edu, and Margaret Wheeler. "Reproductive and Molecular Biology of Eucalyptus marginata." Murdoch University, 2004. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040723.140250.

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This thesis examined aspects of the reproductive and molecular biology of Eucalyptus marginata (jarrah). The aims were to develop protocols for controlled pollination, that could be used in clonal orchard trees to breed jarrah seedlings that have a known genetic resistance to Phytophthora cinnamomi (dieback), for use in rehabilitation after mining and logging. An intimate knowledge of the breeding biology of jarrah was necessary to achieve this aim. The project also aimed to increase knowledge of the genetic diversity and structure of jarrah, in order to make informed decisions regarding the collection of material to be used for clonal propagation. Previous research has had little success in producing viable seed from any controlled pollinations, but clonal material resistant to P. cinnamomi has been produced using tissue culture. The question posed in this thesis was Can we improve breeding and propagation techniques of jarrah? Techniques were developed for testing of in vitro pollen viability and pollen storage, pollination and fertilisation success after controlled pollinations, including determination of stigma receptivity and development of bud isolation techniques using alfoil. The variation in female fertility between genotypes was examined. The use of paclobutrazol was explored as a method of increasing the level of viable seed production in clonal orchard trees. The use of fertiliser as well as the growth retardant was also explored to see if it increased the level of seed production even more. Genetic diversity, genetic differentiation and phylogeny within Eucalyptus marginata were examined using nuclear and chloroplast DNA analysis with Restricted Fragment Length Polymorphisms. While it was first thought that the fertilisation rate was quite low, it was confirmed that the fertilisation rate is similar to other eucalypt species. The zygote abortion rate was quite high in one clone, but one wild tree had a similar seed production rate to other eucalypt species. The zygote and endosperm appeared to be different in the clone and the wild tree observed. The level of seed production was examined in clones and wild trees and it was found that the level was often quite low, particularly in the clones (0 13% in clones, 0 18% in wild trees) in comparison with other Eucalyptus species, and varied between genotypes. The use of a growth retardant such as paclobutrazol may increase the production of viable seed, if it is applied during autumn. The results were inconclusive for the fertiliser/paclobutrazol experiment, since the paclobutrazol was applied during spring which was the worst time of year for increasing seed production. There were differences between genotypes in reaction to both the paclobutrazol and the fertiliser/paclobutrazol. Genetic diversity was moderate in comparison with other Eucalyptus species, and there was a low level of genetic differentiation between populations in the nuclear genome. No differentiation was observed between the morphologically recognised subspecies in the nuclear genome, but differentiation between the populations on the Swan Coastal Plain and populations on the Darling Plateau was seen in the chloroplast genome, indicating that there was historical separation of these two areas. The conclusions arising from this work are that while controlled pollinations are possible in Eucalyptus marginata the clones that were used in these experiments have often behaved differently to the wild trees in the time of anthesis and levels of viable seed production, and in one clone (5J119) the zygote and endosperm nuclei appeared to be very different to the zygote and endosperm nuclei of a wild tree. Further investigation is necessary to see if these differences are related to the low level of seed production observed in the clonal populations. Paclobutrazol may be worth exploring further as a means of increasing seed production. Material to be used for rehabilitation and seed orchards can be collected from a wide area in the main distribution of the species, although trees on the Swan Coastal Plain are distinct from the trees in the main forest area in the chloroplast genome.

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Epaina, Peter. "Identification of Molecular Markers and Quantitative Trait Loci linked to resistance to Vascular Streak Dieback and Phytophthora pod rot of Cacao Theobroma cacao L)." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/10060.

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In Papua New Guinea (PNG), cacao is an important cash crop with an annual production of over 50,000 tonnes of dry beans and generates over $US50 million. More than 80% of the production comes from smallholders. Cacao therefore, provides a significant source of income to the farming communities. Unfortunately, cacao is a very hard crop to grow profitably due to several endemic problems. Among others, Phytophthora Pod Rot (PPR) and Vascular–Streak Dieback (VSD), caused by P. palmivora and Oncobasidium theobromae respectively, are the two main diseases, both of which cause significant crop losses. Planting of cacao varieties resistant to both diseases has been recognised as the most economical approach to sustain production. As such, development of cacao varieties resistant to both PPR and VSD and combined with other desirable traits constitutes one of the main objectives of cacao breeding in PNG. Two Trinitario cacao genotypes; K82 and KA2-101, were developed in PNG. K82 is resistant to PPR but susceptible to VSD while KA2-101 is susceptible to PPR but resistant to VSD. The two genotypes also have several other important agro-economical traits in contrast to each other. In this study, the two cacao genotypes were inter-crossed to provide progeny population to further our understanding on the genetic basis of resistance to the two diseases. The objectives were to 1) Create a progeny population from parents of contrasting characteristics for PPR and VSD and other useful traits, (2) Understand phenotypic segregation patterns for PPR and VSD among the progeny population, (3) Genotype the population using molecular markers to understand genotypic variation, (4) Generate genetic linkage map and (5) Map quantitative trait loci (QTLs) for PPR and VSD traits and identify molecular markers linked to them. vi Crosses between K82 and KA2-101 were made following standard controlled pollination methods. Losses during the process of pollination, pod growth and maturation were determined. Upon ripening, seeds from the pollinated pods were processed and raised in a nursery for 5-6 months. Leaf samples were collected for genetic fingerprinting. The seedlings were then field planted as single trees. Selected genotypes were cloned and tested in a replicated trial. Resistance to PPR was assessed by both artificial inoculation of detached leaf discs and pods and field pod rot. Detached leaf disc test (LDT) was carried out on seedlings in the nursery and later as mature progeny trees while detached pod test (DPT) and natural pod rot in the progeny trees and clones. Resistance to VSD was assessed based on natural infection in the progeny trees and clones. Stability of PPR and VSD reactions between the different assessments and plants types and association between the results of PPR and VSD assessments were determined. The progeny population was genotyped with simple sequence repeats (SSRs) in this study and with single nucleotide polymorphisms (SNPs) from another study and generated genotypic data. Genetic maps of cacao linkage groups were constructed and compared with previous linkage maps. The PPR and VSD phenotypic data and the linkage map were used to locate QTLs for PPR and VSD resistance and identified SSRs and SNPs linked to the QTLs. The QTLs detected were compared with consensus QTL map constructed by Lanaud et al. (2009) from several QTL maps of Phytophthora (P. palmivora, P. megakarya and P. capcisi), witches broom and frosty pod resistance. Significant losses occurred in the process of pollination and pod growth and later as seedlings or trees in the field due to both abiotic and biotic factors. Only about half of the targeted vii progenies was finally established and used. The assessment methods used clearly discriminated the genotypes with different levels of PPR and VSD resistance reactions. Genotypes with resistance levels higher than the resistant parent for PPR or VSD and genotypes resistant to both diseases were identified. The continuum of variations indicated that PPR and VSD resistance are inherited quantitatively, agreeing with previous findings. Thus, breeding for resistance would be an effective means of controlling the two diseases. PPR reactions of same genotypes tested as seedlings, progeny trees and clones by both LDT and DPT indicated weak correlation. However, several individuals consistently maintained their level of reactions across the different plant types and assessment methods. The artificial inoculation tests and field pod rot gave similar results. The findings suggested that cautionary measures should be taken when artificial tests are used for selecting PPR resistance. Similarly, although, the correlation between the VSD and PPR reactions was low, several genotypes consistently maintained their resistant reaction for the two diseases across the different plant types and assessment methods. The PPR and VSD resistance status of the progeny trees and the clones derived from them were generally stable, supporting the clonal breeding advocated in PNG. The genetic fingerprinting revealed DNA variation between the parents. Segregation of the parental alleles of the loci among the progenies followed segregation types expected from crossing between heterozygous parents for SSRs. By employing 716 markers (SSRs and SNPs), a reasonably saturated cacao linkage map was constructed, that had good homology with previous maps. This suggested the reliability and its utility across map based molecular studies. The markers largely clustered in localised regions of the chromosomes, clearly indicating ‘hot’ and ‘cold’ spots for recombination and possibly reflecting some structural or functional properties of the DNA in these parts of the genome. Several loci, which mostly segregated in KA2-101, a self-incompatible parent, deviated from the expected ratios. Higher viii proportion of distorted loci in a self-incompatible parent appears to be common in all cacao mapping populations developed so far, suggesting self-incompatibility as a contributing factor to segregation distortion. Phenotypically, the two Trinitario parents are variable. This was ascertained at the genomic level, with 50% heterozygous across all the SSRs assessed. However, at the chromosomal level, each parent was either highly heterozygous or homozygous for several of the loci in certain chromosomes, indicating fixation or non-fixation of some segments of the chromosomes. The results clearly reflected the dynamics of breeding and selection process of the two parents. QTL analysis detected 31 putative QTLs for the 16 PPR and VSD traits. Most of the QTLs tended to be localised in certain regions of only few chromosomes. Moreover, in most cases, the PPR and VSD QTLs on the same chromosome were located in the same region and corresponded to the Phytophthora QTLs in the same regions and/or ‘hot spots’ of each chromosome in the consensus QTL map. In several LGs, the PPR and VSD QTLs were located in the same region as the QTLs for witches’ broom and frosty pod resistance. The results supported previous findings that localized regions or ‘hotspots’ for QTLs for Phytophthora resistance exist in cacao genome. Moreover, detection of VSD QTLs in the same ‘hot spots’, indicated their localized and co-existence with QTLs for Phytophthora resistance. Progenies resistant to both the PPR and VSD suggested that the co-located PPR and VSD QTLs may have been inherited together. However, whether the QTLs are the same or not need to be verified. Furthermore, the location of Phytophthora and VSD QTLs in the same region with the Bitches’ Broom and Frosty Pod may also indicate the involvement of common or a cluster of genes conferring resistance to the fungal diseases in cacao. The percentage phenotypic variation explained by each QTL suggested low to intermediate ix effects. Similar findings have been reported in most QTL studies for Phytophthora resistance and suggest that a large number of genes having small effects may be involved in the resistances to PPR and VSD. This is further supported by the polygenic nature of resistance with additive effects that have been reported for PPR and VSD. Higher allelic effects of the resistant parents were largely contributing to the resistance QTLs. However, mixed allelic effects of the parents for the QTLs were evident. This suggested that susceptible genotypes can also be a source of genetic variability for disease resistance, which is not commonly exploited in conventional breeding programs because their phenotypic contributions are considered too weak. However, the use of molecular markers could facilitate an exhaustive detection and the management of such traits. SSRs and SNPs linked to the QTLs for PPR and VSD traits were identified. Moreover, distance between the flanking markers for all the QTLs identified were less than 5 cM, suggesting that use of high density maps based on SNPs would greatly narrow down the QTLs regions and identify SNPs, which are more targeted to the functional genes to increase the efficiency of marker assisted selection (MAS) program in cacao. SSRs and SNPs identified in this study, are potential markers to be employed for MAS program in developing resistant varieties to reduce the effects of, not only P. palmivora and VSD but other Phytophthora diseases. Moreover, location of the PPR and VSD QTLs in the same regions as the QTLs for other Phytophthora species, Witches’ Broom and Frosty Pod resistance also offer the possible accumulation of the different genes for the different diseases to improve and sustain the durability of disease resistance in cacao. It also offers the possibility of developing common markers for the diseases for MAS, so that selection for one disease can provide opportunities for selection for other diseases.

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Foggo, Andrew. "The biology and ecology of the ash bud moth Prays fraxinella Bjerk. with special reference to its role in the dieback of hedgerow ash trees." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314876.

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Safodien, Sieyaam. "The molecular identification and characterisation of Eutypa dieback and a PCR-based assay for the detection of Eutypa and Botryosphaeriaceae species from grapevine in South Africa." Thesis, Stellenbosch : Stellenbosch University, 2007. http://hdl.handle.net/10019.1/21757.

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Thesis (MSc)--University of Stellenbosch, 2007.
ENGLISH ABSTRACT: Grapevine trunk diseases are caused by invasive pathogens that are responsible for the slow decline of vines. In particular, Eutypa dieback of grapevine has had a devastating impact on vineyards worldwide, reducing growth and yield, eventually killing the grapevine. The causal organism of Eutypa dieback was first described as Eutypa armeniacae Hansf. & Carter, the pathogen that causes dieback of apricots, but since 1987 this species has been considered a synonym of Eutypa lata (Pers.:Fr.) Tul & C. Tul (anamorph Libertella blepharis A. L. Smith). Recently, it was proposed that at least two species that are capable of infecting grapevines are responsible for Eutypa dieback. Consequently, the molecular identification and characterisation of Eutypa dieback was used to delineate the species occurring on infected grapevines in South Africa. This involved the molecular analyses of three molecular markers, namely, the internal transcribed spacer (ITS) and large subunit (LSU) regions of the ribosomal DNA operon, and the -tubulin gene. The results obtained revealed the presence of a second species, namely, Eutypa leptoplaca (Mont.) Rappaz, that occurred together with E. lata on infected grapevines. Also co-habiting with these pathogens were related fungi form the Diatrypaceae family, Cryptovalsa ampelina (Nitschke) Fuckel and Eutypella vitis (Schwein.) Ellis & Everhart. Pathogenicity tests conducted on isolates representing C. ampelina, E. lata, E. leptoplaca, and E. vitis revealed that all were pathogenic to grapevine. Several species of Botryosphaeriaceae that commonly invade the woody tissue of grapevines are also pathogenic to grapevine. The symptoms in grapevine commonly associated with Botryosphaeriaceae are easily confused with the symptoms produced by Eutypa dieback which prompted the need for the development of a detection method that can correctly identify the presence of multiple pathogens. A reverse dot blot hybridisation (RDBH) method was subsequently applied to provide a rapid, accurate and reliable means of detecting the Eutypa species involved in the Eutypa disease complex, as well as those species of Botryosphaeriaceae known to cause disease in grapevines. The method involved the use of multiplex PCR to simultaneously amplify and label the regions of DNA that are used as pathogen specific probes. Consequently, membrane immobilised species-specific oligonucleotides synthesised from the ITS, - tubulin and LSU molecular data were evaluated during the application of this diagnostic method to detect Eutypa species. It was found that the species-specific oligonucleotides, designed from ITS sequence data, could consistently detect E. lata and E. leptoplaca. The application of the RDBH method for the detection of these Eutypa species, based on -tubulin and LSU sequence data, however, proved to be unsuccessful. Subsequently, a RDBH method, utilising species-specific oligonucleotides designed from elongation factor-1α sequence data, was successfully applied for the detection of Botyrosphaeria dothidea (Moug.:Fr.) Ces. & De Not., Neofusicoccum luteum (Pennycook & Samuels) Crous, Slippers & A.J.L. Phillips, Neofusicoccum parvum (Pennycook & Samuels) Crous, Slippers, A.J.L. Phillips and Neofusicoccum ribis (Slippers, Crous & M.J. Wingf.) Crous, Slippers & A.J.L. Phillips. The method, however, was unsuccessful for the detection of Diplodia seriata De Not. In addition to the above-mentioned shortcomings, the RDBH was not amenable to the detection of pathogens directly from field or environmental samples, but required preparation of DNA from pure cultures. The method, however, allows for the identification of multiple pathogens in a single assay. As DNA extraction methods are amended, improved and honed to obtain DNA from environmental samples, so would it increase the usefulness of RDBH.
AFRIKAANSE OPSOMMING: Wingerd stamsiektes word veroorsaak deur patogene wat die vermoë het om wingerdplante te infekteer en dan stadige agteruitgang van dié wingerde te veroorsaak. Veral Eutypa terugsterwing het ‘n vernietigende effek op wingerde wêreldwyd deurdat dit groeikrag en oesmassa verlaag, maar ook omdat dit uiteindelik wingerdstokke kan dood. Die veroorsakende organisme is aanvanklik as Eutypa armeniacae Hansf. & Carter beskryf, die patogeen wat terugsterf by appelkose veroorsaak, maar sedert 1987 word hierdie spesies beskou as ‘n sinoniem van Eutypa lata (Pers.:Fr.) Tul & C. Tul (anamorph Libertella blepharis A. L. Smith). Dit is egter onlangs voorgestel dat ten minste twee spesies die vermoë het om wingerd te infekteer om Eutypa terugsterwing te veroorsaak. Gevolglik is molekulêre identifikasie- en karakteriseringstudies geloods om te bepaal watter spesies Eutypa terugsterwing in Suid-Afrikaanse wingerde veroorsaak. Dit het die molekulêre analise van drie molekulêre merkers behels, naamlik die interne getranskribeerde spasiëerderarea (“ITS”), die groot ribosomale subeenheid (“LSU rDNA”) en β-tubilien geen. Resultate van die filogenetiese analise dui daarop dat ’n tweede spesies, naamlik Eutypa leptoplaca (Mont.) Rappaz, saam met E. lata in geïnfekteerde plante voorkom. Saam met bogenoemde twee spesies het daar ook verwante spesies van die Diatrypaceae familie voorgekom, naamlik Cryptovalsa ampelina (Nitschke) Fuckel en Eutypella vitis (Schwein.) Ellis & Everhart. Patogenisiteitstudies wat uitgevoer is met verteenwoordigende isolate van C. ampelina, E. lata, E. leptoplaca, en E. vitis dui daarop dat almal patogene van wingerd is. Verskeie Botryosphaeriaceae spesies wat gereeld in houtagtige wingerdweefsel aangetref word, is ook patogene van wingerd. Interne simptome wat algemeen met Botryosphaeriaceae infeksies geassosieer word, kan baie maklik met dié van Eutypa terugsterwing verwar word en dit het die nood laat ontstaan om ‘n opsporingsmetode te ontwikkel wat akkuraat genoeg is om tussen veelvoudige infeksies te onderskei. ’n Omgekeerde-stippelklad-hibridisasie (OSH) metode is gevolglik aangewend om Eutypa spesies betrokke in die Eutypa-siektekompleks op ‘n vinnige, akkurate en betroubare manier op te spoor, sowel as die Botryosphaeriaceae species wat bekend is as patogene van wingerd. Die metode behels ’n saamgestelde PKR vir die vermeerdering en merk van DNS areas wat gebruik word as patogeen spesifieke peilers. Spesies-spesifieke oligonukleotiede ontwikkel vanaf die ITS, -tubilien en LSU molekulêre data is op ‘n membraan vasgeheg en gebruik om ’n diagnostiese toets te ontwikkel vir Eutypa species. Merkers ontwikkel vanaf die ITS kon E. lata and E. leptoplaca konsekwent opspoor. Die opspoor van Eutypa spesies met merkers vanaf die -tubulien en LSU gene met OSH was onsuksesvol. Die OSH metode met merkers vanaf die verlengingsfaktor-1α kon susksesvol gebruik word om Botyrosphaeria dothidea (Moug.:Fr.) Ces. & De Not., Neofusicoccum luteum (Pennycook & Samuels) Crous, Slippers & A.J.L. Phillips, Neofusicoccum parvum (Pennycook & Samuels) Crous, Slippers, A.J.L. Phillips and Neofusicoccum ribis (Slippers, Crous & M.J. Wingf.) Crous, Slippers & A.J.L. Phillips op te spoor. Dié metode kon egter nie Diplodia seriata De Not. opspoor nie. Bykomend tot bogenoemde tekortkominge, kon die omgekeerde-stippelklad-hibridisasie metode ook nie aangepas word om patogene direk vanuit plantmateriaal op te spoor nie en word DNS afkomstig vanaf suiwer kulture benodig. Dié metode laat egter identifikasie van verskeie patogene in ‘n enkele toets toe. Soos DNS ekstraksie metodes aangepas, verbeter en verfyn word om DNS vanuit plantmateriaal te verkry, sal die bruikbaarheid van die omgekeerde stippelklad hibridisasie metode ook verbeter.

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Needham, Jessica. "Harnessing demographic data for cross-scale analysis of forest dynamics." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:156850fa-3148-45a6-b2f8-ada9dd3f6a7f.

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Forests are a critical biome but are under threat from unprecedented global change. The need to understand forest dynamics across spatial, temporal and biological scales has never been greater. Critical to this will be understanding how the demographic rates of individuals translate into patterns of species diversity, biomass and carbon turnover at much larger scales. In this thesis, I present a modelling framework focussed on demography. In Chapter 2, I introduce methods for translating forest inventory data into population models that account for the size-dependency of vital rates and persistent differences in individual performance. Outbreaks of forest pest and pathogens are increasing in frequency and severity, with consequences for biodiversity and forest structure. In Chapter 3, I explore the impact of ash dieback on the community dynamics of a British woodland, describing a spatially explicit individual based model that captures the effect of an opening of the canopy on local competitive interactions. Chapter 4 introduces methods to infer the impact of historical deer herbivory on the juvenile survival of forest trees. The approach is generalisable and could be applied to any forest in which patterns of regeneration and community structure have been impacted by periodic disturbance (e.g. forest fires). Finding meaningful ways of incorporating species diversity into global vegetation models is increasingly recognised as a research priority. In Chapter 5, I explore the diversity of demographic rates in a tropical forest community and identify groups of species with similar life history strategies. I discuss the potential of integrating demographic and physiological traits as a way to aggregate species for inclusion in global models. In summary, translating measurements of individuals into population dynamics provides opportunities to both explore small-scale community responses to disturbance events, and to feed into much larger scale vegetation models.

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Horn, Kevin Paul. "An Investigation of the Role of Macrophages in Spinal Cord Injury and Repair." Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1249267954.

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Garms, Mareike [Verfasser], Hubert [Akademischer Betreuer] Job, Marius [Gutachter] Mayer, and Hubert [Gutachter] Job. "Perception of climate-induced forest dieback and silvicultural adaptation to climate change in mountain forests - The case of the Bavarian Forest / Mareike Garms ; Gutachter: Marius Mayer, Hubert Job ; Betreuer: Hubert Job." Greifswald : Universität Greifswald, 2021. http://d-nb.info/1234149192/34.

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Filous, Angela R. Ph D. "The Role of NG2+ Cells in Regeneration Failure After Spinal Cord Injury." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1396605992.

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Bortolami, Giovanni. "Impact des agents pathogènes sur le bilan hydrique et carboné de la vigne : conséquences pour le dépérissement de la vigne." Thesis, Bordeaux, 2021. http://www.theses.fr/2021BORD0114.

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Au cours de leur vie les plantes pérennes sont confrontées à plusieurs stress en interaction qui les entrainent dans un processus de dépérissement. Ces interactions, et leurs changements par rapport aux conditions climatiques et à l’état physiologique de la plante, sont fondamentales pour la compréhension du processus de dépérissement. Malgré l’augmentation des évènements de dépérissement à l’échelle mondiale, les connaissances sur ces mécanismes restent limitées, étant données les difficultés techniques rencontrées dans l’étude des interactions complexes. Dans cette thèse nous avons étudié l’interaction entre deux stress fréquemment vécus par la vigne : la sècheresse et une maladie vasculaire, le mal d’esca. L’esca est une maladie qui soulève plusieurs hypothèses sur sa pathogénèse. Une des principales hypothèses est que les symptômes foliaires et la mort de ceps de vigne soient causés par un dysfonctionnement hydraulique dans les vaisseaux du xylème. Pour cette raison, la sècheresse pourrait contribuer en synergie avec l’esca au dépérissement de la vigne. Compte tenu de ce contexte, nous avons tout d’abord exploré l’hypothèse de dysfonctionnement hydraulique pendant la pathogenèse de l’esca. Nous avons mis en évidence que pendant l’expression des symptômes foliaires plusieurs organes sont atteints par un dysfonctionnement hydraulique qui cause en moyenne une perte de conductivité hydraulique de 69% sur les nervures centrales des feuilles, 55% sur les pétioles et 30% sur les tiges. Contrairement à l’embolie gazeuse classiquement observée pendant la sècheresse, le dysfonctionnement hydraulique pendant l’esca est causé par la présence d’occlusions vasculaires (thylloses et gels) produites par la plante. Après cette découverte, nous avons exploré l’interaction entre l’esca et la sècheresse, en imposant une contrainte hydrique aux plantes naturellement infectées. Nous avons découvert que la sécheresse inhibait complètement l’expression des symptômes d’esca, étant donné qu’aucune plante en stress hydrique (à ΨPD ≈ -1MPa pour trois mois) n’a montré de symptômes foliaires pendant deux saisons consécutives. Nous avons également étudié les relations hydriques et carbonées, à l’échelle de la plante entière au cours de ces expérimentations. Nos résultats soulignent un fonctionnement physiologique distinct lorsque la vigne est soumise à une sécheresse ou exprime des symptômes d’esca. L’esca (et la baisse de la conductance stomatique associée) n’est pas causé par une chute de potentiel hydrique, et génère des dynamiques saisonnières différentes de la sécheresse au regard des échanges gazeux et des teneurs en carbohydrates non-structuraux. Cette thèse souligne l’importance d’identifier les seuils physiologiques sous-jacents aux différentes interactions entre facteurs pendant le processus de dépérissement des plantes. Dans l’ensemble, ces résultats ouvrent des nouvelles perspectives scientifiques et agronomiques pour les interactions plante-pathogène-environnement et pour la durabilité des vignobles
Perennial plant dieback is an increasing and complex phenomenon. Perennial plants experience many interacting stressing events leading to final plant mortality. These interactions, and how they may change regarding climatic conditions and plant physiological status, are key in understanding the dieback process. Although dieback events are increasing worldwide, the knowledge on the dieback mechanisms are scarce, given the many technical challenges in studying complex interactions. In this thesis, we studied the interaction between two stresses frequently experienced by grapevines, one of the most important perennial crops: drought and esca (a vascular disease). Esca is a disease in which there are many competing hypotheses regarding its pathogenesis. One of the main hypothesis is that leaf symptoms and plant death are caused by hydraulic failure in xylem vessels. For this reason, drought is thought to contribute synergistically with esca to grapevine dieback. In this context, this thesis has primarily explored the hydraulic failure hypothesis during esca pathogenesis. We found that during leaf symptom expression both leaves and stems suffer from hydraulic failure causing (on average) 69% loss of hydraulic conductance in midribs, 55% in petioles, and 30% in stems. Differing from classical air embolism during drought, we observed that hydraulic failure during esca was caused by the presence of plant-derived vascular occlusions (i.e. tyloses and gels) produced at a distance from the pathogen niche in the trunk. After this discovering, we explored the interaction between esca and drought, subjecting naturally infected plants to drought. We found that drought totally inhibits esca leaf symptoms, as none of the plants under water deficit (at ΨPD ≈ -1MPa for three months) expressed leaf symptoms in two consecutive seasons. At the same time, in order to understand the interaction between esca and drought, we recorded the whole-plant water relations and carbon economy of grapevine under both stresses. We highlight the distinct physiology behind these two stresses, indicating that esca and drought present different underlying mechanisms, and induce different plant responses and physiological consequences. Esca (and subsequent stomatal conductance decline) does not result from decreases in water potential, and generates different gas exchange and non-structural carbohydrate seasonal dynamics compared to drought. Finally, we observed that esca affected the recorded plant physiology only seasonally, and not over the long-term. This thesis highlights the importance in finding the physiological thresholds triggering the different interactions during plant dieback. Together, the results open new scientific and agronomical perspectives on plant-pathogen-environment interactions and vineyard sustainability

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Semizer, Cuming Devrim [Verfasser], Reiner [Akademischer Betreuer] Finkeldey, Oliver [Gutachter] Gailing, and Kurt [Gutachter] Weising. "Gene flow from planted common ash (Fraxinus excelsior L.) stands to old-growth forests – implications for conservation and use of genetic resources affected by ash dieback / Devrim Semizer Cuming ; Gutachter: Oliver Gailing, Kurt Weising ; Betreuer: Reiner Finkeldey." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2018. http://d-nb.info/1173975039/34.

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Björkroth, Jennie. "Effekter av naturvårdsgallring på förekomsten av lunglav på ädellövträd." Thesis, Linköpings universitet, Biologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-120089.

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Sun-exposed broad leaved deciduous trees have a great species diversity of epiphytic lichens. In Europe, these trees have decreased dramatically in number as wooded pastures have become overgrown with trees and bushes, and broad leaved deciduous stands have been replaced by planted coniferous trees. These are the main reasons for many lichens depending on deciduous trees being red-listed. Epiphytic lichens in overgrown areas could benefit from conservation thinning, but few studies have been performed on how this type of cutting affects the lichens. In a previous study, the presence of red-listed epiphytic lichens in a broad leaved deciduous forest was examined. After the study, thinning of trees and bushes was made. Here we study the effects of this thinning on Lobaria pulmonaria. We tested possible factors that may affect the growth of L. pulmonaria, and if there were any differences in incidence and vitality of the lichen between managed and unmanaged stands. Since Dutch elm disease and ash dieback are well spread in the area, we wanted to see if they also affected the growth of L. pulmonaria. There were no differences in incidence and growth between managed and unmanaged stands. The results were unexpected since other studies show that, for instance, increased sun exposure often has a great effect on the growth of lichens. Many elms and ashes were dead or dying and had a significant negative effect on the change of number of lobes and the lobe surface. The diseases of the trees can thus be assumed to be the greatest cause of why the lichens in the managed stand did not benefit from thinning.

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Woltjen, Christine D. "Responding to industry needs from the field to the greenhouse: Dieback and cankers of Gleditsia triacanthos var. inermis and characterization of an Ohio isolate of Melon necrotic spot virus and its vector, Olpidium bornovanus, collected from Cucumis sativ." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1276549930.

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47

George, Amy Kathryn. "Eucalypt regeneration on the Lower Murray floodplain, South Australia." Connect to this title online, 2004. http://hdl.handle.net/2440/37706.

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Vegetation along the River Murray floodplains has been shown to be in a severe state of decline. This decline is amplified by the impositions of river regulation. In South Australia, where vegetation losses have been great, regeneration is limited and may result in not only individual tree losses but also widespread population decline. This study aimed to examine the relationship between river flows and the regeneration process in populations of Eucalyptus camaldulensis and Eucalyptus largiflorens. The current structure of the populations was examined to determine if a viable number of varying age-classed trees were present. Tree surveys conducted at Banrock Station determined that while densities were low for both species, E. camaldulensis had a more sustainable population structure than E. largiflorens. Growth stages for both species illustrated highly clumped distribution, which is believed to correspond with river flooding magnitudes and frequencies. To address the potential link between tree distribution and flooding within the River Murray, a hydrological analysis was conducted for Banrock Station using river flows at the South Australian border from 1900 to 2003. The amount of time growth stages for each species were inundated was found to be greatly reduced under regulated flows compared to natural flows. This has resulted in shifted localized regeneration patterns corresponding with E. camaldulensis' greater demand for inundation than E. largiflorens. Moderate magnitude flows have been most impacted by regulation, and consequently these are the very flows needed for floodplain tree population maintenance. Flowering and seed fall for E. camaldulensis and E. largiflorens were monitored at Banrock Station for 22 months to identify losses in reproductive potential resulting from tree decline. While seed viability was not affected by vigour, trees with visually reduced vigour were found to produce less fruit and had reduced seed fall, as well as a reduced rate of fruit development. Dendrochronological techniques were applied to floodplain trees. Age and size relationships could be established, implying that such techniques can be applied in South Australia to high quality sites. Growth responses within cohorts were similar and easily matched between individuals illustrating cyclic, but not necessarily seasonal correlations. This work verified the preferential selection of younger trees for dendroecological studies, and identified a relationship between on moderate flows and measurable girth expansion in both floodplain tree species.
Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2004.

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Ben, M'henni Yosra. "Gestion de la maladie de dépérissement du pommier : criblage in vitro et in planta des activités protectrices d’une collection de microorganismes contre les Pythiacées et caractérisation chimique du principal actif produit par l’isolat A. westerdijkiae A7 Biocontrol and growth promotion potential of combined application of Trichoderma simmonsii and Aspergillus westerdijkiae in Apple root stock dieback." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS127.

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Le dépérissement du pommier est une maladie tellurique causée par plusieurs espèces Pythiacée. Il est responsable de graves dommages et de pertes d'arbres dans de nombreux vergers en Tunisie. Comme la lutte chimique contre cette maladie pose des problèmes éco toxicologiques et les moyens prophylactiques ont des efficacités limitées, d’autres moyens de lutte sont activement recherchés. L’objectif de cette thèse était d’identifier un nouvel agent de lutte biologique contre les oomycètes responsables de cette maladie à partir d’une collection d’isolats fongiques et bactériens Tunisiens comme alternative au contrôle chimique. Les isolats fongiques étudiés appartenaient aux genres Trichoderma, Aspergillus et Penicillium spp., les isolats bactériens appartenaient au genre Bacillus spp. clade subtilis. Les isolats fongiques ont fortement inhibé la croissance in vitro des Pythiacées (> 40%) par rapport aux isolats bactériens ; en particulier, les filtrats de culture des isolats A. westerdijkiae A7 et T. simmonsii A2. L'évaluation de l’activité préventive et curative contre les Pythiacées sur des porte-greffes du pommier de ces deux isolats fongiques et de la souche Bacillus B2 a montré que T. simmonsii A2 était le plus efficace lorsqu'il était appliqué à titre préventif. De même, la combinaison de la souche Bacillus B2 et de l’isolat A. westerdijkiae A7 a induit une bonne protection contre les Pythiacées en préventif. La combinaison des isolats T. simmonsii A2 et A. westerdijkiae A7 a entraîné une meilleure protection en traitement curatif, alors que la combinaison des trois isolats ensemble réduisait fortement l’activité protectrice. Notre étude révèle le potentiel des isolats Tunisiens, seuls ou en combinaison, en tant qu'agents de lutte biologique contre le dépérissement du pommier ainsi qu'un effet bénéfique supplémentaire sur la croissance végétale observé au niveau des racines et de la longueur des tiges. Ainsi, nous avons sélectionnés les meilleurs candidats agissant par antibiose pour l'identification des principaux agents actifs responsables de l'activité anti-oomycète. L'isolat A. westerdijkiae A7 a été retenu avec 100% d'inhibition de la croissance mycélienne des isolats de Pythiacées testés. Plusieurs étapes de purification successives du filtrat de culture ont permis d’identifier l'acide pénicillique (acide 3-méhoxy-5-méthyl-4-oxo-2,5-hexadiénoïque) en tant que principale molécule responsable de l’inhibition la croissance mycélienne des Pythiacées testées. Étant donné que l’acide pénicillique possède des propriétés toxiques pour la santé humaine et animale, l’isolat A. westerdijkiae A7 ne pourra pas être utilisé en tant que BCA puisqu’il produit cette mycotoxine malgré nos résultats prometteurs in planta. L’ensemble de ces travaux montre le potentiel anti-oomycète des micro-organismes in vitro qui peut différer de l’activité protectrice contre les Pythiacées in planta. Ils révèlent également la nécessité de caractériser l’ingrédient actif pour les études de toxicité nécessaire au développement d’un produit de bio-contrôle
Apple dieback is a telluric disease caused by several Pythiaceae species. It is responsible for serious damage and loss of trees in many orchards in Tunisia. As the chemical control of this disease poses eco-toxicological problems and the prophylactic means have limited effectiveness, other means of fight are actively sought. The objective of this thesis was to identify a new biological control agent against oomycetes responsible for this disease from a collection of Tunisian fungal and bacterial isolates as an alternative to chemical control. The fungal isolates studied belonged to the genera Trichoderma, Aspergillus and Penicillium spp., The bacterial isolates to the genus Bacillus spp. clade subtilis. Fungal isolates strongly inhibited the growth of Pythiaceae in vitro (> 40%) compared to bacterial isolates; in particular, the culture filtrates of isolates A. westerdijkiae A7 and T. simmonsii A2. The evaluation of the preventive and curative activity against Pythiaceae on apple rootstocks of these two fungal isolates and of the Bacillus B2 strain showed that T. simmonsii A2 was the most effective when applied preventively. Likewise, the combination of the Bacillus B2 strain and the A. westerdijkiae A7 isolate induced good protection against Pythiaceae as a preventive measure. The combination of the T. simmonsii A2 and A. westerdijkiae A7 isolates resulted in better protection in curative therapy, while the combination of the three isolates together greatly reduced the protective activity. Our study reveals the potential of Tunisian isolates, alone or in combination, as biological control agents against apple dieback as well as an additional beneficial effect on plant growth observed at the level of the roots and the length of the stems. Thus, we have selected the best candidates acting by antibiosis for the identification of the main active agents responsible for anti-oomycete activity. The A. westerdijkiae A7 isolate was retained with 100% inhibition of mycelial growth of the Pythiaceae isolates tested. Several successive purification steps of the culture filtrate made it possible to identify penicillic acid (3-mehoxy-5-methyl-4-oxo-2,5-hexadienoic acid) as the main molecule responsible for inhibiting growth mycelia of the Pythiaceae tested. Since penicillic acid has toxic properties for human and animal health, isolate A. westerdijkiae A7 cannot be used as BCA since it produces this mycotoxin despite our promising results in planta. All of this work shows the anti-oomycete potential of microorganisms in vitro, which may differ from the protective activity against Pythiaceae in planta. They also reveal the need to characterize the active molecule for the toxicity studies necessary for the development of a biocontrol product

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Salowi, Asmah. "Towards biological control of Pistachio dieback." Thesis, 2010. http://hdl.handle.net/2440/63478.

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Xanthomonas translucens (Xtp) causes dieback disease of pistachio in Australia. The bacterium infects the vascular tissues of the trees, causing discolouration of the xylem, lesions on the trunk and major limbs, decline and, in some cases, death. Although hygiene and application of quaternary ammonium disinfectant to pruning wounds have been recommended to limit the spread of the disease, effective control methods are lacking. Biological control offers potential in managing this disease. The aims of this research were to assess the ability of selected bacteria to antagonise Xtp and to evaluate the ability of the synthetic peptide BP100 to suppress growth of Xtp in liquid medium. Isolate KI of X. translucens (DAR75532), obtained from a commercial pistachio orchard in Kyalite (NSW) was used. The potential antagonists comprised one isolate of Bacillus subtilis and several bacteria isolated from pistachio wood and stored following indications of ability to inhibit Xtp. Preliminary screening of the potential antagonists was conducted by means of an agar diffusion assay, in sucrose peptone agar (SPA) and nutrient agar (NA). Inhibition of growth of DAR75532 varied among bacterial isolates and with the culture medium used. Generally, the isolates produced larger inhibition zones on SPA than on NA and appeared to be bacteriostatic. When diffusible compounds were extracted from liquid cultures through centrifugation and filtration, there was no evidence of antibiotic activity. Further experiments demonstrated that two antagonists produced antibacterial metabolites in liquid medium. In contrast, culture filtrate of isolate 64161-7 grown in nutrient broth supplemented with yeast extract and glucose inhibited DAR75532, and filtrate from isolate PC397 grown in the same medium, or in nutrient broth supplemented with yeast extract and nutrient broth alone, was inhibitory. However, the antibiotic effect of PC397 was lost as the cell free culture filtrate was diluted. Competition was also identified as a possible mechanism, as DAR75532 was not recovered on SPA when mixed with isolates 64161-17, SUPP, B. subtilis, PC397, PC506 or PC507. An in vitro assay was developed to evaluate the ability of the potential antagonists to reduce colonisation of pistachio wood by DAR75532. The pathogen, antagonists 64161L and PC397, or pathogen plus antagonists were vacuum-infiltrated into non-autoclaved excised pistachio twigs, before incubating for 10 days. The pathogen and antagonists were recovered from the middle section of the wood, following soaking in saline and plating suspensions on SPA and NA supplemented with cephalexin, ampicillin and gentomicin (NA+ab). The antagonists were recovered and grew well on SPA but not NA+ab, indicating that they survived in pistachio wood. The pathogen was recovered on NA+ab and SPA, although indigenous wood-inhibiting bacteria also grew on SPA. Only PC397 was recovered from twigs inoculated with PC397 plus DAR75532. This suggested that PC397 inhibited colonisation of pistachio wood by the pathogen. Peptide BP100 was obtained from the University of Girona, Spain. A turbidimetric-based system was first used to monitor the effect of BP100 on growth of DAR75532 over time. Multiplication of DAR75532 in sucrose peptone broth (SPB) was delayed or reduced in the presence of BP100. At low concentration, the peptide was bacteriostatic and DAR75532 colonies were subsequently recovered on SPA. Higher concentrations were bactericidal. To verify bactericidal activity, suspensions of DAR75532 treated with peptide were sampled over time and the colony forming units enumerated on SPA and compared with untreated controls. The minimum inhibitory (bacteriostatic) or bactericidal concentration of BP100 was influenced by the initial concentration of DAR75532 and by incubation time. Peptide at 2.5 μM was sufficient to inhibit growth of DAR75532 in SPB when the initial concentration was 10⁶ CFU/ml, but a minimum of 5 μM was required to kill the cells. The mortality of DAR75532 three hours after treatment was 77.35% when 5 μM of peptide BP100 was applied. Preliminary screening had identified isolate 64161-7 as having potential to inhibit DAR75532. The isolate was tentatively identified as Pseudomonas tolaasii, P. fluorescens or P. putida by the National Collection of Plant Pathogenic Bacteria (UK). Although this isolate survived well in excised twigs of pistachio, it did not prevent colonisation of the wood by DAR75532. However, PC397, likely to be a Bacillus sp., reduced colonisation by DAR75532. The other six potential antagonists remain to be tested on pistachio wood. The effect of medium composition, such as sugar content, on antibiotic production should also be investigated. In addition, peptide BP100 offers promise as a means of controlling pistachio dieback. The ability of the bacterial isolates and the peptide to reduce colonisation of DAR75532 in pistachio trees should be assessed in a natural system where the influence of other factors can be evaluated.
Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 2010.

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50

Chakraborty, Tanmoy. "Multi-scale assessment of drought-induced forest dieback." Master's thesis, 2020. http://hdl.handle.net/10362/94403.

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Dissertation submitted in partial fulfilment of the requirements for the degree of Master of Science in Geospatial Technologies
Drought has been intensified over the years and will continue to worsen due to climate change. Existing works have focused their attention on crops rather than forests. Adverse effects are felt by all flora and fauna but the impact of the recent droughts on forest ecosystems is still unknown. Greater root depth allows them to withstand the immediate impacts of drought in contrast to crops and other vegetation. This study aims to see not only the interaction between drought and forest vitality from a multi-scale and temporal viewpoint while also to detect the impact of the recent 2018/19 drought on forest vitality based on remote sensing data. The data from the German Drought Monitor was used for the area-wide estimation of drought in Germany. Vegetative indices like NDVI collected from MODIS and Sentinel 2A were used to study the interactions between drought and forest vitality. Data for both have been acquired for the years 2000-2019. A long-standing time series data was decomposed and seasonally adjusted for better cross-correlation between the variables. The cross-correlation was verified by using breakpoints estimation by dividing the data into historically observed and test data. The coniferous-dominated black forest was used as a study area for a more in-depth analysis. Results showed that forest vitality was lowest one month after a severe drought, indicated by the highest decline in NDVI for all the forest types. This was verified using high resolution Sentinel images and the highest change does correspond to the month of January 2019. There was change in NDVI of over -0.5 for 80.63% of the entire study area. The change for each forest type was 81.74%, 54.42%, 84.14% for coniferous, broadleaved and mixed forests respectively. Two decades of NDVI and Soil Moisture Index (SMI) data along with Sentinel images for better area calculation because of higher resolution make this a highly effective approach to assess the impacts of drought on forest dieback. The methodology and data can be applied across the study area and with suitable drought indices can be used to assess the drought induced forest dieback across the globe. However, in-situ analysis with ecological considerations at the individual level could further the validity of the cross-correlations among forest types and drought. Reproducibility self-assessment (https://osf.io/j97zp/): 3, 2, 3, 1, 3 (input data, pre-processing, methods, computational environment, results).

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