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1
Mullins, P. J. "Protoplasts from Phytophthora." Thesis, University of Liverpool, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381366.
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2
Renfrow, Crystal. "Phytophthora in Arizona Citrus." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 1995. http://hdl.handle.net/10150/622384.
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3
Antelo, Luis. "Glucan synthase of Phytophthora sojae." Diss., lmu, 2002. http://nbn-resolving.de/urn:nbn:de:bvb:19-12301.
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4
Chambers, Susan M. "Phytophthora root rot of chestnut /." Title page, contents and abstract only, 1993. http://web4.library.adelaide.edu.au/theses/09PH/09phc4449.pdf.
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5
Smith, Christine E. "The genetics of Phytophthora infestans." Thesis, Bangor University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357832.
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6
Harrison, Brenda Jean. "The genetics of Phytophthora infestans." Thesis, Bangor University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278736.
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7
Finlay, Annabelle Ruth. "Microbial suppression of Phytophthora cinnamomi." Thesis, Queen's University Belfast, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317116.
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8
Permanandani, Jagdish Assandas. "Somatic variations in Phytophthora drechsleri." Thesis, University of Liverpool, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291879.
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9
Khaliq, Ihsanul. "Range expansion of Phytophthora, particularly Phytophthora cinnamomi into colder environments: adaptation, a changing environment or both?" Thesis, Khaliq, Ihsanul (2019) Range expansion of Phytophthora, particularly Phytophthora cinnamomi into colder environments: adaptation, a changing environment or both? PhD thesis, Murdoch University, 2019. https://researchrepository.murdoch.edu.au/id/eprint/43119/.
Full textAbstract:
Alpine and sub-alpine regions were long considered free of Phytophthora species, especially Phytophthora cinnamomi due to restrictions on their growth from low temperatures. However, P. cinnamomi was isolated from a sub-alpine area ‘Barrington Tops National Park’ in the 1990s. Subsequent Australia wide surveys detected 68 Phytophthora species in Australia. Of these, 33 Phytophthora species, including P. cinnamomi, were detected in the alpine and sub-alpine areas on Kosciuszko National Park (KNP) alone. This suggested that Phytophthora species had adapted to cold environments. This project investigated the ability of Phytophthora species to produce infective propagules (zoospores) and cause disease at increasingly lower temperatures. Phytophthora cinnamomi was selected as a ‘test’ species due to its national and international significance. Initially, preliminary surveys were conducted in the sub-alpine and alpine areas of KNP and Tasmania to obtain living Phytophthora isolates. The lower temperature limit for growth and sporulation of Mediterranean (one isolate was from a sub-alpine area) P. cinnamomi isolates was determined and phenotypic plasticity experiments were established in an attempt to ‘train’ them to produce infective propagules and cause disease at increasingly lower temperatures. Finally, the distribution patterns of Phytophthora and vascular plants species in relation to disturbance and elevation were determined across elevation gradients in KNP. Preliminary surveys resulted in the isolation of eight Phytophthora species, including two new species that were formally described. Phytophthora cinnamomi was shown to produce infective propagules at temperatures lower (7.5 °C) than originally established (10 °C), and in a shorter time compared to original isolates when ‘trained’ under cold conditions. This suggests that P. cinnamomi responds rapidly to selection pressure and adapts to new environments. Although P. cinnamomi produced infective propagules at 7.5 °C, the pathogen could not be isolated from plants grown at 7.5 °C after three months. Therefore, more work is required to establish disease development at 7.5 °C and below. Results of surveys along elevation gradients showed Phytophthora and vascular plant species exhibited a linearly monotonic decline with increasing elevation on roads, but not in native vegetation. However, the elevation range of Phytophthora species was higher than vascular plants on both roads and in native vegetation. Phytophthora species did not show any habitat preference and exhibited similar composition and frequency on roads and in native vegetation; vascular plants showed the opposite trend with greater frequency in native vegetation. This suggests that Phytophthora richness at the plot level mimics that of vascular plants. A changing climate may permit invasion by other Phytophthora species not yet present.
10
McCarren, Kathryn. "Saprophytic ability and the contribution of chlamydospores and oospores to the survival of Phytophthora cinnamomi." Thesis, McCarren, Kathryn (2006) Saprophytic ability and the contribution of chlamydospores and oospores to the survival of Phytophthora cinnamomi. PhD thesis, Murdoch University, 2006. https://researchrepository.murdoch.edu.au/id/eprint/190/.
Full textAbstract:
Phytophthora cinnamomi has been recognised as a key threatening process to Australia's biodiversity by the Commonwealth's Environment Protection and Biodiversity Conservation Act 1999. Despite over 80 years of extensive research, its exact mode of survival is still poorly understood. It is widely accepted that thin- and thick-walled chlamydospores are the main survival propagules while oospores are assumed to play no role in the survival of the pathogen in the Australian environment, yet evidence is limited. The saprophytic ability of the pathogen is still unresolved despite the important role this could play in the ability of the pathogen to survive in the absence of susceptible hosts. This thesis aimed to investigate chlamydospores, oospores and the saprophytic ability of P. cinnamomi to determine their contribution to survival.
Phytophthora cinnamomi did not show saprophytic ability in non-sterile soils. The production of thick-walled chlamydospores and selfed oospores of P. cinnamomi in vitro was documented. Thick-walled chlamydospores were sporadically formed under sterile and non-sterile conditions in vitro but exact conditions for stimulating their formation could not be determined. The formation of thick-walled chlamydospores emerging from mycelium of similar wall thickness was observed, challenging the current knowledge of chlamydospore formation.
Selfed oospores were abundant in vitro on modified Ribeiro's minimal medium in one isolate. Three other isolates tested also produced oospores but not in large numbers. Although the selfed oospores did not germinate on a range of media, at least 16 % were found to be viable using Thiozolyl Blue Tetrazolium Bromide staining and staining of the nuclei with 4', 6-diamidino-2-phenylindole.2HCl (DAPI). This indicated the potential of selfed oospores as survival structures and their ability to exist dormantly.
The ability of phosphite to kill chlamydospores and selfed oospores was studied in vitro. Results challenged the efficacy of this chemical and revealed the necessity for further study of its effect on survival propagules of P. cinnamomi in the natural environment. Phosphite was shown to induce dormancy in thin-walled chlamydospores if present during their formation in vitro. Interestingly, dormancy was only induced by phosphite in isolates previously reported as sensitive to phosphite and not those reported as tolerant.
Chlamydospores were produced uniformly across the radius of the colony on control modified Ribeiro's minimal medium but on medium containing phosphite (40 or 100 mcg ml-1), chlamydospore production was initially inhibited before being stimulated during the log phase of growth. This corresponded to a point in the colony morphology where mycelial density changed from tightly packed mycelium to sparse on medium containing phosphite. This change in morphology did not occur when the pathogen was grown on liquid media refreshed every four days, and chlamydospores were evenly distributed across the radius of these colonies. This trend was not observed in selfed oospores produced in the presence of phosphite. Selfed oospore production was found to be inhibited by phosphite at the same concentrations that stimulated chlamydospore production.
Isolates of P. cinnamomi were transformed using a protoplast/ polyethylene glycol method to contain the Green Fluorescent Protein and geneticin resistance genes to aid in future studies on survival properties of the organism. Although time constraints meant the stability of the transgene could not be determined, it was effective in differentiating propagules of the transformed P. cinnamomi from spores of other microrganisms in a non-sterile environment. Two different sized chlamydospores (approximately 30 mcg diameter and < 20 mcg diameter) were observed in preliminary trials of transformed P. cinnamomi inoculated lupin roots floated in non-sterile soil extracts and these were easily distinguished from microbial propagules of other species. The growth and pathogenicity was reduced in two putative transformants and their ability to fluoresce declined over ten subcultures but they still remained resistant to geneticin.
This study has improved our knowledge on the survival abilities of P. cinnamomi in vitro and has provided a useful tool for studying these abilities under more natural glasshouse conditions. Important implications of phosphite as a control have been raised.
11
McCarren, Kathryn. "Saprophytic ability and the contribution of chlamydospores and oospores to the survival of Phytophthora cinnamomi." McCarren, Kathryn (2006) Saprophytic ability and the contribution of chlamydospores and oospores to the survival of Phytophthora cinnamomi. PhD thesis, Murdoch University, 2006. http://researchrepository.murdoch.edu.au/190/.
Full textAbstract:
Phytophthora cinnamomi has been recognised as a key threatening process to Australia's biodiversity by the Commonwealth's Environment Protection and Biodiversity Conservation Act 1999. Despite over 80 years of extensive research, its exact mode of survival is still poorly understood. It is widely accepted that thin- and thick-walled chlamydospores are the main survival propagules while oospores are assumed to play no role in the survival of the pathogen in the Australian environment, yet evidence is limited. The saprophytic ability of the pathogen is still unresolved despite the important role this could play in the ability of the pathogen to survive in the absence of susceptible hosts. This thesis aimed to investigate chlamydospores, oospores and the saprophytic ability of P. cinnamomi to determine their contribution to survival.
Phytophthora cinnamomi did not show saprophytic ability in non-sterile soils. The production of thick-walled chlamydospores and selfed oospores of P. cinnamomi in vitro was documented. Thick-walled chlamydospores were sporadically formed under sterile and non-sterile conditions in vitro but exact conditions for stimulating their formation could not be determined. The formation of thick-walled chlamydospores emerging from mycelium of similar wall thickness was observed, challenging the current knowledge of chlamydospore formation.
Selfed oospores were abundant in vitro on modified Ribeiro's minimal medium in one isolate. Three other isolates tested also produced oospores but not in large numbers. Although the selfed oospores did not germinate on a range of media, at least 16 % were found to be viable using Thiozolyl Blue Tetrazolium Bromide staining and staining of the nuclei with 4', 6-diamidino-2-phenylindole.2HCl (DAPI). This indicated the potential of selfed oospores as survival structures and their ability to exist dormantly.
The ability of phosphite to kill chlamydospores and selfed oospores was studied in vitro. Results challenged the efficacy of this chemical and revealed the necessity for further study of its effect on survival propagules of P. cinnamomi in the natural environment. Phosphite was shown to induce dormancy in thin-walled chlamydospores if present during their formation in vitro. Interestingly, dormancy was only induced by phosphite in isolates previously reported as sensitive to phosphite and not those reported as tolerant.
Chlamydospores were produced uniformly across the radius of the colony on control modified Ribeiro's minimal medium but on medium containing phosphite (40 or 100 mcg ml-1), chlamydospore production was initially inhibited before being stimulated during the log phase of growth. This corresponded to a point in the colony morphology where mycelial density changed from tightly packed mycelium to sparse on medium containing phosphite. This change in morphology did not occur when the pathogen was grown on liquid media refreshed every four days, and chlamydospores were evenly distributed across the radius of these colonies. This trend was not observed in selfed oospores produced in the presence of phosphite. Selfed oospore production was found to be inhibited by phosphite at the same concentrations that stimulated chlamydospore production.
Isolates of P. cinnamomi were transformed using a protoplast/ polyethylene glycol method to contain the Green Fluorescent Protein and geneticin resistance genes to aid in future studies on survival properties of the organism. Although time constraints meant the stability of the transgene could not be determined, it was effective in differentiating propagules of the transformed P. cinnamomi from spores of other microrganisms in a non-sterile environment. Two different sized chlamydospores (approximately 30 mcg diameter and < 20 mcg diameter) were observed in preliminary trials of transformed P. cinnamomi inoculated lupin roots floated in non-sterile soil extracts and these were easily distinguished from microbial propagules of other species. The growth and pathogenicity was reduced in two putative transformants and their ability to fluoresce declined over ten subcultures but they still remained resistant to geneticin.
This study has improved our knowledge on the survival abilities of P. cinnamomi in vitro and has provided a useful tool for studying these abilities under more natural glasshouse conditions. Important implications of phosphite as a control have been raised.
12
Valer-Saldaña, Karina. "Avirulence protein Avr1b from Phytophthora sojae." [S.l.] : [s.n.], 2006. http://edoc.ub.uni-muenchen.de/archive/00006087.
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13
Valer-Saldaña, Karina. "Avirulence protein Avr1b from Phytophthora sojae." Diss., lmu, 2006. http://nbn-resolving.de/urn:nbn:de:bvb:19-60872.
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14
Olsson, Christer H. B. "Diagnosis of root-infecting Phytophthora spp. /." Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 1999. http://epsilon.slu.se/avh/1999/91-576-5483-2.pdf.
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15
Kemmitt, Gregory Miles. "Regulation of mating in Phytophthora infestans." Thesis, Bangor University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357186.
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16
Stanworth, Marie Helen. "Plasma membrane ATPase of Phytophthora cactorum." Thesis, University of the West of England, Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284886.
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17
Romanski, Annette. "Das Elicitorprotein NPP1 Isolierung und Charakterisierung der korrespondierenden cDNA, heterologe Expression des Proteins und Studien zur Signalperzeption /." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=963984098.
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18
au, M. King@murdoch edu, and Michaela King. "The phosphite responsive transcriptome of phytophthora cinnamomi." Murdoch University, 2007. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20080526.104656.
Full textAbstract:
Phosphite has been used to effectively control the soil borne plant pathogen Phytophthora cinnamomi in many horticultural crops, forest trees and natural ecosystems. However, the molecular mechanisms behind phosphite action on this pathogen are poorly understood.
Several studies have shown that phosphite inhibits growth and zoospore production of P. cinnamomi and in addition induces significant physiological and metabolic changes in the mycelium. As an approach to understanding the mechanisms and relevance of these changes in the pathogen, the effect of phosphite on gene expression was investigated using microarray analysis. To construct the microarray, RNA was extracted from phosphite-treated (40 ug/ml) mycelium of P. cinnamomi isolate MP 80. The chosen phosphite concentration inhibited the mycelial growth by 70% but provided sufficient mycelium for RNA extractions after 4 days growth at 25C.
The mRNA was reverse transcribed into cDNA and cloned into lambda to construct a library consisting of 2 million pfu of which 80 % were recombinant phage. The inserts were sequenced for a random selection of clones from the library. The nucleotide sequences generated revealed a range of different P. cinnamomi genes being expressed and demonstrated that the cDNA library provided a good representation of the transcripts expressed in P. cinnamomi. The types of genes found to be expressed in the mycelium of P. cinnamomi included genes encoding GTP binding proteins involved in vesicle transport, structural proteins involved in maintaining cell membrane integrity,elicitors, phosphatases and ribosomal proteins.
Over nine thousand cDNA transcripts were randomly selected from the cDNA library and prepared by PCR amplification and purification for microarray construction. Custom made cDNA arrays containing 9216 cDNA transcripts were constructed and probed with RNA from untreated mycelium and mycelium grown in medium with 40 ug/ml phosphite.
Two genes, EF-1 alpha and cinnamomin gene, identified by qRT-PCR as being constitutively expressed were also positioned on the arrays as positive controls. In the process of identifying constitutively expressed genes, qRT PCR revealed that phosphite down-regulated a gene encoding ubiquitin-conjugating enzyme, a component of the ubiquitin/proteasome pathway involved in the removal of abnormal and short lived-regulatory proteins and rate limiting enzymes.
From the arrays a further seventy-two transcripts with altered patterns in gene expression (fold change > 2) were identified. The majority of the cDNA transcripts spotted on the array were down-regulated with changes in gene expression ranging from 2- to 3.5-fold. Thirty-two cDNA transcripts were up-regulated with changes in gene expression ranging from 2- to 16-fold. Characterisation by sequencing revealed that the most highly induced transcripts coded for ADP-ribosylation factors, an ABC cassette transporter and a glycosyl transferase. A transcript encoding a vitamin B6 biosynthesis protein was also identified as up-regulated by 2.9-fold. In contrast, the down-regulated transcripts coded for cellulose synthase I, annexin, glutamine synthetase, metallothionein and an alternative oxidase. The results are discussed in terms of possible roles and mechanism(s) of phosphite action within the mycelium of P.cinnamomi.
This work is the first comprehensive screen for phosphite regulated-gene expression in P. cinnamomi and represents a significant step towards an understanding of the mode of action of phosphite on this organism. This thesis provides valuable information on the molecular interaction between phosphite and P. cinnamomi, which in future studies may stimulate the discovery of novel methods and cellular targets for the control of plant pathogenic Oomycetes.
19
Andersson, Björn. "Sexual reproduction in Phytophthora infestans : epidemiological consequences /." Uppsala : Dept. of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, 2007. http://epsilon.slu.se/200777.pdf.
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20
Walker, C. "Gene silencing and development in Phytophthora infestans." Thesis, University of Aberdeen, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590982.
Full textAbstract:
In order to investigate whether epigenetics plays a role in P. infestans, the expression patterns of genes involved in transcriptional and post-transcriptional gene silencing were investigated and several were found to be up-regulated in both pre-infection stages and in planta. A histone deacetylase (Pi-HDA1) was selected for functional characterization using RNA interference (RNAi). Silencing Pi-HDA1 produced large aberrant zoospores indicating that it may be required for development. In addition silencing of Pi-HDA1 resulted in reactivation of INF1 production in inf1-transgenic silenced strains, therefore suggesting that Pi-HDA1 may be directly involved in the silencing of inf1 in inf1-transgenic silenced strains. In addition an RNA helicase, Pi-RNH1 was also found to be specifically up-regulated in zoospores. Pi-RNH1-silenced strains produced large aberrant zoospores that had undergone partial cleavage and often had multiple flagella on their surface. The Pi-RNH1-silenced zoospores were also sensitive to osmotic pressure and they often ruptured upon release from the sporangia. These findings indicate that Pi-RNH1 has a major function in zoospore development. In addition the mechanism of internuclear gene silencing was further investigated. In P. infestans internuclear gene silencing is a process where silencing is transmitted from nucleus to nucleus in heterokaryotic strains. Previously it was demonstrated that internuclear gene silencing is a transcriptional silencing process. In several eukaryotes transcriptional silencing has been shown to involve methylation of cytosines. Methylation sensitive sequencing was performed and it was concluded that DNA methylation is not involved in transcriptional silencing in P. infestans. In solution hybridization assays provided preliminary evidence that small RNAs may be the diffusible factor responsible for the spread of silencing.
21
El-Gariani, Najat Khalifa. "Nutrient uptake by Peronospora and Phytophthora hyphae." Thesis, University of the West of England, Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275354.
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22
Middleton, J. "Potentially pathogenic Phytophthora isolates in irrigation systems." Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354090.
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23
Berg, Isak. "Analysis of α-actinin in Phytophthora infestans." Thesis, Umeå universitet, Kemiska institutionen, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-150537.
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24
Hulbert, Joey Michael. "Phytophthora diversity in the Cape Floristic Region." Thesis, University of Pretoria, 2020. http://hdl.handle.net/2263/77828.
Full textAbstract:
The biodiversity in the Cape Floristic Region of South Africa faces many threats
from anthropogenic sources such as the trade associated with our globalized economy.
Aggressive plant pathogens in the genus Phytophthora are of particular concern because
of their capacity to invade and change plant communities and their frequent
dissemination via global trade. The fact that South Africa has a developing economy with
many socioeconomic challenges, the capacity to monitor the abundance of plants
imported for pests and pathogens is largely inadequate. Consequently, low cost methods
to enhance post-border surveillance for the emergence of Phytophthora species are
critically needed in South Africa. Therefore, the major aims of the research conducted in
this thesis were to: 1) reveal the diversity and potential threats of Phytophthora species
already present within the Cape Floristic Region, and 2) provide information and an
example of an approach to enhance the biosecurity with public engagement in South
Africa. Through independent sampling and a newly developed citizen science program,
this body of work revealed the presence of seventeen described Phytophthora species,
one informally described Phytophthora species, and three putative hybrids. Seven of
these Phytophthora species were not previously known to occur in South Africa. The
work also revealed a relationship between the invasion of P. cinnamomi and the health of
trees and evidence is provided for dissimilarity between invaded and non-invaded plant
communities. In addition, through a synthesis of modern Phytophthora species
descriptions and a diversity study in botanical gardens, it was possible to provide
evidence for the importance of surveying urban environments. Then as a means to
demonstrate the potential of public engagement to enhance biosecurity, the findings from
activities in Cape Citizen Science have been summarized. In this case it was possible to
show that nine of the Phytophthora species were recovered only because of citizen
participation. Cumulatively, this thesis has advanced the base of knowledge regarding the
presence and consequences of Phytophthora species in the Cape Floristic Region. In this
sense, they also provide valuable information and a model system to enhance biosecurity
in South Africa as well as in countries with similar economies.Thesis (PhD)--University of Pretoria, 2020.
Microbiology and Plant Pathology
PhD
Unrestricted
25
Reitmann, Anandi. "Identification of pathogenicity genes in Phytophthora cinnamomi." Diss., University of Pretoria, 2014. http://hdl.handle.net/2263/79179.
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26
Vauthrin, Sébastien. "L'interaction tabac / Phytophthora : dissection d'un modèle complexe." Dijon, 2000. http://www.theses.fr/2000DIJOS035.
Full textAbstract:
Les élicitines, protéines sécrétées par les champignons du genre phytophthora, élicitent les mécanismes de défense du tabac, Nicotiana tabacum var. Xanthi, sur plante entière et sur suspension cellulaire. Ces protéines présentent également une activité de protéines de transfert de stérol. Au cours de ce travail, nous avons démontré que les élicitines sont capables de transférer des stérols entre des liposomes, des micelles et également entre des membranes biologiques. La mutagenèse dirigée du gène x24 codant la cryptogéine, afin de remplacer les résidus tyrosines intervenant dans la liaison du stérol a l'élicitine, nous a permis d'obtenir des élicitines aux capacités plus ou moins réduites à interagir avec des stérols. Nous avons ainsi pu démontrer l'existence d'une relation entre cette fonction et la capacité de fixation des élicitines sur leur site de fixation spécifique situé sur la membrane plasmique des cellules de tabac. C'est en fait un complexe élicitine-stérol qui se fixe sur ces sites et non une élicitine non chargée. Nous avons ensuite démontré l'existence d'une relation entre la capacité de fixation des élicitines sur leurs sites à haute affinité et la capacité de ces protéines à induire les mécanismes de défense sur suspension cellulaire de tabac. Nous avons ainsi relié l'induction des mécanismes de défense et la fixation des élicitines sur ce qui semble donc être leur récepteur membranaire capable de transmettre un signal du milieu extracellulaire vers le milieu intracellulaire. Nous avons par la suite étudié la capacité des élicitines à interagir avec d'autres lipides. Nous avons montré que les élicitines interagissent avec des acides gras et des phospholipides, transférant ces derniers entre des liposomes. Les élicitines semblent ainsi former une famille de protéines de transfert de lipides. Tout comme pour les stérols, ces autres lipides pourraient jouer un rôle dans la reconnaissance de l'élicitine par son récepteur. Enfin, le clonage, par la méthode du double hybride, de l’ADNc codant ce récepteur a permis de mettre en évidence la présence de plusieurs protéines affines pour la cryptogéine. Toutes ces protéines sont de nature intracellulaire, laissant envisage une éventuelle internalisation de l'élicitine dans les cellules végétales.
27
Huitema, Edgar. "Determinants of nonhost resistance to phytophthora infestans." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1117038573.
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28
King, Michaela. "The phosphite responsive transcriptome of phytophthora cinnamomi." Thesis, King, Michaela (2007) The phosphite responsive transcriptome of phytophthora cinnamomi. PhD thesis, Murdoch University, 2007. https://researchrepository.murdoch.edu.au/id/eprint/132/.
Full textAbstract:
Phosphite has been used to effectively control the soil borne plant pathogen Phytophthora cinnamomi in many horticultural crops, forest trees and natural ecosystems. However, the molecular mechanisms behind phosphite action on this pathogen are poorly understood.
Several studies have shown that phosphite inhibits growth and zoospore production of P. cinnamomi and in addition induces significant physiological and metabolic changes in the mycelium. As an approach to understanding the mechanisms and relevance of these changes in the pathogen, the effect of phosphite on gene expression was investigated using microarray analysis. To construct the microarray, RNA was extracted from phosphite-treated (40 ug/ml) mycelium of P. cinnamomi isolate MP 80. The chosen phosphite concentration inhibited the mycelial growth by 70% but provided sufficient mycelium for RNA extractions after 4 days growth at 25C.
The mRNA was reverse transcribed into cDNA and cloned into lambda to construct a library consisting of 2 million pfu of which 80 % were recombinant phage. The inserts were sequenced for a random selection of clones from the library. The nucleotide sequences generated revealed a range of different P. cinnamomi genes being expressed and demonstrated that the cDNA library provided a good representation of the transcripts expressed in P. cinnamomi. The types of genes found to be expressed in the mycelium of P. cinnamomi included genes encoding GTP binding proteins involved in vesicle transport, structural proteins involved in maintaining cell membrane integrity,elicitors, phosphatases and ribosomal proteins.
Over nine thousand cDNA transcripts were randomly selected from the cDNA library and prepared by PCR amplification and purification for microarray construction. Custom made cDNA arrays containing 9216 cDNA transcripts were constructed and probed with RNA from untreated mycelium and mycelium grown in medium with 40 ug/ml phosphite.
Two genes, EF-1 alpha and cinnamomin gene, identified by qRT-PCR as being constitutively expressed were also positioned on the arrays as positive controls. In the process of identifying constitutively expressed genes, qRT PCR revealed that phosphite down-regulated a gene encoding ubiquitin-conjugating enzyme, a component of the ubiquitin/proteasome pathway involved in the removal of abnormal and short lived-regulatory proteins and rate limiting enzymes.
From the arrays a further seventy-two transcripts with altered patterns in gene expression (fold change > 2) were identified. The majority of the cDNA transcripts spotted on the array were down-regulated with changes in gene expression ranging from 2- to 3.5-fold. Thirty-two cDNA transcripts were up-regulated with changes in gene expression ranging from 2- to 16-fold. Characterisation by sequencing revealed that the most highly induced transcripts coded for ADP-ribosylation factors, an ABC cassette transporter and a glycosyl transferase. A transcript encoding a vitamin B6 biosynthesis protein was also identified as up-regulated by 2.9-fold. In contrast, the down-regulated transcripts coded for cellulose synthase I, annexin, glutamine synthetase, metallothionein and an alternative oxidase. The results are discussed in terms of possible roles and mechanism(s) of phosphite action within the mycelium of P.cinnamomi.
This work is the first comprehensive screen for phosphite regulated-gene expression in P. cinnamomi and represents a significant step towards an understanding of the mode of action of phosphite on this organism. This thesis provides valuable information on the molecular interaction between phosphite and P. cinnamomi, which in future studies may stimulate the discovery of novel methods and cellular targets for the control of plant pathogenic Oomycetes.
29
King, Michaela. "The phosphite responsive transcriptome of Phytophthora cinnamomi /." King, Michaela (2007) The phosphite responsive transcriptome of phytophthora cinnamomi. PhD thesis, Murdoch University, 2007. http://researchrepository.murdoch.edu.au/132/.
Full textAbstract:
Phosphite has been used to effectively control the soil borne plant pathogen Phytophthora cinnamomi in many horticultural crops, forest trees and natural ecosystems. However, the molecular mechanisms behind phosphite action on this pathogen are poorly understood.
Several studies have shown that phosphite inhibits growth and zoospore production of P. cinnamomi and in addition induces significant physiological and metabolic changes in the mycelium. As an approach to understanding the mechanisms and relevance of these changes in the pathogen, the effect of phosphite on gene expression was investigated using microarray analysis. To construct the microarray, RNA was extracted from phosphite-treated (40 ug/ml) mycelium of P. cinnamomi isolate MP 80. The chosen phosphite concentration inhibited the mycelial growth by 70% but provided sufficient mycelium for RNA extractions after 4 days growth at 25C.
The mRNA was reverse transcribed into cDNA and cloned into lambda to construct a library consisting of 2 million pfu of which 80 % were recombinant phage. The inserts were sequenced for a random selection of clones from the library. The nucleotide sequences generated revealed a range of different P. cinnamomi genes being expressed and demonstrated that the cDNA library provided a good representation of the transcripts expressed in P. cinnamomi. The types of genes found to be expressed in the mycelium of P. cinnamomi included genes encoding GTP binding proteins involved in vesicle transport, structural proteins involved in maintaining cell membrane integrity,elicitors, phosphatases and ribosomal proteins.
Over nine thousand cDNA transcripts were randomly selected from the cDNA library and prepared by PCR amplification and purification for microarray construction. Custom made cDNA arrays containing 9216 cDNA transcripts were constructed and probed with RNA from untreated mycelium and mycelium grown in medium with 40 ug/ml phosphite.
Two genes, EF-1 alpha and cinnamomin gene, identified by qRT-PCR as being constitutively expressed were also positioned on the arrays as positive controls. In the process of identifying constitutively expressed genes, qRT PCR revealed that phosphite down-regulated a gene encoding ubiquitin-conjugating enzyme, a component of the ubiquitin/proteasome pathway involved in the removal of abnormal and short lived-regulatory proteins and rate limiting enzymes.
From the arrays a further seventy-two transcripts with altered patterns in gene expression (fold change > 2) were identified. The majority of the cDNA transcripts spotted on the array were down-regulated with changes in gene expression ranging from 2- to 3.5-fold. Thirty-two cDNA transcripts were up-regulated with changes in gene expression ranging from 2- to 16-fold. Characterisation by sequencing revealed that the most highly induced transcripts coded for ADP-ribosylation factors, an ABC cassette transporter and a glycosyl transferase. A transcript encoding a vitamin B6 biosynthesis protein was also identified as up-regulated by 2.9-fold. In contrast, the down-regulated transcripts coded for cellulose synthase I, annexin, glutamine synthetase, metallothionein and an alternative oxidase. The results are discussed in terms of possible roles and mechanism(s) of phosphite action within the mycelium of P.cinnamomi.
This work is the first comprehensive screen for phosphite regulated-gene expression in P. cinnamomi and represents a significant step towards an understanding of the mode of action of phosphite on this organism. This thesis provides valuable information on the molecular interaction between phosphite and P. cinnamomi, which in future studies may stimulate the discovery of novel methods and cellular targets for the control of plant pathogenic Oomycetes.
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Gilovitz, Joshua. "Screening Lambertia for resistance to Phytophthora cinnamomi." Thesis, Gilovitz, Joshua (2007) Screening Lambertia for resistance to Phytophthora cinnamomi. Honours thesis, Murdoch University, 2007. https://researchrepository.murdoch.edu.au/id/eprint/32597/.
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Johnson, Regina. "Stream baiting for sudden oak death : fluvial transport and ecohydrology of the invasive plant pathogen Phytophthora ramorum in Western Washington State /." Online pdf file accessible through the World Wide Web, 2008. http://archives.evergreen.edu/masterstheses/Accession86-10MES/2008Johnson_RMMESthesis.pdf.
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Boava, Leonardo Pires [UNESP]. "Estabilidade de QTLs ligados à resistência dos citros a gomose, causada por Phytophthora parasitica." Universidade Estadual Paulista (UNESP), 2004. http://hdl.handle.net/11449/97219.
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Phytophthora parasitica, principal causador da gomose dos citros, é um importante patógeno dos citros provocando danos em viveiros e no campo. Programas de melhoramento visando obtenção de plantas resistentes a P. parasitica exigem informações detalhadas sobre o tipo de herança e a localização de genes de resistência no genoma. Fontes de resistência às doenças podem ser encontradas em gêneros correlatos a citros como Poncirus sp. O presente estudo teve como objetivos detectar e verificar a estabilidade de marcadores moleculares e locos controladores de características quantitativas (QTLs) ligados à resistência a gomose em uma progênie F1 obtida do cruzamento entre Citrus sunki vs. Poncirus trifoliata 'Rubidoux'. As avaliações fenotípicas de três conjuntos de dados de 3 épocas de avaliação distintas foram incorporadas às informações dos mapas de ligação estabelecidos através de marcadores moleculares do tipo RAPD. Plantas jovens foram inoculadas com o patógeno, usando o método do disco e avaliadas medindo-se o comprimento da lesão. A estratégia do 'pseudo-testcross' foi adotada como delineamento genético. Os QTLs foram mapeados utilizando o método do mapeamento por intervalo composto (CIM) com o programa QTLCartographer v.1.25. A partir das média de todos os experimentos, foram identificadas 5 posições nos grupos de ligação II, III e V de P. trifoliata associadas à gomose de Phytophthora. Em 2 posições observou-se uma correlação na detecção de QTLs para as avaliações realizadas em duas das três épocas. Demonstrado desta forma a ocorrência da interação genótipo ambiente.
P. parasitica, is the most important main causal agent of Citrus Phytophthora gummosis in Brazil and hve caused damage in nurseries and orchards. Improving resistence programs to get resistant to P. parasitica have been detailed information about the inheritance and gene localization resistance. Source of disease resistance can be found in correlated genera like Poncirus trifoliata. The present study had the objective of detecting molecular markers associated to quantitative trait loci (QTL) for resistance to Citrus Phytophthora gummosis using F1 lineage obtained between Citrus sunki vs. Poncirus trifoliata 'Rubidoux' cross. Phenotypical evaluations will be incorporated in linkage maps established through RAPD molecular markers. Young plants were inoculated with P. parasitica, using the disc method and evaluated after one month measuring lesions length. Pseudo-testcross strategy was be used for genetic outlining. All this information were evaluated in specific genetic-statistical programs. QTLs were mapped using the method of the maps for composed interval (CIM) with the program QTLCartographer v.1.25. CIM. Starting from the average of all of the experiments, they were identified 2 positions in the group of connection II of P. trifoliata associated with gomose of Phytophthora. In each area a correlation was observed in the detection of QTLs for the evaluations accomplished in two of the three times... (Complete abstract, click electronic address below).
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Brand, Simone Cristiane. "Taxtomina A e Piriformospora indica no controle de Phytophthora nicotianae em citros e Phytophthora plurivora em faia (Fagus sylvatica)." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/11/11135/tde-10052016-132152/.
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Espécies de Phytophthora tem se destacado ao longo da história devido ao seu potencial destrutivo, se iniciando com a devastadora P. infestans na Irlanda e se estende até os dias de hoje com P. nicotianae em citros e P. plurivora em faia. Uma característica importante deste grupo de patógenos é que as medidas de controle da doença se baseiam na prevenção da entrada do patógeno na área visto que, uma vez instalado, o produtor precisa conviver com o mesmo, pois não se dispõem de métodos efetivos de controle. Neste sentido, a busca por métodos de controle torna-se primordial. O endofítico radicular Piriformospora indica, tem-se destacado em vários patossistemas devido a sua habilidade de induzir resistência contra patógenos, aumentar a tolerância à estresses abióticos e promover o crescimento de plantas. Taxtomina A, produzida por Streptomyces scabies, é capaz de ativar mecanismos de defesa de plantas, os quais são efetivos contra agentes patogênicos. Objetivou-se com este trabalho avaliar o efeito de P. indica e da taxtomina A sobre P. nicotianae em citros e P. plurivora em faia. Ambos foram avaliados quanto ao seu efeito direto sobre os patógenos em questão. O indutor de defesa vegetal Bion® foi utilizado em alguns ensaios para fins de comparação. Plântulas de citros e faia foram tratadas com concentrações crescentes de taxtomina e parâmetros fisiológicos, bioquímicos e de controle da doença foram avaliados. Taxtomina A não apresenta efeito direto sobre os patógenos avaliados. Os dados de incidência da doença em plântulas de faia tratadas com taxtomina A nas concentrações de 10, 25, 50 e 100 μg se mostraram consistentes com a quantidade de DNA do patógeno no sistema radicular, demonstrando que, aparentemente, a toxina induziu suscetibilidade nas plântulas de faia. Em citros, para os parâmetros fisiológicos e bioquímicos avaliados, em linhas gerais, a taxtomina A nas concentrações de 50 e 100 μg demonstrou potencial de aplicação no patossistema citros - P. nicotianae. Quando avaliada a mortalidade de plantas inoculadas com o patógeno e tratadas com taxtomina, bem como, quando quantificado o DNA do oomiceto no sistema radicular, as referidas concentrações também apresentaram os melhores desempenhos. Plântulas das mesmas espécies foram submetidas a inoculação com P. indica, sendo avaliados os efeitos na promoção de crescimento, na atividade de enzimas e de genes relacionados ao processo de defesa, bem como, no controle da doença. Não foi observado efeito direto do endofítico radicular sobre os patógenos avaliados. Quando plântulas de citros foram inoculadas com P. indica e depois com P. nicotianae, não foi observada promoção de crescimento e controle da doença. As análises histológicas e moleculares demonstraram a presença do endofítico no sistema radicular de plântulas de citros e faia. Análises bioquímicas revelaram apenas aumentos pontuais no teor de proteínas e na atividade da β-1,3-glucanase e da peroxidase no tratamento com P. indica + P. nicotianae. Os genes PR-1.4, PR-1.8, PR-β-glucosidase e Hsp70 foram induzidos em plântulas inoculadas com P. indica e com o patógeno, bem como no tratamento com Bion® e patógeno, porém em menor magnitude. O endofítico P. indica ativa o sistema de defesa de plântulas de citros, no entanto, os mecanismos ativados não são efetivos para o controle da doença na interação citros - P. nicotianae.Phytophthora species has been important throughout history because of its destructive potential, starting with the devastating P. infestans in potatos in Ireland and extending to the present day with Phytophthora nicotianae on citrus and Phytophthora plurivora on beech. An important feature of this group of pathogens is that the disease control measures are based upon prevention of pathogen entry into the area since, once installed, producers have to live with it, because they do not have effective methods of control. Accordingly, the search for control methods becomes essential. The root endophytic fungus Piriformospora indica has been shown to induce resistance against pathogens, increase tolerance to abiotic stresses and promote the growth of plants. On the other hand, the phytotoxin thaxtomin A, produced by Streptomyces scabies, is able to activate plant defense mechanisms, which are effective against pathogens. Thus, the objective of this study was to evaluate the effect of P. indica and thaxtomin A on the control of P. nicotianae on citrus and P. plurivora on beech. Both were assessed for their direct effect on these pathogens. The plant defense inducer Bion® was used in some tests for comparison. Besides that, seedlings of citrus or beech were treated with P. indica or increasing concentrations of thaxtomin and physiological / biochemical parameters as well as those related to induction of resistance and disease control were evaluated. The results showed that thaxtomin A did no exhibit any direct effect on the pathogens. The incidence of disease on beech seedlings treated with thaxtomin A, in concentrations of 10, 25, 50 and 100 ug, were consistent with the amount of DNA of the pathogen in the root tissue, demonstrating that, apparently, the toxin induced susceptibility in the seedlings. In citrus, for the physiological and biochemical parameters evaluated, in general, the thaxtomin in the concentrations of 50 and 100 ug showed potential for application in the citrus pathosystem - P. nicotianae. When the mortality of the seedlings treated with thaxtomin and inoculated with the pathogen as well as the oomycete DNA amount in the root system were evaluated these concentrations also had the best performances. As mentioned above, seedlings of beech or citrus were also inoculated with the endophyte and its effect on growth promotion, enzyme activities, the expression of genes related to defense process and on disease control was measured. There was no direct effect of the root endophyte on the pathogens. When citrus seedlings were inoculated with P. indica and then with P. nicotianae, there was no growth promotion or disease control. Histological and molecular analysis showed the presence of the endophytic fungus inside the root system of citrus and beech seedlings. Biochemical analyzes revealed only occasional increases in protein content and the activities of β-1,3-glucanase and peroxidase in the treatment with P. indica + P. nicotianae in citrus seedlings. The genes PR-1.4, PR- 1.8, PR-β-glucosidase and Hsp70 were induced in seedlings inoculated with P. indica and challenged with the pathogen as well as in the treatment with the resistance inducer Bion® plus pathogen, but to a lesser magnitude. Finally, the endophytic P. indica is able to active defense system in citrus, however, the activated mechanisms seems not to be effective in controlling the disease in the interaction citrus - P. nicotianae.
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Porschewski, Peter. "Klonierung und cytologisch-biochemische Charakterisierung von Chaperonen in Phytophthora megasperma." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=962374911.
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Castillo, Ruiz Rosa Angela. "A potato large insert library for isolation of candidate loci for late blight resistance and studies on their genome organization." [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=970045794.
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Li, Shuang. "Proteomic analysis of secreted proteins from Phytophthora infestans." Thesis, University of Aberdeen, 2004. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=165891.
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In order to identify potential avirulence factors of Phytophthora infestans, secreted protein profiles of six strains (IPO-0, CBS431.90, IPO-655-2A, IPO-428-2, 88069 and 90128) with different avirulence phenotypes were analysed by proteomics. The proteins from culture filtrates were visualised on 2D gels with a total number between 350 and 1000. PiAVR X was found only in avirulent strains and considered therefore as a possible avirulence determinant. Its expression increased in all strains tested when grown in Modified Henniger medium. Single nucleotide polymorphisms (SNPs) were detected within a 735 nt fragment of PiAvrX but none was linked to avirulence characteristics. The consensus EST database facilitated identification of approximately 50% of 45 most abundant proteins excised from strain 88069. Beta-glucosidase, Pi-NIP2 (Phytophthora infestans necrosis inducing protein-like protein), enoyl CoA hydratase, glutathione S transferase, peptidylprolyl isomerase, acidic chitinase and Pi-PR1 (Phytophthora infestans homologue of plant PR-1 protein) were among the identified proteins with a recognisable signal sequence. Enolase, quinine-oxido reductase, nucleoside di-phosphate kinase, actin depolymerisation factor, thioredoxin, ubiquitin and 14-3-3 protein were also identified but without a signal peptide. The occurrence and expression of Pi-nip2, Pi-chi1 and Pi-pr1 were confirmed in the strains tested. Transformants were obtained from P. infestans strain T30-4 via a biolistic particle delivery approach using a single plasmid vector containing Pi-pr1. Detailed analysis of these transformants did not demonstrate induction of homology-dependent gene silencing. It was found that transformation rates were different among the tested P. infestans strains.
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FLAMENT, MARIE-HENRIETTE. "Cartographie genetique de facteurs impliques dans la resistance du cacaoyer (theobroma cacao l. ) a phytophthora megakarya et a phytophthora palmivora." Montpellier, ENSA, 1998. http://www.theses.fr/1998ENSA0030.
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Phytophthora palmivora et p. Megakarya sont deux especes de champignon responsables de la pourriture brune des fruits du cacaoyer pouvant occasionner respectivement jusqu'a 30 et 50% de pertes. P. Palmivora est une espece plus repandue que p. Megakarya. Jusqu'a present, aucun cacaoyer totalement resistant a ces phytophthorae n'a ete identifie. Les seules resistances connues sont des resistances partielles. Afin de connaitre le determinisme genetique de resistance, quatre descendances au cameroun ont ete etudiees en condition naturelle d'infection au champ et en condition artificielle d'infection sur feuille et sur fruit par p. Megakarya. Une descendance en cote d'ivoire a ete evaluee pour la resistance a p. Palmivora avec les memes caracteres de resistance. Les cartes genetiques de ces descendances ont ete realisees a l'aide de marqueurs moleculaires : rflp, ssr et aflp. Cinq qtls de resistance a p. Megakarya et cinq autres qtls de resistance a p. Palmivora ont ete detectes pour l'ensemble des caracteres mesures par les trois methodes d'evaluation de la resistance. Des genes differents semblent impliques dans les differents caracteres mesures par chacune des methodes d'evaluation de la resistance, suggerant l'implication de divers mecanismes de resistance et confirmant l'absence de correlation observee entre ces methodes. Ces methodes apparaissent sensibles aux conditions environnementales. L'amelioration des mesures de la resistance est discutee ainsi que l'interpretation des qtls detectes. Une region genomique sur le chromosome 9 cumule des qtls de resistance communs aux deux especes fongiques pour un meme caractere de resistance et pourrait etre particulierement interessante pour la selection assistee par marqueurs.
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Fitzpatrick-Peabody, Erica. "Methodology and Assessment of the Susceptibility of Potato Genotypes to Phytophthora Erythrosetpica Causal Organism of Pink Rot." Fogler Library, University of Maine, 2008. http://www.library.umaine.edu/theses/pdf/Fitzpatrick-PeabodyER2008.pdf.
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Boava, Leonardo Pires. "Estabilidade de QTLs ligados à resistência dos citros a gomose, causada por Phytophthora parasitica /." Botucatu : [s.n.], 2004. http://hdl.handle.net/11449/97219.
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Orientador: Edson Luiz FurtadoBanca: Nilton Luiz de Souza
Banca: Marcos Antonio Machado
Resumo: Phytophthora parasitica, principal causador da gomose dos citros, é um importante patógeno dos citros provocando danos em viveiros e no campo. Programas de melhoramento visando obtenção de plantas resistentes a P. parasitica exigem informações detalhadas sobre o tipo de herança e a localização de genes de resistência no genoma. Fontes de resistência às doenças podem ser encontradas em gêneros correlatos a citros como Poncirus sp. O presente estudo teve como objetivos detectar e verificar a estabilidade de marcadores moleculares e locos controladores de características quantitativas (QTLs) ligados à resistência a gomose em uma progênie F1 obtida do cruzamento entre Citrus sunki vs. Poncirus trifoliata 'Rubidoux'. As avaliações fenotípicas de três conjuntos de dados de 3 épocas de avaliação distintas foram incorporadas às informações dos mapas de ligação estabelecidos através de marcadores moleculares do tipo RAPD. Plantas jovens foram inoculadas com o patógeno, usando o método do disco e avaliadas medindo-se o comprimento da lesão. A estratégia do 'pseudo-testcross' foi adotada como delineamento genético. Os QTLs foram mapeados utilizando o método do mapeamento por intervalo composto (CIM) com o programa QTLCartographer v.1.25. A partir das média de todos os experimentos, foram identificadas 5 posições nos grupos de ligação II, III e V de P. trifoliata associadas à gomose de Phytophthora. Em 2 posições observou-se uma correlação na detecção de QTLs para as avaliações realizadas em duas das três épocas. Demonstrado desta forma a ocorrência da interação genótipo ambiente.
Abstract: P. parasitica, is the most important main causal agent of Citrus Phytophthora gummosis in Brazil and hve caused damage in nurseries and orchards. Improving resistence programs to get resistant to P. parasitica have been detailed information about the inheritance and gene localization resistance. Source of disease resistance can be found in correlated genera like Poncirus trifoliata. The present study had the objective of detecting molecular markers associated to quantitative trait loci (QTL) for resistance to Citrus Phytophthora gummosis using F1 lineage obtained between Citrus sunki vs. Poncirus trifoliata 'Rubidoux' cross. Phenotypical evaluations will be incorporated in linkage maps established through RAPD molecular markers. Young plants were inoculated with P. parasitica, using the disc method and evaluated after one month measuring lesions length. Pseudo-testcross strategy was be used for genetic outlining. All this information were evaluated in specific genetic-statistical programs. QTLs were mapped using the method of the maps for composed interval (CIM) with the program QTLCartographer v.1.25. CIM. Starting from the average of all of the experiments, they were identified 2 positions in the group of connection II of P. trifoliata associated with gomose of Phytophthora. In each area a correlation was observed in the detection of QTLs for the evaluations accomplished in two of the three times... (Complete abstract, click electronic address below).
Mestre
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Carter, Deidre Anne. "DNA polymorphisms as genetic markers in Phytophthora infestans." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46699.
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Clayton, Robert Charles. "Integrated control of potato late-blight (Phytophthora infestans)." Thesis, Bangor University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357249.
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Shepherd, Samantha J. "Analysis of Phytophthora palmivora zoosporogenesis and zoospore chemotaxis." Thesis, University of Aberdeen, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327418.
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Thompson, J. M. "Phytophthora Infestans in Potato Tubers : Infection and Transmission." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501594.
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Araujo, Maria Nilsa Martins de. "Análise de sobrevivência do tomateiro a Phytophthora infestans." Universidade Federal de Viçosa, 2008. http://locus.ufv.br/handle/123456789/4014.
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Reburning caused by Phytophthora infestansis is characterized as an aggressive disease of great destructive impact, capable of limiting or even hindering the economic cultivation of the tomato plant under conditions of high humidity and low temperatures. In view of the problems reburning can cause to tomato plant crops, this work aimed to: 1) fit models to describe the progress of the disease and form groups of tomato accesses with similar curves; 2) estimate data referring to the number of days to reach 5% severity of the disease, by means of inverse regression; 3) fit survival curves by means of the Kaplan-Meier estimator for the access groups and compare them by means of the Logrank test;4)fit survival curves by means of probabilistic models and compare these curves with Kaplan Meir´s non-parametric technique. Using tomato reburning real data, it was possible to fit the exponential model (Y = y0 exp (rX)) to describe the disease s progress. The means of the parameter estimates were submitted to grouping analysis using the centroid method, generating 10 access groups. Time up to 5% of the disease was calculated via inverse regression. Non-parametric techniques were used to estimate survival function by means of the Kaplan-Meier´s estimator to compare the survival curves by the Logrank test .The survival function was also fit using the probabilistic models, exponential Weibull and Log-normal, respectively, which were compared by means of the verisimilitude ratio test (VRT), considering the generalized Gamma model, as a general case for these models. The methodology applied allowed fitting the exponential model to describe tomato plant reburning progress and to regroup the accesses studied in the 10 groups. The access BGH-6 obtained a smaller disease progress than the others, thus characterizing its higher resistance to the disease; An inverse regression allowed time estimation up to the occurrence of 5% of the severity of the tomato plant reburning. The Kaplan-Meier ´s non-parametric technique allowed estimating the survival curves of the tomato plant accesses belonging to the groups 1, 2, 4, 6 and 8. Utilizing the Logrank test, it could be concluded that most two-by-two comparisons were significant (p<0.05), except in the comparisons of groups 2x4, 4x8 and 6x8. The use of the probabilistic models, exponential Weibull and Log-normal allowed estimating the survival curves of groups 2, 4, 6 and 8, except for group 4, to which the Weibull model was not adequate. Comparing the probabilistic models with the non-parametric technique, the curves of the probabilistic models of groups 2 and 4 presented satisfactory results, compared to the curve estimated by Kaplan-Meier.
A requeima causada por Phytophthora infestans caracteriza-se por ser uma doença agressiva e de grande impacto destrutivo, podendo limitar ou até mesmo impedir o cultivo econômico do tomateiro sob condições de alta umidade e baixas temperaturas. Diante dos problemas que a requeima pode provocar às lavouras de tomate, este trabalho teve por objetivos: 1) ajustar modelos para descrever o progresso da doença e formar grupos de acessos de tomateiro com curvas semelhantes; 2) estimar dados referentes ao número de dias até atingir 5% de severidade da doença, por meio de regressão inversa; 3) ajustar curvas de sobrevivência por meio do estimador de Kaplan-Meier para grupos de acessos e compará-las mediante o uso do teste Logrank; 4) ajustar curvas de sobrevivência por meio de modelos probabilísticos e compará-las com a técnica não-paramétrica de Kaplan-Meier. Utilizando dados reais sobre a requeima do tomateiro, foi possível ajustar o modelo exponencial (Y = y0 exp (rX)) para descrever o progresso da doença. As médias das estimativas dos parâmetros foram submetidas à análise de agrupamento pelo método Centróide, o que gerou 10 grupos de acessos, sendo o tempo até a incidência de 5% da doença calculado via regressão inversa. Foram utilizadas técnicas não-paramétricas para estimar a função de sobrevivência por meio do estimador de Kaplan-Meier e para comparar as curvas de sobrevivência pelo teste Logrank. Foi também ajustada a função de sobrevivência, empregando-se os modelos probabilísticos Exponencial, Weibull e Log-normal, os quais foram comparados por meio do Teste da Razão da Verossimilhança (TRV), considerando-se o modelo Gama generalizado por ser caso geral para esses modelos. A metodologia utilizada permitiu ajustar o modelo Exponencial para descrever o progresso da requeima do tomateiro e agrupar os acessos estudados em 10 grupos. O acesso BGH-6 sofreu um progresso de doença menor que os demais, caracterizando-se, assim, sua maior resistência à enfermidade. A regressão inversa possibilitou estimar o tempo até a ocorrência de 5% da severidade da requeima do tomateiro. Pela técnica não-paramétrica de Kaplan-Meier, foi possível estimar as curvas de sobrevivência dos acessos de tomateiro pertencentes aos grupos 1, 2, 4, 6 e 8. Utilizando o teste Logrank, pode-se concluir que a maioria das comparações duas a duas foi significativa (p<0,05), exceto nas comparações dos grupos 2x4, 4x8 e 6x8. O uso dos modelos probabilísticos Exponencial, Weibull e Log-normal possibilitou a estimação das curvas de sobrevivência nos grupos 2, 4, 6 e 8, exceto no grupo 4, em que o modelo Weibull não foi adequado. Comparando os modelos probabilísticos com a técnica não-paramétrica, as curvas dos modelos probabilísticos dos grupos 2 e 4 apresentaram ajustes satisfatórios com relação à curva estimada por Kaplan-Meier.
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FEFEU, SANDRINE. "Structure tridimensionnelle d'une elicitine secretee par phytophthora cryptogea." Paris 6, 1997. http://www.theses.fr/1997PA066077.
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La cryptogeine est une proteine d'environ 10 kda appartenant a la famille des elicitines et secretee par le champignon phytophthora cryptogea. Les elicitines agissent sur des diverses plantes telles que le tabac, la tomate, la pomme de terre, le poivron et le radis. Elles induisent une formation de necroses foliaires dans les tissus de ces plantes ainsi qu'une resistance contre les pathogenes du radis et du tabac. Sur les plants de tabac, la cryptogeine induit une resistance contre le phytopathogene phytophthora nicotianae, agent de la maladie du pied noir. Les structures secondaires de la cryptogeine ont ete identifiees par resonance magnetique nucleaire. La cryptogeine est composee de 5 helices, un petit feuillet antiparallele et comprend trois ponts disulfures. La structure tridimensionnelle de la cryptogeine presente un coeur hydrophobe et une cavite hydrophobe creee par l'agencement du feuillet et d'une boucle. Des etudes comparatives des sequences des elicitines montrent l'importance du residu 13 dans la modulation de l'activite necrotique, ainsi que la conservation des residus formant la cavite hydrophobe. Le residu 13 est expose au solvant et est dans une disposition adequate pour la fixation d'un ligand sans modification structurale. Des spectres roesy hors resonance hsqc ont permis de mesurer les vitesses d'echange des protons amides avec le solvant dans une echelle de temps de l'ordre de la milliseconde. Ces experiences mettent en evidence l'instabilite de deux helices impliquant les residus 86-98 et 22-30. La connaissance de la structure tridimensionnelle de la cryptogeine et la mise en evidence des mouvements qui l'affecte sont des etapes importantes pour mieux comprendre le mecanisme de l'activite biologique des elicitines.
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Hu, Jiahuai. "Phytophthora nicotianae: Fungicide Sensitivity, Fitness, and Molecular Markers." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/26416.
Full textAbstract:
Mefenoxam has been a premier compound for Phytophthora disease control in the nursery industry for 30 years. The primary objectives of this research were to examine whether Phytophthora species have developed resistance to this compound and to investigate fungicide resistance management strategies. Phytophthora nicotianae, a destructive pathogen of numerous herbaceous and some woody ornamental plants, was used as a model system. P. cinnamomi, a major pathogen of a wide range of tree species and shrub plants, was also included for comparison.
Twenty-six isolates of P. nicotianae were highly resistant to mefenoxam with a mean EC50 value of 326.5 µg/ml while the remaining 70 were sensitive with an EC50 of <0.01 µg/ml (Label rate: 0.08µg/ml). All resistant isolates were recovered from herbaceous annuals and irrigation water in 3 Virginia nurseries. Resistant isolates were compared with sensitive ones using seedlings of Lupinus â Russell Hybridsâ in the absence of mefenoxam for relative competitive ability. Resistant isolates out-competed sensitive ones within 3 to 6 sporulation cycles. Resistant isolates exhibited greater infection rate and higher sporulation ability than sensitive ones.
No mefenoxam resistant isolates were identified in P. cinnamomi. All 65 isolates of P. cinnamomi were sensitive to mefenoxam with an EC50 of < 0.04 ï g/ml. Attempts to generate mutants with high resistance to mefenoxam through UV mutagenesis and mycelial adaptation were not successful. However, there were significant reductions in sensitivity to mefenoxam; those slightly resistant mutants carried fitness penalties, which may explain why P. cinnamomi remains sensitive to mefenoxam.
The effect of propamocarb hydrochloride on different growth stages of Phytophthora nicotianae was evaluated in search for an alternative fungicide. Propamocarb greatly inhibited sporangium production, zoospore motility, germination and infection. However, it has little inhibition of mycelial growth and infections. Propamocarb can be used as an alternative fungicide to mefenoxam where mefenoxam resistance has become problematic. However, it must be used preventively; i.e. before infections occur.
The genetic inheritance of mefenoxam resistance in P. nicotianae was studied using F1 progenies of a cross between resistant and sensitive isolates. The F1 progenies segregated for mefenoxam resistance in ratio of 1R:1S, indicating the mefenoxam resistance is controlled by a single dominant gene. One RAPD marker putatively linked to resistant locus in repulsion phase was obtained by bulked segregant analysis and was converted to the SCAR marker. This marker is capable of differentiating mefenoxam resistant populations from sensitive populations included in this study.Ph. D.
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Yang, Xiao. "New Species and Phylogeny of the Genus Phytophthora." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/51184.
Full textAbstract:
The genus Phytophthora includes many agriculturally and ecologically important plant pathogens. Characterization of new Phytophthora species is the first and a most critical step to understanding their biology, ecology and economic importance. Six novel Phytophthora species recovered from irrigation systems at ornamental plant nurseries in Mississippi and Virginia were described based on morphological, physiological and molecular characters:
1. Phytophthora mississippiae sp. nov. produces a mix of non-papillate and semi-papillate sporangia, and catenulate hyphal swellings. It is a heterothallic species. All examined isolates of P. mississippiae are A1. When paired with A2 mating type testers, P. mississippiae produces ornamented oogonia and amphigynous antheridia. It is phylogenetically grouped in Phytophthora subclade 6b based on sequences of the rRNA internal transcribed spacer (ITS) region and the mitochondrially encoded cytochrome c oxidase 1 (cox 1) gene.
2. Phytophthora hydrogena sp. nov. is heterothallic. It produces non-caducous and non-papillate sporangia. It is characterized by frequently producing widening at the pedicel tip of sporangiophores or tapered sporangial based toward the point of attachment. This species is phylogenetically placed in a high-temperature tolerant cluster in Phytophthora clade 9. All members in this cluster grow well at 35 C.
3. Phytophthora virginiana sp. nov. is a self-sterile species. All examined isolates are silent A1. It produces non-caducous and non-papillate sporangia and is also placed in the high-temperature tolerant cluster in clade 9. Morphologically, it is characterized by producing abundant thin-walled, lateral chlamydospores in carrot agar and clarified V8 juice agar.
4. Phytophthora macilentosa sp. nov. is a heterothallic species. Only A1 isolates have been found. It produces characteristic elongated, non-papillate sporangia. It is also a member of the high-temperature cluster in clade 9.
5. Phytophthora stricta sp. nov. is a heterothallic species. It produces unique non-papillate and slightly caducous sporangia with one to three constrictions on its sporangiophore. Phylogenetically, P. stricta represents a new ITS clade within the genus.
6. Phytophthora Xstagnum nothosp. nov. is a novel hybrid species with P. taxon PgChlamydo as its paternal parent and a P. mississippiae-like species as its maternal parent. This new hybrid produces intercalary chlamydospores and catenulate hyphal swellings, which are morphological characters of P. taxon. PgChlamydo and P. mississippiae, respectively. It also produces both smooth-walled and ornamented oogonia, which may be indicative of oogonial characters of its paternal and maternal parents, respectively.
By incorporating new Phytophthora species, clusters and clades, phylogenies including approximately 128 Phytophthora taxa were constructed based on sequences of five genetic markers. Among the selected genetic markers, the beta-tubulin (B-tub) gene provided the highest phylogenetic resolution. General phylogenetic structure of the B-tub phylogeny was similar to that in previous multi-locus phylogenies, except that P. cinnamomi, P. parvispora, P. quercina, P. stricta, and a provisional species, P. sp. e1, were not clustered in any of the 10 known Phytophthora clades and represented new clades. The B-tub phylogeny was also used to study the correlations between phylogeny and morphological characteristics including sporangial papillation, caducity, homothallism, and antheridial configuration, as well as maximum growth temperature. The results indicated that the character of sporangial papillation was mostly consistent among species within individual subclades. Maximum growth temperature was also generally correlated with phylogenetic positions. Consistency in caducity, homothallism or antheridial configuration was not found. A new multi-locus phylogeny based on sequences of 11 genetic markers of more than 146 Phytophthora species was proposed to validate new clades and clusters, as well as investigate detailed phylogenetic relations among species in this quickly expanding, taxonomically complex group of plant pathogens.Ph. D.
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Ludwig, Michael P. "Phytophthora Sojae - Soybean Interaction in a Changing Climate." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1343072645.
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Rivera, Vargas Lydia I. "Possible biochemical mechanisms of pathogenicity in Phytophthora sojae /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu148785431487008.
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Ghimire, Sita Ram. "Diversity in the phytophthora infestans population in Nepal." Thesis, Click to view the E-thesis via HKUTO, 2002. http://sunzi.lib.hku.hk/hkuto/record/B42576751.
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