Auswahl der wissenschaftlichen Literatur zum Thema „Roots (Botany) Diseases and pests“

Phytophthora root rot is one of the most devastating diseases of perennial plants worldwide, affecting plants in food production, amenity plantings and in natural ecosystems. The impact of these diseases in botanic gardens can be substantial and can affect how a site may be used for months and years ahead. Management is critically dependent on avoidance of the introduction of the pathogen and effective hygiene protocols are key to achieving this. Additionally, botanic gardens have a key role to play in protecting plants and enhancing conservation outcomes through surveillance, education and ex situ conservation programmes, as well as through the recognition that they can be critical as sentinel sites to detect new incursions of pests anddiseases. The impact of several Phytophthora species on the in situ and ex situ management of the critically endangered Wollemia nobilis (Wollemi pine), which is highly susceptible to phytophthora root rot, is used to highlight the need to ensure management of these pathogens is a critical component of threatened species recovery and management.

Plant diseases can be traced back almost as far as recorded history. Numerous ancient writings describe plagues and blasts destroying crops and modern civilization still faces many plant disease challenges. Plant pathology has its roots in botany and notable scientists such as Tillet, Prevost, and deBary already had concluded microscopic organisms could cause plant diseases before Robert Koch established the rules of proof of pathogenicity with sheep anthrax. Plant pathologists can be credited with helping improve crop yields and food production throughout the world. However, at a time when there are increasing challenges to crop production, some that potentially may increase the severity or distribution of plant diseases, the training of future plant pathologists appears to be declining, at least in the United States. The ability of the U.S. Land Grant University (USLGU) system to attract and train future generations of plant pathologists may be at risk. Recent data from university plant pathology departments collected by The American Phytopathological Society (APS) documents a decline in the number of students completing advanced degrees in plant pathology, departments with fewer faculty with a diverse expertise in applied plant pathology, fewer stand-alone, single discipline departments of plant pathology, a reduced ability of many departments to offer specific curricular aspects of plant pathology, and a demographic profile that casts an ominous prediction for an unusually large number of faculty retirements over the next decade. The impact of these factors could be a shortage of highly skilled, applied plant pathologists in the U.S. in coming years. The affect also may be felt globally as fewer international students may receive pre-doctoral and post-doctoral training in plant pathology in the U.S. as faculty retire and are not replaced. On the other hand, this likely will create greater opportunities for universities around the world to take leadership in many aspects of plant pathology education. While a decline in students and young faculty trained in applied and field-level specialties of plant pathology (mycology, bacteriology, plant nematology, forest pathology, epidemiology, etc.) is occurring, those trained in the cellular and molecular host-pathogen interactions specialties appear to be increasing. Many plant pathology faculty hired at USLGUs in the last decade are trained in molecular biology and received their Ph.D. degree in a field other than plant pathology. They are now applying those skills to research numerous aspects of host-pathogen interactions of model pathosystems. A shift to a greater research emphasis on molecular host-pathogen interactions over the last decade is evidenced by the number of research articles published in the three APS journals; Plant Disease, Phytopathology and Molecular Plant-Microbe Interactions (MPMI). From 1985 to 2007, there has been a decline in the number of articles published in Plant Disease (–29%) and Phytopathology (–36%) and a steady increase in those published in MPMI since its inception in 1990 (+111%). With new research tools come new research questions. The tools of molecular biology have allowed us to look deeper into questions than ever before and provided us with a perspective not before seen. As we dissect and decode the genomes of the world’s most notorious plant pathogens we get closer and closer to alleviating the global losses and human suffering caused by plant diseases. New “designer crops” with engineered traits for drought and cold tolerance, pest resistance, increased levels of micronutrients, healthier oils such as omega fatty acids, and plant-derived pharmaceuticals are all on the horizon. Research in the future likely will focus on new problems, traditionally seen as outside the discipline of plant pathology. The impact of climate change on plant diseases will be significant. As many parts of the world become warmer and drier some plant diseases likely will increase in severity. Pathogens are likely to migrate and survive in more northern latitudes greatly expanding their range and diseases exacerbated by abiotic stresses such as drought and salinity will increase. Plant pathology will continue to evolve as a multidisciplinary science. These changes will open up many new research opportunities. Plant pathology will play a bigger role in global food security. Research into the molecular and cellular interactions of symbiotic and endophytic organisms will help provide answers to food-borne illnesses caused by E. coli and Salmonella and how these and other human pathogens become established in plants in the field. Plant pathologists will team up with biomedical and aeronautical engineers, nanotechnologists, and computer scientists to develop microsensory technology to detect the introduction and spread of pathogens for biosecurity, diagnostics and epidemiological modeling purposes. Traditional areas of plant disease management and the use of biologicals for disease control also will benefit from a better understanding of the molecular and cellular processes and the similarity of virulence mechanisms and pathogen effectors between plant, insect, and vertebrate pathogens likely will bring new insights into human diseases. And last, but not least, there likely will be a resurgence in plant disease management and epidemiological research as the world’s dependence on biofuels increases and results in new diseases on intensively cultivated plant species used for biomass production.

Increasing demand for wood is putting pressure on forest resources that are equally under threat from insect pests and diseases. Reported average annual forest loss stands at 0.2% globally, 0.8% in Africa, and 1.6% in Kenya. To meet the increasing demand for forest products in Kenya, the government and private sector have established plantations of non-native tree species dominated by Eucalyptus species, Cupressus lusitanica, and Pinus patula. To ensure successful forest plantation establishment and management schemes, there is a need for sufficient knowledge and understanding of tree growth conditions and threats including pests and diseases. This study aimed at determining the incidence of plantation and tree nurseries in Kimondi Forest, Kenya. Tree plantations were mapped into 2.5 Ha rectangular portion transects parallel to the forest roads. In randomly selected portions, observations were carried out for disease and pest signs and symptoms on various tree parts (leaves, stem, roots, fruits, and twigs). In the tree nurseries, 3 m × 1 m rectangular quadrants were placed on seedling beds and similar observations were made. Collected data indicated a high incidence of nursery seedling pests (5.3 % leaves and 5.1% stems) on Eucalyptus species and least on P. patula (2.4% leaves and 3% stems). Higher incidence of plantation pests (35.0% leaves of Eucalyptus sps.) and least on P. patula stems (1.2%) were recorded. On the other hand, twelve (12.0%) of C. lusitanica and (1.8%) Eucalyptus species plantation twigs were infested by pests. A high incidence of nursery seedling disease (9.8%) was observed on C. lusitanica leaves and least on P. patula stems (3.6%). Higher incidence of plantation diseases (32 %) on leaves of Eucalyptus sps. and least on C. lusitanica stem (1.4%) was recorded. In both tree nurseries and plantations, roots and fruits remained free from pests and disease. Major tree pests and diseases identified in Kimondi forests include (Human, wildlife, livestock, Cinara cupressi, Gonipterus scutellatus, Pinus pini, and Leptocybe invasa) and (damping-off, Fusarium wilt, Botryosphaeria canker, cypress canker, and Mycosphaerella spp.) respectively. These results suggest a need for regular monitoring and intervention measures to control pest and disease infestation in the Kimondi forest.

Summary. The large and colourful cut inflorescences of the terminal flowering tropical Grevillea species and hybrids are considered by enthusiasts to have potential as a cutflower crop. Developing understanding of the characteristics of grevillea inflorescences is collated in this review article. Botany, quality, cultivars, production and marketing, physiology and biochemistry, growth and development, flowering regulation, senescence, postharvest losses, pests and diseases, loss reduction measures, and use of floral preservatives for cut inflorescences are discussed. This overview of current knowledge provides a platform for future research and development on this novel native Australian flower.

The bark, leaves, and roots ofAlbizia adianthifoliaare highly sought after in tropical Africa as herbal medicines. Therefore, the aim of this study was to review the botany, medicinal uses, phytochemistry, and pharmacological properties ofA. adianthifoliaso as to provide baseline data required for evaluating the therapeutic potential of the species. Information on the botanical profile, medicinal uses, phytochemistry, and pharmacological properties ofA. adianthifoliawas undertaken using databases such as ScienceDirect, SciFinder, Pubmed, Google Scholar, Medline, SCOPUS, EThOS, ProQuest, OATD, and Open-thesis. Preelectronic literature search of conference papers, scientific articles, books, book chapters, dissertations, and theses was carried out at the University library. Literature search revealed thatA. adianthifoliais used as purgative and herbal medicine for diabetes, eye problems, gastrointestinal problems, haemorrhoids, headache, neurodegenerative disorders, reproductive problems in women, respiratory problems, wounds and pain, skin diseases, sexually transmitted infections, and ethnoveterinary medicine. Phytochemical compounds identified from the species include apocarotenoids, chalcone, dipeptide, elliptosides, essential oils, fatty acids, flavonoids, histamine, imidazolyl carboxylic acid, prosapogenins, steroids, triterpene saponins, and triterpenoids. Pharmacological studies revealed thatA. adianthifoliaextracts and compounds have acetylcholinesterase enzyme inhibitory, anthelmintic, antiamoebic, antibacterial, antimycobacterial, anti-sexually transmitted infections, antifungal, anti-inflammatory, antioxidant, anxiolytic, and antidepressant, cognitive-enhancing, haemolytic, hypoglycemic and antihyperglycemic, immunomodulatory, and cytotoxicity activities. Detailed studies on the pharmacokinetics, in vivo,and clinical research involving compounds isolated fromA. adianthifoliaand extracts of the species are required.

Roots and tubers are one of the most important crops that provide food security in West Africa. Thus, Pachyrhisus erosus with its various potentials, is planned to be introduced in Benin to improve the nutritional quality of the population. Prior to that, this study aimed at assessing pests and disease of P. erosus in the agroecological conditions in the central parts of Benin. Conducted at experimental field in Savè during two consecutive years, experiments were laid in a completely randomized block design with 4 replications and three treatments including EC 533 and EC Kew cultivars of P. erosus and cowpea variety named Kpodji-Guèguè. Results showed that the major pests collected from P. erosus namely Ootheca mutabilis, Medythia quaterna, Piezotrachelus varium, Megalurothrips sjostedti and Brevipalpus phoenis were not so far reported in it. Compared to cowpea, pest’s infestation and their damages were lower on P. erosus. Infestation severity on leaves and the percentage of perforated green pods ranged from 0.7% to 3% against 0.8% to 88.9% and from 12.5% to 16% against 57.2% to 64% respectively on P. erosus and cowpea. Cercospora disease caused by Cercospora canescens and yam bean leaf blight caused by an unknown fungus were observed. Cercospora disease affected cowpea and P. erosus while yam bean leaf blight affected only P. erosus. This study provides additional data on pests and diseases associated with P. erosus worldwide and alerts farmers regarding their management.

Coffea arabica is susceptible to several pests and diseases, some of which affect the leaves and roots. Systemic acquired resistance (SAR) is the main defence mechanism activated in plants in response to pathogen attack. Here, we report the effects of benzo(1,2,3)thiadiazole-7-carbothioic acid-s-methyl ester (BTH), a SAR chemical inducer, on the expression profile of C. arabica. Two cDNA libraries were constructed from the mRNA isolated from leaves and embryonic roots to create 1587 nonredundant expressed sequence tags (ESTs). We developed a cDNA microarray containing 1506 ESTs from the leaves and embryonic roots, and 48 NBS-LRR (nucleotide-binding site leucine-rich repeat) gene fragments derived from 2 specific genomic libraries. Competitive hybridization between untreated and BTH-treated leaves resulted in 55 genes that were significantly overexpressed and 16 genes that were significantly underexpressed. In the roots, 37 and 42 genes were over and underexpressed, respectively. A general shift in metabolism from housekeeping to defence occurred in the leaves and roots after BTH treatment. We observed a systemic increase in pathogenesis-related protein synthesis, in the oxidative burst, and in the cell wall strengthening processes. Moreover, responses in the roots and leaves varied significantly.

Sweetpotato (Ipomea batatans) is a food crop of global significance. The storage roots and foliage of crop are attacked by a wide range of pests and diseases. Whilst these are generally well controlled in developed countries using approaches such as clean planting material and monitoring with pheromone traps to guide insecticide use, research into methods suitable for developing countries has lagged. In Papua New Guinea (PNG), sweetpotato is grown extensively as a subsistence crop and commercial production as a cash crop is developing. We report results from a survey of 33 smallholder producers located in the Highlands of PNG where the crop is of particular importance. Surveys of interviewees’ crops showed high levels of pest and disease impact to foliage, stems and storage roots, especially in crops that were several years old. Weevils (Curculionidae) were reportedly the most damaging pests and scab (caused by the fungusElisnoe batatus) the most damaging disease. Most producers reported root damage from the former and foliar damage from the latter but the general level of knowledge of pest and disease types was low. Despite the apparency of pest and disease signs and symptoms and recognition of their importance by farmers, a large majority of producers reported practiced no active pest or disease management. This was despite low numbers of farmers reporting use of traditional cultural practices including phytosanitary measures and insecticidal plants that had the scope for far wider use. Only one respondent reported use of insecticide though pesticides were available in nearby cities. This low level of pest and disease management in most cases, likely due to paucity in biological and technical knowledge among growers, hampers efforts to establish food security and constrains the development of sweetpotato as a cash crop.

Abstract Sustainable production of orchids may be achieved with the use of symbiotic microorganisms that improve resistance of plants to pests and diseases and reduce the need of substrate fertilization. In this study, one fungus (F1), one yeast (Y1) and one gram-positive bacteria (B+) were isolated from the roots of the orchid Oncidium varicosum and used in the cultivation of protocorms and plantlets obtained from seeds of this species. Cultivation of protocorms in Murashige and Skoog (MS) medium enriched with sucrose and inoculated with microorganisms did not result in better development of protocorms. However, the use of plantlets in the rooting phase in MS medium without sucrose and inoculated with B+ resulted in plantlets with more leaves and roots and longer shoots and roots, suggesting synergism between microorganism and plant when sucrose is absent. The major benefits of co-cultivating plantlets and these microorganisms were observed in the acclimatization in the greenhouse. Plantlets obtained with oat meal agar medium and B+ showed the highest pseudobulb diameter, number of roots, height and fresh weight among treatments. We concluded that the application of rooting-derived microorganisms in the in vitro culture and plantlet acclimatization of Oncidium varicosum is beneficial.

Multiple stresses almost always have synergistic effects on plants. In citrus, there are direct and indirect interactions between salinity and other physical abiotic stresses like poor soil drainage, drought, irradiance, leaf temperature, and atmospheric evaporative demand. In addition, salinity interacts with biotic pests and diseases including root rot (Phytophthora spp.), nematodes, and mycorrhizae. Improving tree water relations through optimum irrigation/drainage management, maintaining nutrient balances, and decreasing evaporative demand can alleviate salt injury and decrease toxic ion accumulation. Irrigation with high salinity water not only can have direct effects on root pathogens, but salinity can also predispose citrus rootstocks to attack by root rot and nematodes. Rootstocks known to be tolerant to root rot and nematode pests can become more susceptible when irrigated with high salinity water. In addition, nematodes and mycorrhizae can affect the salt tolerance of citrus roots and may increase chloride (Cl-) uptake. Not all effects of salinity are negative, however, as moderate salinity stress can reduce physiological activity and growth, allowing citrus seedlings to survive cold stress, and can even enhance flowering after the salinity stress is relieved.

Boschniakia hookeri Walpers has been found to parasitize the roots of Gaultheria shallon Pursh, Arctostaphylos uva-ursi (l.) Spreng, and Vaccinium ovatum Pursh, all members of the Ericaceae. This is the first documented report of the parasitism of Vaccinium ovatum. The subterranean shoot of B. hookeri originates endogenously from the perennial tubercle of the parasite. The shoot has an eustele, composed of collateral vascular bundles, arranged in four composite fronts and separated by four wide 'leaf gaps.' Pits on metaHylem vessels range from nearly circular to laterally elongated. Rll vessel members have simple perforations. Ouerall, the Hylem of subterranean shoots contained relatively few tracheary elements. Phloem is abundant, with radial series of sieve tube members that have simple sieve plates. Brachysclereids forming large clusters are positioned to both the inside and outside of the vascular bundles. Abundant stomata are present and frequently raised above the shoot surface. RHillary buds along subterranean shoots are capable of producing flowers or branch shoots. Considerable secondary growth occurs in maintained shoots below developing branch shoots. This manifested by the additional production of secondary Hylem and phloem, and the formation of a protective cuticular epithelium. This study of B. hookeri supports the view that the short and fleshy character of the subterranean shoot, increased presence of phloem, reduction of leaves to scales, and a perennial nature are specializations associated with the holoparasitic mode of life.

South Africa has the highest species diversity of ericaceous plants belonging to the Erica genus. There are over 850 identified species in the Cape Floral Region. The Albany Centre of Endemism (ACOE) is located within this region and is a hotspot of diversity consisting of various plant genera. The success of Erica plants is ubiquitously attributed to mycorrhizal relationships they engage in with a diverse group of fungi. This symbiosis is known as the ericoid mycorrhizal (ERM) association. The overall aim of this study was to establish the diversity of root fungi associated with Erica plants using morphological, molecular and 454 pyrosequencing techniques. Six Erica species were identified using leaf and flower morphology according to taxonomic keys. The identified plants were Erica cerinthoides, Erica demissa, Erica chamissonis, Erica glumiflora, Erica caffra and Erica nemorosa. Roots from sampled plants were stained and examined microscopically to determine their mycorrhizal status. Ericoid mycorrhizal associations together with dark septate endophyte (DSE) structures and hyphae that did not form any specific structure were observed in all the roots. In addition arbuscular mycorrhizal (AM) structures in the form of vesicles were detected in E. glumiflora and E. cerinthoides. In order to identify the culturable fungi associated with the respective hosts, sterilised roots were placed on various culture media for cultivation. Thereafter isolated fungi were morphologically classified into 67 morphotypes. These were mostly sterile and darkly pigmented. Non-sporulating mycelia of variable colouration such as white, cream-yellowish, beige, green and brown were also observed. Further identification was carried out using molecular techniques. DNA was extracted separately from pure cultures and amplified using ITS1 and ITS4 primers in a polymerase chain reaction (PCR). Thereafter sequencing and Basic Local Alignment Search Tool (BLAST) were used to identify the isolates to generic level. The fungi were taxonomically classified into 54 operational taxonomic units and 94 percent were Ascomycetes and Helotiales was the dominant order. Unclassified Helotiales with affinities to fungi currently identified as Epacrid root fungus was common in all hosts. Other isolates that were identified included Oidiodendron, Meliniomyces, Phialocephala, Cadophora, Lachnum, Leohumicola Cryptosporiopsis, Chaetomium, Acremonium and Epicoccum species. Basidiomycetes were represented by two OTUs belonging to the genus Mycena. Four OTUs comprised fungi that had no significant alignments in the reference databases. Direct root DNA extraction together with 454 pyrosequencing was used to detect the diversity of culturable and unculturable fungi associated with the identified hosts. The ITS2 region was targeted for sequencing. Although Ascomycetes remained the dominant phyla, Basidiomycetes were also detected in all host plants. Glomeromycota was present in E. caffra and E. cerinthoides. Helotiales was dominant in all Erica plants with the exception of E. cerinthoides and E. chamissonis which were dominated by the order Chaetothyriales. The OTUs identified to genus level included Epacris pulchella root fungus, Oidiodendron cf. maius, Acremonium implicatum, Leohumicola, Lachnum, Capronia and Mycena species. Culture-based techniques and pyrosequencing detected similar fungal composition comprising Ascomycetes, while, pyrosequencing was able to detect Glomeromycetes and Basidiomycetes.

Thesis (MScAgric)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: Characterizing the genetic structure of a pest population can provide an understanding of the factors influencing its evolution and assist in its ultimate control. The aim of the present study was to characterize the genetic structure of woolly apple aphid Eriosoma lanigerum (Hausmann) populations in the Western Cape Province in South Africa. Since this economically important apple pest has not previously been characterized at molecular level, it was necessary to evaluate methods for determining the genetic structure of E. lanigerum populations. Two different molecular techniques were evaluated viz. random amplification of polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP). This study represents the first application of the latter technique to members of the Aphididae. Aphids were sampled from four regions in the Western Cape in South Africa viz. Elgin, Ceres, Vyeboom and Villiersdorp. A spatially nested sampling design was used to establish the distribution of the genetic variance of aphids. A total of 192 individuals from 13 farms were analysed. Ten RAPD primers were chosen for analysis from an initial assay of 25 after fragment reproducibility had been confirmed. For AFLP analysis three different rare-cutting restriction enzymes were evaluated for AFLP analysis, viz. EcoRI, SseI and MluI. The latter yielded the best results in combination with the frequent-cutting enzyme MseI. Twenty-five AFLP selective primer pairs were evaluated, out of which five were chosen for analysis of the total population. Two hundred and fifty AFLP fragments and 47 RAPD fragments were scored for analysis. Both analyses indicated that a low level of genetic variation was apparent in E. lanigerum populations and that no differentiation resulted from geographic isolation. From RAPD analyses it was deduced that all variation could be attributed to differences between individuals. AFLP analysis indicated that, whereas genetic differences in E. lanigerum populations between orchards were negligible, a significant portion of genetic variation could be attributed to differences between farms and individuals within farms. Therefore, AFLP analysis allowed for finer discrimination of the genetic structure of E. lanigerum populations than RAPD analysis and is recommended for studies of other aphid species. The fact that most of the genetic variation present in E. lanigerum populations could be found on small spatial scales indicated that sampling individuals over a wide geographic area was an ineffective way of detecting the genetic diversity present in E. lanigerum populations. The low level of variation in populations is most likely due to the exclusive occurrence of parthenogenetic reproduction, founder effects (including distribution of infested plant material from a limited source) and selective factors such as the use of resistant rootstocks or pesticides. Furthermore, the low level of variation found indicated that the possibility of controlling E. lanigerum in the Western Cape using host plant resistance is favourable. Thus, plant breeders developing resistance to E. lanigerum can expect plant entries to be exposed to most of the genetic diversity present in Western Cape populations, regardless of location.
AFRIKAANSE OPSOMMING: Die bepaling van die genetiese struktuur van 'n landboukundige plaagpopulasie kan lei tot begrip van die faktore wat die populasie beïnvloed en kan uiteindelike beheer vergemaklik. Die doel van die huidige studie was om die genetiese struktuur van die appelbloedluis Eriosoma lanigerum (Hausmann) in die Wes-Kaap Provinsie van Suid-Afrika te bepaal. Aangesien hierdie belangrike appelplaag nie van tevore op molekulêre vlak bestudeer is nie, was dit nodig om metodes vir die bepaling van die genetiese struktuur van E. lanigerum populasies te evalueer. Twee molekulêre tegnieke is geëvalueer, nl. lukraak geamplifiseerde polimorfiese ONS (RAPD) en geamplifiseerde fragment-lengte polimorfismes (AFLP). Hierdie studie is die eerste om laasgenoemde tegniek te gebruik om lede van die Aphididae te bestudeer. Plantluise is verkry van vier verskillende gebiede in die Wes-Kaap Provinsie van Suid-Afrika nl. Elgin, Ceres, Vyeboom en Villiersdorp. 'n Hierargiese sisteem is gebruik om die verspreiding van die genetiese variasie van plantluise te bepaal. In totaal is 192 individue van 13 plase geanaliseer. Tien RAPD inleiers is gekies uit 'n analise van 25 verskillende inleiers nadat fragment reproduseerbaarheid bevestig is. Drie verskillende restriksie ensieme is geëvalueer vir AFLP analise nl. EcoRI, SseI en Mlul. Die beste resultate is verkry toe MluI saam met MseI gebruik is. Vyf-en-twintig AFLP selektiewe inleier pare is geëvalueer waarvan vyf gekies is vir analise van die totale populasie. Twee-honderd-en-vyftig AFLP fragmente en 47 RAPD fragmente is gedokumenteer vir analise. Beide RAPD en AFLP analises het getoon dat daar 'n lae vlak van genetiese variasie in E. lanigerum populasies is en dat geen differensiasie as gevolg van geografiese isolasie ontstaan het nie. Uit RAPD analise is daar afgelei dat al die variasie toegeskryf kon word aan verskille tussen individue. AFLP het aangetoon dat alhoewel verskille in E. lanigerum populasies tussen boorde laag was, kon 'n hoë persentasie van die variasie toegeskryf word aan verskille tussen plase en individue binne plase. AFLP analise het meer insig in die genetiese struktuur van E. lanigerum populasies verskaf, en word dus aanbeveel vir studies van ander plantluise. Omdat meeste van die genetiese variasie oor klein geografiese afstande verkry word, is steekproefueming oor groot gebiede 'n ondoeltreffende manier om die genetiese variasie binne 'n monster te meet. Die lae vlak van genetiese variasie is waarskynlik te wyte aan partenogenetiese vermeerdering, stigter gevolge (insluitend verspreiding van geïnfesteerde plantmateriaal vanaf 'n beperkte bron), sowel as selektiewe faktore soos die gebruik van bestande onderstokke en insekdoders. Verder dui die lae vlak van variasie aan dat die moontlikheid vir beheer deur gasheerplantbestandheid goed is in die Wes-Kaap. Planttelers kan verseker wees dat hulle plante blootgestel sal wees aan meeste van die genetiese variasie in die Wes-Kaap appelbloedluis populasies ongeag hulle ligging.

Studies were conducted on three field trials of wheat cv. Kopara to investigate the lack of compensation by later determined components of yield because of early disease constraints. The investigation was based on the hypothesis that early disease reduces root development and thus causes the plants to be water constrained at later growth stages when soil water deficits usually occur. The reduced root development and soil water deficits may reduce the ability of the plant to compensate for reductions in early determined components. The hypothesis was tested by the application of irrigation to alleviate water stress. In a disease free crop, the possible phytotonic effects of the fungicides benomyl and triadimefon on wheat were investigated. These fungicides had no phytotonic effects on shoot, root growth, or yield under the prevailing conditions. The effect of disease on root development was analysed by root length measurements. Disease present in the crop at any stage of growth affected root development. Root development in the upper zones of the soil profile was reduced more by disease compared to those zones below 35 cm. A full disease epidemic reduced root development more than an early or late disease epidemic. The early and late disease epidemics had similar effects on root length. Alleviation of early disease constraints enabled greater development of roots to offset any earlier reductions. Soil water deficits increased root development in the lower zones of the nil disease plants. The presence of adequate soil water from irrigation reduced the requirement for further root growth in all treatments. In the 1981-1982 field trial a full disease epidemic reduced yield by 14% whereas an early disease epidemic reduced yield by 7%. The reduction in yield was attributed to a lower grain number. With irrigation the yield reduction in the full disease plants was 12% whereas in the early disease plants the reduction was only 2.4%. This indicated that plants affected by the early disease epidemic were water constrained. In this study, the results suggested that, for conditions prevailing in Canterbury, the supply of water at later growth stages increased grain weight in plants which were subject to early disease epidemics. This suggests that reduced root development caused by early disease and soil water deficits may prevent compensation by grain weight. Water use was similar in all disease treatments. After irrigation the irrigated plants of all treatments used more water. Disease affected water use in relation to yield production however, and was better expressed by water use efficiency. Water use efficiency was reduced in the full disease plants. A stepwise regression analysis suggested that water use efficiency was affected directly by disease at later growth stages, and indirectly via an effect on total green leaf area at early growth stages. This study partially proves the hypothesis that reductions in root development caused by an early disease epidemic may constrain the plants at later growth stages when water deficits usually occur. It was shown that the reduction in root development caused by disease could be counteracted by irrigation. In this respect, water served as a tool to study the effect of disease constraints on the yield of wheat. A knowledge of cereal crop physiology, root growth and function is used to explain and discuss the observations made in this research programme. The results are discussed in relation to the way in which disease affects yield through its effect on root development. The possible reasons for the continued effects of disease even after the control of disease at later growth stages are discussed. The economic use of fungicides and water in diseased crops are also outlined. Suggestions for future studies on disease-yield loss relationships are provided. The repetition of these experiments in different sites and climatic regions could provide information which may be incorporated in disease-yield loss simulation models. This could then be used to predict root development and water requirements of diseased plants, and provide a basis for economic use of fungicides and water, and for better disease management programmes.

Cylindrocladium black rot (CBR) is a destructive root disease of peanut caused by Cylindrocladium crotalariae. New and quantitative approaches were developed to estimate the inoculum potential for this soil-borne pathogen under soil-temperature tank conditions favorable for CBR development. Using cultural plating methods, numerous Q. crotalariae infections (1 to > 1,000 per plant) were observed on asymptomatic root systems of peanut plants, susceptible and resistant to CBR, grown in naturally infested soils at 25 C. Regression-line slope values of log10-log10 plots for microsclerotial inoculum density versus the number of observed root infections per plant and per unit root length [0.98 (R2 =0.94) and 0.99 (R2 = 0.94), respectively] indicated direct proportionality between the respective variables. Efficiency of inoculum for observed infection (percent of germinating microsclerotia that infect roots) estimates were high (near 100%), while efficiency of observed infection for necrosis (percent of infections that develop into necroses) estimates were low (0.27 to 0.28%). Observed infection observed infections per m root per day per rates, I 0 r (the number of microsclerotium per g of soil) were significantly lower (P = 0.001) for CBR-resistant 'Spancross• than for CBR-susceptible 'Florigiant•. The majority of observed infections did not appear to be restricted to outer cortical root tissues. A portion of observea infections near root surfaces resulted in subsequent colonization of the inner cortex and stele of plants for each cultivar. A significantly greater (P = 0.05) number of segments from steles of CBR-susceptible Florigiant taproots were colon~zed by Q. crotalariae than those from CBR-resistant Spancross. Using naturally infested peanut field soils, a dose of 7.4 )-lg NaN3 (sodium azide)/g soil was effective in reducing initial microsclerotial populations by 50%, based upon a highly significant dosage-response curve (R2 = 0.96, P = 0.0001). CBR development was reduced significantly (P = 0.05) for Florigiant plants grown in Q. crotalariae-infested soils treated with 7.5 fl' NaN3/g soil or higher, compared to plants grown in untreated soils. Sublethal doses of NaN3 combined with biological control agents may be useful in the development of integrated CBR control measures.
Ph. D.

Thesis (MScAgric)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: Soilborne diseases of grapevines represent a complex problem with limited information available, both locally and internationally. Previous research in South Africa indicated that Phytophthora and Pythium spp. were the most widespread and devastating pathogens in grapevine nurseries and vineyards in the Western Cape province. The local grapevine industry is currently expanding; new cultivars, methods and agricultural chemicals are being used which can affect soilborne pathogens. It has therefore become necessary to reassess the status of soilborne pathogens in nurseries, since information in this regard is crucial for the development of disease management practices for the expanding local grapevine industry. Soilborne fungal genera associated with roots and crowns of declining nursery grapevines were assessed in surveys conducted at three different grapevine nurseries in the Western Cape province. Cylindrocarpon, Fusarium, Pythium, and Rhizoctonia spp. were consistently isolated from roots and crowns of declining nursery grapevines. Cylindrocladiella spp. and Phytophthora cinnamomi were infrequently isolated from diseased roots, crowns and soil whereas Pythium spp. were abundant in most of the soils. Results suggest that the status of soilborne fungal pathogens in grapevine nurseries in the Western Cape province has changed over the last 30 years. The DNA phylogeny and pathogenicity of the isolates of Cylindrocladiella were determined. Four species of Cylindrocladiella occur on grapevines in South Africa, namely C. lageniformis, C. parva, C. peruviana, as well as a new species, described in this study as C. viticola, which forms part of the C. infestans species complex. Pathogenicity trials were inconclusive. Ten Fusarium spp. were isolated from roots and crowns of declining nursery grapevines, namely F. acuminatum, F. anthophilum, F. chlamydosporum, F. equiseti, F. nygamai, F. oxysporum, F. proliferatum, F. scirpi, F. semitectum and F. solani. The dominant species was F. oxysporum, followed by F. proliferatum and F. solani. In pathogenicity trials F. oxysporum and F. solani significantly reduced root volume, root dry mass, length of new shoots, stem diameter and number of leaves, but increased the percentage of chlorotic leaves and root rot severity. Fusarium proliferatum also caused a significant reduction in new shoot growth, number of leaves and increased root rot severity compared to the controls. Fusarium so/ani seems to be more virulent than F. oxysporum, followed by F. pro/iferatum. This is the first report of F. oxysporum, F. pro/iferatum and F. so/ani as pathogens of grapevines in South Africa, and the first report of F. proliferatum as a pathogen of grapevines in the world. Phytophthora cinnamomi was isolated at low frequencies from declined grapevines, although present in the rhizosphere soil. It is possible that the extensive use of downy mildew chemicals in grapevine nurseries may protect grapevines from infection by P. cinnamomi. The effect of chemicals used to combat downy mildew on Phytophthora root rot of nursery grapevines was evaluated in a glasshouse. There was very little discernable effect of the chemicals tested relative to the control plants for the parameters measured and it was concluded that the inoculation technique needed refinement. However, plants treated with phosphorous acid tended to be taller and have more leaves, greater stem diameter and root volume than controls or plants treated with the other chemicals. The data obtained in this study are not conclusive, but indicated certain trends that more glasshouse trials and field trials would resolve. Results presented in this thesis indicate that a major shift has occurred in the status of soilborne fungi associated with roots and crowns of grapevines in nurseries in the Western Cape since the 1970s when Phytophthora and Pythium were predominant. The prevalence and role of soilborne fungi need to be determined so that new appropriate disease management strategies can be developed to limit losses in grapevine nurseries and ensure the sustainable production of healthy plants for the grapevine industry.
AFRIKAANSE OPSOMMING: 'N ONDERSOEK NA GRONDGEDRAAGDE SWAMME GEASSOSIEER MET WORTELS EN KRONE VAN WINGERD IN KWEKERYE Grondgedraagde siektes van wingerd is 'n komplekse probleem waaroor min inligting, beide plaaslik en internasionaal, beskikbaar is. Vorige navorsing in Suid-Afrika het aangedui dat swamme van die genera Phytophthora en Pythium die mees algemene en vernietigende grondgedraagde patogene in kwekerye en wingerde in die Wes-Kaap provinsie is. Die plaaslike wingerdbedryf brei huidiglik uit; nuwe kultivars, metodes en landbouchemikalieë word gebruik wat 'n invloed kan hê op grondgedraagde patogene. Gevolglik het dit noodsaaklik geword om die status van grondgedraagde patogene in wingerdkwekerye weer te bepaal, aangesien inligting in hierdie verband noodsaaklik is vir die ontwikkeling van siekte bestuurspraktyke vir die ontwikkelende plaaslike wingerdbedryf. Grondgedraagde swamgenera geassosieer met wortels en krone van terugsterwende wingerd in kwekerye is bepaal in opnames wat by drie verskillende wingerdkwekerye in die Wes-Kaap provinsie uitgevoer is. Cylindrocarpon, Fusarium, Pythium, en Rhizoctonia spp. is konstant vanuit wortels en krone van terugsterwende wingerdplante in kwekery geïsoleer, Cylindrocladiella spp. en Phytophthora cinnamomi is ongereeld vanuit siek wortels, krone en grond geïsoleer, terwyl Pythium spp. algemeen in meeste gronde voorgekom het. Resultate dui daarop dat die status van grondgedraagde swampatogene in wingerdkwekerye in die Wes- Kaap provinsie oor die laaste 30 jaar verander het. Die DNA filogenie en patogenisiteit van die isolate van Cylindrocladiella is bepaal. Vier spesies van Cylindrocladiella kom voor op wingerd in Suid-Afrika, naamlik C. lageniformis, C. parva, C. peruviana, sowel as 'n nuwe spesie, wat in hierdie studie as C. viticola aangedui is en wat deel is van die C. infestans spesie kompleks. Patogenisiteits proewe was onvoldoende om die patogeniese status van die swam me te bepaal. Tien Fusarium spp. is vanuit wortels en krone van terugsterwende wingerdplante in kwekery geïsoleer, naamlik F. acuminatum, F. anthophilum, F. chlamydosporum, F. equiseti, F. nygamai, F. oxysporum, F. proliferatum, F. scirpi, F. semitectum en F. solani. Die dominante spesies was F. oxysporum, gevolg deur F. proliferatum en F. solani. In pathogenisteitsproewe het F. oxysporum en F. solani gelei tot 'n betekenisvolle laer wortelvolume, droë massa van wortels, lengte en droë massa van nuwe groei en aantal blare, maar het die persentasie chlorotiese blare en graad van wortelvrot verhoog. Fusarium proliferatum het ook gelei tot 'n betekenisvolle afname in lengte en massa van nuwe groei, aantal blare en 'n verhoogde graad van wortelvrot in vergelyking met die kontrole behandelings. Dit wil voorkom asof Fusarium solani meer virulent is as F. oxysporum, gevolg deur F. proliferatum. Hierdie is die eerste aanmelding van F. oxysporum, F. proliferatum en F. solani as patogene van wingerd in Suid-Afrika, en die eerste aanmelding van F. proliferatum as 'n patogeen van wingerd in die wêreld. Phytophthora cinnamomi is konstant teen lae frekwensies vanuit terugsterwende wingerd in kwekerye geïsoleer, alhoewel dit in risosfeer gronde teenwoordig was. Dit is moontlik dat die ekstensiewe gebruik van chemikalieë teen donsskimmel in wingerdkwekerye die wingerdplante kan beskerm teen infeksie deur P. cinnamomi. Die effek van chemikalieë wat gebruik word teen donsskimmel op Phytophthora wortelverrotting van wingerd in kwekerye, is 'n glashuis geëvalueer. Die chemikalieë wat gestoets is, het vir die gemete parameters, tot baie min onderskeibare effek gelei relatief tot die kontrole plante, en daar is afgelei dat die inokulasie tegniek verbetering benodig. Plante wat met fosforiensuur behandel is, het egter geneig om langer te wees met meer blare, 'n groter stamdeursnee en wortelvolume as kontrole plante of plante behandel met ander chemikalieë. Data verkry vanuit die hierdie studie was onvoldoende, maar sekere neigings is aangedui wat deur verdere glashuis- en veldproewe verklaar sal word. Resultate wat in hierdie tesis weergegee is, het aangedui dat 'n algehele verskuiwing in die status van grondgedraagde swamme geassosieer met wortels en krone van wingerd in kwekerye vanaf die 1970s, toe Phytophthora en Pythium die dominante genera was, plaasgevind het. Die voorkoms en rol van grondgedraagde swamme moet bepaal word, sodat nuwe voldoende siektebestuurspraktyke ontwikkel kan word om verliese in wingerdkwekerye te beperk en sodoende die volhoubare produksie van gesonde plante vir die wingerdbedryf te verseker.

Thesis (MSc)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Two genera of ophiostomatoid fungi occur in the seed-bearing structures of serotinous Protea species in the Cape Floristic Region. These fungi are dispersed by arthropods, including mites and beetles that visit the Protea host plants. Although the vectors of Proteaassociated ophiostomatoid fungi are known, their dispersal patterns remain unknown – especially the manner in which recently burnt fynbos vegetation is recolonized. Additionally, their reproduction strategy has not previously been investigated. The focus of this study was, therefore, to determine the extent of within- and between-plant dispersal of Proteaassociated ophiostomatoid fungi at the population level and to investigate their reproductive strategy. One Protea-associated ophiostomatoid fungus, Knoxdaviesia proteae, is found exclusively in the fruiting structures of P. repens and was the focus of this study. In order to interrogate natural populations of this fungus, 12 polymorphic microsatellite markers specific to K. proteae were developed with an ISSR-PCR enrichment strategy and pyrosequencing. These markers were amplified in two distantly separated populations of K. proteae. The genetic and genotypic diversities of both populations were exceptionally high and neither showed significant population differentiation. The lack of population structure in both populations implies that K. proteae individuals within a P. repens stand are in panmixia. As one of the sampling sites had burnt recently, the process whereby young fynbos is recolonized could be investigated. Compared to the adjacent, unburnt area, K. proteae individuals in the burnt area of this population had significantly less private alleles, suggestive of a young population that had experienced a genetic bottleneck. Knoxdaviesia proteae individuals that did not originate from the adjacent unburnt area were encountered within the burnt site and, additionally, isolation-by-distance could not be detected. The parsimony-based haplotype networks and the tests for linkage disequilibrium indicated that recombination is taking place within as well as between the two distantly separated populations. The observed panmixia in P. repens stands, widespread recolonization and the high genetic similarity and number of migrants between the two populations emphasizes long-distance dispersal and therefore the role of beetles in the movement of K. proteae. This cohesive genetic structure and connection across large distances is likely a result of multiple migration events facilitated by beetles carrying numerous phoretic mites.
AFRIKAANSE OPSOMMING: Twee genera ophiostomatoid swamme kom in die saad-draende strukture van bloeiende Protea spesies in the Kaapse Floristiese Streek voor. Hierdie Protea-verwante ophiostomatoid swamme word gekenmerk deur hul assosiasie met geleedpotige vektore – spesifiek die myt en kewer besoekers van die Protea gasheer plante. Alhoewel die geleedpotige vektore van Protea-verwante ophiostomatoid swamme bekend is, is die wyse waarop hierdie swamme versprei onbekend; veral die manier waarop onlangse gebrande fynbos geherkoloniseer word. Verder is die voortplantings-strategie van hierdie swamme nog nie voorheen ondersoek nie. Die fokus van hierdie studie was dus om die omvang van binne- en tussen-plant verspreiding van Protea-verwante ophiostomatoid swamme te bepaal op die populasie vlak en om hul voorplantings-strategie te ondersoek. Een Protea-verwante ophiostomatoid swam, Knoxdaviesia proteae, word uitsluitlik in die vrugdraende strukture van P. repens aangetref en was die fokus van hierdie studie. Om natuurlike populasies van hierdie swam te ondersoek is 12 mikrosatelliet-merkers spesifiek vir K. proteae ontwerp deur ‘n ISSR-PCR strategie en “pyro”-basisvolgorde bepaling te gebruik. Hierdie merkers is geamplifiseer in twee K. proteae populasies wat ver van mekaar geskei is. Die genetiese en genotipiese diversiteit van beide populasies was uitsonderlik hoog en nie een het beduidende populasie-differensiasie getoon nie. Die gebrek aan populasie struktuur in beide populasies veronderstel dat K. proteae individue binne ‘n P. repens stand in panmiksia is. Aangesien een van die steekproef terreine onlangs gebrand het, kon die herkolonisasie proses van jong fynbos ondersoek word. In vergelyking met die aangrensende, ongebrande area, het K. proteae individue in die gebrande area beduidend minder private allele gehad. Dit dui op ‘n jong populasie wat ‘n genetiese bottelnek beleef het. Knoxdaviesia proteae individue wat nie van die aangrensende, ongebrande area afkomstig is nie is ook binne die gebrande terrein aangetref. Verder is afsondering-deur-afstand nie aangetref nie. Die parsimonie-gebaseerde haplotiepe-netwerke en die toetse vir koppeling-onewewigtigheid het aangedui dat rekombinasie binne sowel as tussen die twee populasies plaasvind. Die panmiksia wat waargeneem is in P. repens populasies, wydverspreide herkolonisasie en die hoë genetiese ooreenkoms en hoeveelheid immigrante tussen die twee populasies beklemtoon lang afstand verspreiding en dus die rol van kewers in die beweging van K. proteae. Hierdie samehangende genetiese struktuur en die verband oor groot afstande is waarskynlik ‘n gevolg van verskeie migrasies gefasiliteer deur kewers wat talle foretiese myte dra.

Bacterial galls on Douglas-fir (Pseudotsuga menzeisii [Mirb.] Franco), collected from the southern tip of Vancouver Island, the Greater Vancouver area and the Hope region of British Columbia, were generally globose in shape with rough, irregular surfaces and measured between 0.5 and 2.0 cm in diameter. The galls were generally located on the tips of branches or twigs of 10- to 20-year old Douglas-fir trees. The bacterial gall disease appeared to affect few Douglas-fir trees in the collection areas and bacterial galls were not found on any other coniferous species. Furthermore, there have been no reports of serious damage to natural forests in British Columbia due to bacterial gall disease. Young, greenhouse-grown Douglas-fir seedlings occasionally died if the tip of the main stem was artificially inoculated. Often new growing tips would be produced affecting the growth form of the seedlings. Two types of gall-forming Erwinia spp. were isolated from Douglas-fir galls. Typical isolates, tentatively identified by fatty acid analysis as Erwinia salicis, produced galls which were rough and irregular in shape composed of multiple outgrowths marked by a single or cross-shaped fissure. The atypical isolate, tentatively identified by fatty acid analysis as Erwinia herbicola subsp. herbicola, produced galls which were smooth and generally round in shape with the surface cracking as the gall expanded. Colonies of the typical isolates grown on casein-peptone-glucose media were characteristically round, slightly domed with somewhat concentric ridging observed near the margins of the colonies. Three to 4 day old colonies of the atypical isolates grown on casein-peptone-glucose media were characteristically round and concave while older colonies produced an extracellular slime and were more irregular in shape. In Luria Broth, the typical isolates grew at temperatures of up to 32°C while the atypical isolate grew at temperatures of up 34°C. The typical isolate was resistant to a wider range of antibiotics than the atypical isolate. Polyclonal antisera were produced against glutaraldehyde-fixed whole cells of both the typical T-2789 and atypical A-0181 gall-forming Erwinia isolates. The purified antisera were isolate specific as tested by immunodiffusion and an indirect ELISA against several different phytopathogenic bacteria including Pseudomonas syringae pv. syringae, Erwinia herbicola subsp. herbicola, Agrobacterium tumefaciens, Rhizobium leguminosarum and Erwinia carotovora subsp. carotovora. Plasmid profiles of the typical Erwinia isolates contained one band while the atypical isolate characteristically contained 4 to 5 bands which appeared to be different forms of at least one plasmid. Restriction digests of the typical isolates suggested a size of approximately 50 kb while complex digestion profiles were obtained for the atypical isolates because of the difficulty in isolating individual plasmid types. From visual estimates against Hindlll-digested lambda DNA, a size of between 10 and 20 kb was suggested for the fastest moving plasmid band of the atypical isolate. No homology was observed between the different plasmid types characteristic of the two isolates. The role of the plasmid DNA of the atypical isolate in pathogenesis was not determined because curing of the plasmid(s) was not successful using high temperature treatments plus chemical curing agents. Heat treatment experiments, in which the pathogen was selectively killed at various times after inoculation, demonstrated that the bacteria are required to be present for gall induction and continued development of the gall for both of the gall-forming Erwinia isolate types. Pathogenicity of the isolated bacteria was tested on 14 conifer species, other than Douglas-fir, including Abies, Chamaecyparis, Pinus and Thuja spp. The typical isolates were weakly pathogenic on Abies, Larix and Picea spp. The atypical isolate was weakly pathogenic on Abies, Chamaecyparis, Larix, Picea and Pinus spp. Due to the limited damage caused on the conifers tested and to their infrequent occurrence, these gall-forming pathogens do not appear to be of economic importance to the forestry industry.
Land and Food Systems, Faculty of
Graduate

The root system is a vital and dynamic part of a plant throughout its lifetime. Its spatial distribution is the consequence of multiple interactions with the surrounding soil medium. In particular, the presence of pathogens in soil may influence the development of the plant, especially the below-ground part, in both its physiology and its structure. Studies of diseased plant roots may take different approaches and investigate disease effects at different levels. In this study, two groups of four potato (Solanum tuberosum L.) plants were grown in middle-sized plastic pots in a greenhouse, and their root systems, together with the soil medium (i.e., sieved and autoclaved homogeneous sand), were submitted to computed tomography (CT) scanning every two weeks until 10 weeks after planting. For the "diseased" group, sand was inoculated with Streptomyces scabies EF-35, the causal agent of potato common scab, at the time of planting. Disease effects on tissue density of roots and below-ground organs, space occupancy and complexity were assessed by analyzing the CT scanning data in the spatio-temporal approach. Fluctuations of tissue density over time were different, on average, between the two groups. They were characterized by an increase of density in Week 2 for the diseased group, reflecting a hardening of tissue, and a delayed decrease relative to the "healthy" group, suggesting a slower transfer of energy from the seed potato to growing roots. Space occupancy, which was studied via volumetric growth rates evaluated from CT scan data, and complexity, which was quantified by the fractal dimension estimated from skeletonized 3-D images constructed from CT scan data, also showed differences in the first part of the experiment. Original analytical procedures based on data transformation and curve fitting in histogram analysis of CT numbers were developed to obtain those results. In conclusion, the new approach presented here, which is based on the advanced processing of CT scanning data collected over time on developing plant root systems and below-ground organs, can be recommended for future phytopathological applications.

Abstract This chapter describes the different diseases and pests that affect yams and various methods for their control. It particularly covers the following aspects: field fungal diseases; postharvest fungal diseases; specific fungal diseases; control of fungal diseases; bacterial diseases; viral diseases; physiological disorders; insect pests; and nematode pests.

Nematodes are the most plentiful animals on earth, commonly found in soil or water, including oceans. Some species of nematodes are parasites of plants and animals. Plant-parasitic nematodes are non-segmented microscopic, eel-like round worms, obligate parasite possess stylets that live in soil causing damage to plants by feeding on roots or plant tissues. Plant-parasitic nematodes feed on roots, either within the root, some nematodes feed leaves. These nematodes cause breakdown of resistance to fungal diseases in fruit crops. Plant-parasitic nematodes living host tissue to feed on to grow and reproduce. Nematode life cycle consists of an egg, 4 pre-adult stages (juveniles) and an adult, life cycle depending on the species and the temperature. Nematodes do not move long distances (less than 6 inches per year). They are usually transported over long distances on machinery, in nursery stock, transplants, seeds, or by animals, moves soil, water and wind. They acquire nutrients from plant tissues by needle-like feeding structure (stylet/spear). Nematodes can be classified into three groups depending on feed on the plants such as ectoparasitic nematodes are always remaining outside the plant root tissues. Migratory endoparasitic nematodes move through root tissues sedentary endoparasitic nematodes penetrate young roots at or near the growing tip. They steal nutrients, disrupt water and mineral transport, and provide excellent sites for secondary pathogens (fungus and bactria) to invade the roots and decay. Several nematode species that cause problems in fruit orchards that are major limiting factors in fruit crop production cause extensive root necrosis resulting in serious economic losses. The root-knot nematode (Meloidogyne spp.), burrowing nematode (Radopholus similis) and citrus nematode (Tylenchulus semipentrans) are the major nematode pests that infect fruit crops. Parasitic nematodes that can damage tree fruit roots. Many kinds of nematodes have been reported in and around the roots of various fruit crops, only few are cause serious damage, including Root-knot nematodes (Meloidogyne spp.), Lesion nematodes (Pratylenchus species), Ring nematodes (Mesocriconema spp) are cigar-shaped that are strictly ectoparasitic, Dagger nematodes (Xiphinema spp) are relatively large ectoparasites that feed near root tips, Sting nematodes (Belonolaimus species) are ectoparasitic, Citrus nematodes (Tylenchulus semipenetrans) are sedentary semi-endoparasites. Nematodes reduce yield without the production of any noticeable above ground symptoms. Typical above ground symptoms of nematode infections stunting, yellowing and wilting. Major nematodes associated in large number of vegetables crops in India such as root-knot nematodes (Meloidogyne spp.), cyst nematodes (Heterodera spp.), lesion nematodes (Pratylenchus sp.), reniform nematodes (Rotylenchulus sp.) lance nematodes (Hoplolaimus spp.), stem and bulb nematode (Ditylenchus spp.) etc. Root-knot nematodes are important pests of vegetables belonging to solanaceous (brinjal, tomato, chili), cucurbitaceous (biter ground, cucumber, pumpkin, bottle gourd) leguminous (cowpea, bean, pea), cruciferous cauliflower, cabbage, broccoli, brussels, sprout), okra and several other root and bulb crops (onion, garlic, lettuce, celery, carrot, radish). Four species (M. incognita, M. javanica, M. arenaria and M. hapla) are more than 95% of the root-knot nematode population worldwide distribution. Stem and Bulb nematode (Ditylenchus spp.) commonly attacks onion, garlic, potato, pea and carrot etc. The nematodes spread from one area to another mainly through infested planting materials, water drains from infested areas into irrigation system, soil that adheres to implements, tyres of motor vehicles and shoes of plantation workers. Management recommendation through bio-pesticides, cultural practices, enrichment of FYM, Neem cake and other organic amendments.

The success of the UN Sustainable Development Goals in reducing hunger and poverty is limited by crop losses. Globally, plant pests and diseases account for 40% yield losses which threatens food and nutrition security, livelihoods of citizenry and erode the resources of local and national economies. Phytophthora diseases are among the most important diseases in sub-Saharan Africa which result in severe socio-economic consequences. Roots and tubers and cash commodity crops are important staples and foreign exchange earner crops in Ghana which are significantly challenged by the incidence and severity of Phytophthora diseases. To ensure food availability, safeguard the local financial ecosystem and protect the environment, innovative and sound management practices are needed and this chapter reviews the different Phytophthora diseases on crops; more specifically with (cocoa and taro as case studies), the consequences and available management options that can be applied to manage the disease situation in Ghana.

Soybean (Glycine max L. Merr) is the most important legume and threaten by diverse pests and diseases. Complex interactions among rhizosphere organisms are found in all agro-ecosystems. Results of these interactions can be positive and/or negative in terms of plant production. Soil nematode community consists of different trophic groups of nematodes. Nematodes are the most abundant soil invertebrates. Several nematode species penetrate soybean roots as parasites, and can cause loss in yields. Arbuscular mycorrhiza fungi are obligate plant symbionts that colonize soybean roots naturally. The aim of the study was to evaluate effects of irrigation and amendments of bioproducts containing beneficial soil microorganisms (ABM) on nematode community and mycorrhizal root colonization in soybean. Field experiments were conducted in soybean in 2013 in Osijek, Croatia. The plots were either rain fed or irrigated to 60-100% field water capacity (FWC). We tested soil amendments and soil + foliar amendments of three commercial products containing beneficial organisms. Average number of nematodes per soil sample varied from 186,67 (soil ABM in non-irrigated plots) to 297,57 (soil+foliar ABM in plots with 60-100% FWC), and there were no significant differences between the treatments. Bacterial feeding nematodes were the most abundant, while plant parasitic genus Pratylenchus was the most abundant among other plant parasitic nematodes. There was no clear influence of any of the treatments on soil nematode community. Amendments of the bioproducts increased mycorrhizal root colonization in rain fed plots, while it decreased the mycorrhizal root colonization when soybeans were irrigated. Irrigation increased mycorrhizal root colonization in plots without amendments of the bioproducts, and mycorrhizal colonization differed significantly between the sampling dates. Further research is needed to determine if irrigation alters the potential of mycorrhiza to colonize the roots.