Browsing by Author "Du Plessis, Ihan Lambert"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    The diversity and epidemiology of Botryosphaeriaceae species associated with grapevines and woody hosts surrounding vineyards in South Africa
    (Stellenbosch : Stellenbosch University, 2020-12) Du Plessis, Ihan Lambert; Halleen, Francois; Mostert, Lizel; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Botryosphaeriaceae species are reported globally as causal agents of grapevine trunk diseases which translate to yield losses as well as a reduction in the productive lifespan of affected vines. Growers rely on management practises to try and prevent vines from becoming infected. However, despite decades of implementation, current disease management strategies do not fully protect grapevines from becoming infected. This highlights a need for an improved understanding of the epidemiology of these pathogens as well as the development of improved disease management strategies. The aim of this study was to investigate the diversity of Botryosphaeriaceae species occurring on both grapevines as well as other woody hosts within the wine growing regions of the Western Cape Province. In addition, the potential threat that these other hosts pose to the grapevine industry by acting as sources of pathogen inoculum was investigated by characterizing and comparing different populations of the pathogen N. stellenboschiana isolated from both grapevines as well as non-grapevine hosts. The species diversity survey reported 20 different Botryosphaeriaceae species from 38 different host species which were located within 50 m of vineyards. These represented 114 different host/ fungi combinations which were not previously known in South Africa. This survey was dominated by three Botryosphaeriaceae species, Diplodia seriata, Neofusicoccum australe and N. stellenboschiana which constituted 85.1% of all the isolates obtained during this survey. These species are also known grapevine pathogens and were reported from 19, 11 and 24 different host species respectively which highlights the broad host range of these economically important pathogens. The species diversity survey also yielded six new Botryosphaeriaceae species which were formally described and their pathogenicity towards grapevines and olive trees, where relevant, were assessed through field pathogenicity trials. All of the new species were shown to form lesions on grapevine or olive shoots which were comparable to those caused by known Botryosphaeriaceae pathogens, demonstrating the capacity of these species to act as pathogens of these economically important hosts. The population genetics study was carried out based on seven microsatellite markers which were demonstrated to be polymorphic in this study. This study reported that N. stellenboschiana populations from grapevines and other hosts at three different locations in the Western Cape Province were genetically homogenous. This indicates that there are no barriers which prevent the movement of N. stellenboschiana between grapevines and other hosts. These results are disconcerting because they imply that woody hosts surrounding grapevines which are infected with Botryosphaeriaceae grapevine pathogens could be acting as disease reservoirs and sources of pathogen inoculum which threaten vineyards. To conclude, this study furthered our understanding of the diversity of Botryosphaeriaceae species occurring in woody hosts that commonly surround vineyards in the Western Cape Province of South Africa and described six new species. Furthermore, this study has contributed to our understanding of the epidemiology of these pathogens by demonstrating that the alternative hosts of Botryosphaeriaceae grapevine trunk disease pathogens represent a threat to grapevines by acting as sources of pathogen inoculum. This helps to lay the groundwork for future studies to address this threat by developing improved pathogen management strategies.
  • Thumbnail Image
    Item
    The diversity of Trichoderma spp. in South Africa
    (Stellenbosch : Stellenbosch University, 2015-03) Du Plessis, Ihan Lambert; Jacobs, Karin; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH SUMMARY: The genus Trichoderma includes economically important species that are routinely applied in fields such as agriculture and biotechnology. Species like T. harzianum and T. asperellum are commercially applied as biological control agents, whereas other species such as T. reesei, are used in the production of industrial enzymes. Few studies have investigated the diversity of this important genus in South Africa. The aim of this study was to investigate the diversity of Trichoderma species in South Africa by isolating and identifying strains from soils collected in different parts of the country. In addition, strains were screened for their ability to antagonize plant pathogens in vitro, to assess their potential for possible future development as biocontrol agents. Chapter One explores the history of Trichoderma and outlines the various criteria that are used to describe and identify species within the genus. The ecology of Trichoderma species, and the manners in which they interact with other organisms, are also discussed. Next, the various impacts of Trichoderma species on industry, agriculture and healthcare were outlined to highlight the importance of these organisms. The final section of the chapter reviews the research that has investigated Trichoderma strains from South Africa in the past. A taxonomic inventory of South African Trichoderma species is presented in Chapter Two. In total, 161 different Trichoderma strains were isolated from 173 sample sites. These were identified based on their morphological characteristics as well as through phylogenetic analyses using ITS and ef1α sequence data. A total of 18 different species were isolated, 14 of which could be identified and six of which are first reports. Four new Trichoderma species were discovered during this study. Two of these species belong to the T. longibrachiatum clade and are represented by multiple strains. These species were described in Chapter Three as T. terrigenum prov. nom. and T. vagum prov. nom. The remaining two species were each represented by a single strain and were described in Chapter Four as T. restrictum prov. nom. and T. undulatum prov. nom. Chapter Five investigates the ability of South African Trichoderma strains to antagonize the growth of selected plant pathogens in vitro. The antagonistic activity of the Trichoderma strains were quantified based on their ability to produce volatile and non-volatile antifungal compounds that could inhibit the growth of plant pathogens. The performance of the strains were compared to those of two commercial biocontrol strains that served as positive controls. Several of the South African Trichoderma strains matched or outperformed commercial biocontrol strains in terms of their ability to antagonise the growth of the plant pathogens and therefore they show potential for possible future development as biocontrol agents.