The diversity of Trichoderma spp. in South Africa

Du Plessis, Ihan Lambert (2015-03)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

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.

AFRIKAANS OPSOMMING: Die genus Trichoderma bevat ekonomiese belangrike spesies wat toegepas word in landbou en biotegnologie. Spesies soos T. harzianum en T. asperellum word kommersieel toegedien as biologiese beheer middels waar ander spesies, soos T. reesei, gebruik kan word vir die vervaardiging van industriële ensieme. Tot op hede was daar slegs ‘n paar studies wat hierdie belangrike groep swamme in Suid Afrika ondersoek het. Die doel van hierdie studie was om die diversiteit van Trichoderma spesies in Suid Afrika te bestudeer deur stamme te isoleer en identifiseer vanuit grond monsters wat geneem was regoor die land. Die geïsoleerde stamme was ook ondersoek vir die vermoë om sekere plant patogene se groei te onderdruk onder laboratorium omstandighede. Hierdie was gedoen om hulle potensiaal te meet vir moontlike verdere kommersiële ontwikkeling as biologiese beheer agente. Hoofstuk Een ondersoek die geskiedenis van Trichoderma en beskryf die verskillende kriteria waarvolgens spesies gekarakteriseer word. Die ekologie van Trichoderma spesies, en die wyse waardeur hulle ander organismes beïnvloed, word ook bespreek. Die verskeie impakte van Trichoderma spesies op die industrie, landbou en gesondheidsorg, word volgende bespreek om die belangrikheid van hierdie groep swamme te beklemtoon. Ten slotte van hierdie hoofstuk word daar ‘n oorsig gegee van navorsing wat Suid Afrikaanse Trichoderma stamme ondersoek het in die verlede. Die verskillende Trichoderma spesies wat geïdentifiseer was in Suid Afrika tydens hierdie studie word in Hoofstuk Twee gelys en bespreek. In totaal was 161 verskillende Trichoderma stamme geïsoleer vanaf 173 grond monsters. Hierdie stamme was geïdentifiseer volgens hulle morfologiese eienskappe sowel as ITS en ef1α DNA basispaaropeenvolging data. In totaal was 18 verskillende Trichoderma spesies geïsoleer tydens hierdie studie, 14 van hierdie spesies was geïdentifiseer en ses van die spesies was vir die eerste keer in Suid Afrika aangeteken. Vier nuwe Trichoderma spesies was ontdek tydens hierdie studie. Twee van hierdie spesies behoort aan die T. longibrachiatum groep en word verteenwoordig deur meer as een stam. Hierdie spesies was beskryf in Hoofstuk Drie as T. vagum prov. nom. en T. terrigenum prov. nom. Die ander twee nuwe spesies word elk verteenwoordig deur ʼn enkele stam en was beskryf in Hoofstuk Vier as T. restrictum prov. nom. and T. undulatum prov. nom. In hoofstuk Fyf word die vermoë van Suid Afrikaanse Trichoderma stamme ondersoek om die groei van geselekteerde plant patogene te onderdruk onder laboratorium omstandighede. Die antagonistiese aktiwiteit van die Trichoderma stamme was gekwantifiseer gebaseer op die mate waarvolgens hulle afgeskeide vlugtige en nie-vlugtige antifungale stowwe die groei van die plant patogene onderdruk het. Die anti-fungus aktiwiteit van die stamme was vergelyk met twee kommersiële biobeheer stamme wat gedien het as positiewe kontrole. Verskeie Trichoderma stamme het die kontrole stamme oortref in term van hulle vermoë om die groei van die plant patogene te onderdruk. Hierdie spesies toon potensiaal vir moontlike verdere ontwikkeling as biologiese beheer agente.

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