Show simple item record

dc.contributor.advisorWingfield, M. J.
dc.contributor.advisorCoutinho, T. A.
dc.contributor.advisorWingfield, B. D.
dc.contributor.authorVan Zyl, Leonel Merwe
dc.date.accessioned2017-05-09T06:19:01Z
dc.date.available2017-05-09T06:19:01Z
dc.date.issued1999-05
dc.identifier.urihttp://hdl.handle.net/11660/6192
dc.description.abstractEnglish: English: In chapter one of this thesis, the literature pertaining to the genus Coniothyrium and its importance in plant pathology, is reviewed. Special attention is given to Coniothyrium species associated with Eucalyptus but the focus is on Eucalyptus stem canker pathogen, C. zuluense. Coniothyrium zuluense is an important pathogen in South Africa and has, since its discovery, become widespread throughout plantation areas of KwaZulu-Natal. The current means for reducing the impact of this disease is to plant disease resistant species and clones of Eucalyptus. It is evident from this review that very little information is available pertaining to the biology, reproductive system, or the population structure of C. zuluense. Such information is essential for managing the disease successfully in the future. The strategy currently used to reduce the impact of Coniothyrium canker in plantations is to deploy Eucalyptus species or clones that are resistant to the disease. Considerable success has already been achieved in this regard, but the long-term durability of resistance is of concern. Results of the study represented in chapter two showed that there is considerable variation in colony colour and pathogenicity of a large collection (344) of C. zuluense isolates. Conidial morphology and growth requirements are, however, similar for all isolates tested. The considerable variation in pathogenicity indicates that C. zuluense has been present in South Africa for an extended period of time, or that virulence is changing rapidly due to strong directional selection pressure. Results of the taxonomic and pathogenicity studies in chapter two, suggest that the C. zuluense population is well established. In chapter three, the population diversity of 108 C. zuluense isolates, differing in their pathogenicity to a susceptible Eucalyptus clone, was investigated using Amplified Fragment Length Polymorphism (AFLP) technology. Results indicated that the level of genetic diversity is relatively low, but higher than expected for an asexually reproducing pathogen. Genetic similarity values also indicated a significant population differentiation between different plantation regions (subpopulations), suggesting that gene flow, together with selection, might be responsible for most of the gene diversity. New epidemics would, therefore, not be as a result of the emergence of new aggressive strains, but would rather be due to the introduction of susceptible Eucalyptus species, together with environmental conditions favouring disease development. A Coniothyrium species associated with similar symptoms to those associated with C. zuluense in South Africa was observed on E. camaldulensis in Thailand in 1996. It was previously thought that C. zuluense was restricted to South Africa. In chapter four, I show using morphological and molecular comparisons, as well as pathogenicity studies, that C. zuluense and the Coniothyrium sp. from Thailand are the same organism. This is, thus, the first record of this important Eucalyptus stem canker pathogen, C. zuluense, outside South Africa. Bacteria commonly exude from necrotic cankers on severely infected Eucalyptus clones in plantations. In chapter five, it was shown that bacteria associated with Coniothyrium canker in the field are species of the genus Pantoea. These species were identified based on 16S rDNA sequence data as P. ananatis pv. ananatis and a species closely related to P. stewartii subsp. stewartii. It was also shown that a synergistic interaction between C. zuluense and both Pantoea species exists. Inoculation studies, using both Pantoea species together with C. zuluense isolates, resulted in a significant increase in pathogenicity as opposed to inoculations where the bacterial and fungal isolates were used alone. Future studies should consider the presence or absence of both bacteria species in disease development in Thailand. During plant-pathogen interactions, pathogens are known to produce cell wall degrading enzymes, in particular pectin degrading enzymes. Polygalacturonase (PG) is the first enzyme produced during such interactions and is known to be a determining factor in pathogenicity. Chapter six showed that C. zuluense isolates and both Pantoea species, P. ananatis pv. ananatis and an unknown Pantoea sp., produce PG. Experimental assays show that levels of PG activity for both Pantoea spp. are significantly higher than those obtained for C. zuluense isolates. As PG is the first enzyme produced during disease development it is hypothesised that the two Pantoea species might play a significant role in the development of Coniothyrium canker. Production of PG could also be used as an assay to evaluate pathogenicity in different isolates of C. zuluense. Pathogen-produced cell wall-degrading enzymes play a key role in activating plant defence responses. Most inducible defence responses are the result of transcriptional activation of genes. Various plant resistance (R) genes, as well as pathogenesis-related proteins, such as polygalacturonase inhibiting proteins (PGIPs), have been linked with resistance to various fungal and bacterial pathogens. In chapter seven, a partially sequenced resistance gene from disease resistant E. grandis clone, TAG 5, was shown to be similar to a gene associated with a disease resistance gene in Arabidopsis thaliana. The most exciting aspect of this study was, however, the discovery of a shift in reading frame of this gene for the susceptible Eucalyptus clone, ZG 14. The complete sequence of this gene should provide a more complete view of its importance in disease resistance. Screening for similar interruptions in the open reading frame of various commercially available Eucalyptus clones could significantly speed up breeding programmes aimed at producing improved disease resistant clones.en_ZA
dc.description.abstractAfrikaans: Die literatuur met betrekking tot die belang van die genus Coniothyrium in plant patologie is in hoofstuk 1 in heroonskou geneem. Spesifieke aandag is gegee aan die Eucalyptus stamkankerpatogeen, Coniothyrium zuluense. Uit die oorsig is dit duidelik dat daar 'n tekort aan informasie rakende die basiese biologie van die fungus soos voortplantings meganisme en populasie diversiteit bestaan. Hierdie inligting is van kardinale belang met die oog op die ontwikkeling van siekte beheerprogramme. Die strategie wat tans gebruik word om verspreiding van die siekte te beheer, is deur die seleksie van siekte weerstandbiedende Eucalyptus klone. Bogenoemde praktyk is suksesvol, alhoewel daar kommer bestaan oor die langdurigheid van weerstand in geselekteerde klone. Resultate van hoofstuk twee het getoon dat daar 'n aansienlike variasie in die populasie van C. zuluense is met betrekking tot koloniekleur en patogenisiteit. Spoor morfologie en groei temperatuur voorkeure was egter dieselfde vir al die isolate (344 isolate) bestudeer. Die vlak van variasie in patogenisiteit kan moontlik daarop dui dat C. zuluense al 'n geruime tyd in Suid Afrika voorkom, of dat 'n verandering in virulensie bespoedig word as gevolg van seleksie druk. Resultate van hoofstuk twee dui daarop dat die populasie van C. zuluense in Suid Afrika relatief divers is. In hoofstuk drie is daar, dus, gefokus op die bepaling van die populasie diversiteit van 108 C. zuluensie isolate met behulp van "Amplified Fragment Length Polymorphism". Geselekteerde isolate het verskil ten opsigte van hul patogenisiteit tot 'n vatbare Eucalyptus kloon. Resultate het daarop gedui dat die vlak van genetiese diversiteit relatief laag was, maar hoër as wat verwag is van 'n patogeen wat nie-seksueel voortplant. Genetiese similariteitswaardes het ook aangedui dat betekenisvolle differensiasie tussen plantasie gebiede (sub-populasies) van die patogeen voorkom. Dit is 'n aanduiding dat genetiese vloei, tesame met seleksie, moontlik vir die geen diversiteit verantwoordelik is. Uitbreek van nuwe epidemies sal dus nie veroorsaak word deur nuwe aggressiewe rasse van die patogeen nie, maar eerder deur die aanplanting van vatbare Eucalyptus klone, tesame met gunstige omgewings faktore. Coniothyrium kanker was voorheen net bekend in Suid Afrika. Gedurende 1996, is siekte simtome, soortgelyk aan die van C. zuluense in Suid Afrika, opgemerk op 'n E. . camaldulensis kloon in Thailand. In hoofstuk vier is deur middel van morfologiese-, molekulêre- en patogenisiteits-studies bewys dat die Coniothyrium spesie van Thailand en C. zuluense, dieselfde organisme is. Dit is dus die eerste aanmelding van hierdie gevreesde siekte buite Suid Afrika. Bakterieë word alledaags opgemerk waar dit uit stam kankers van uiters vatbare Eucalyptus klone vloei. Resultate van hoofstuk vyf het getoon dat twee bakterie spesies van die genus Pantoea met Coniothyrium kanker geassosieer is. Identifikasie is gedoen deur die basispaar opeenvolging van die 16S rDNA geen van beide bakterieë te vergelyk met die basispaar opeenvolging van 16S rDNA gene van verwante spesies. Een bakterium is geïdentifiseer as P. ananatis pv. ananatis en die ander spesie as naby verwant aan P. stewartii subsp. stewartii. Uit die resultate was dit ook duidelik dat daar 'n sinergistiese verwantskap tussen C. zuluense en beide Pantoea spesies bestaan. Patogenisiteits-studies het getoon dat 'n betekenisvol greoter letsels geproduseer is wanneer C. zuluense isolate in kombinasie met beide Pantoea spesies in bome geinokuleer is. Plant patogene is bekend vir die produksie van verskeie ensieme om plantselwande af te breek, spesifiek pektien-afbreekende-ensieme. Die pektiese ensiem, polygalacturonase (PG), is bekend as die eerste ensiem wat gedurende plantpatogeen interaksies geproduseer word, en word beskou as 'n bepalende faktor in siekte vorming. Resultate uit hoofstuk ses toon dat C. zuluense en beide Pantoea spesies, P. ananatis pv. ananatis en die onbekende Pantoea spesie, PG kan produseer. Polygalacturonase aktiwiteit vir beide Pantoea spesies was betekenisvol hoër in vergelyking met die van C. zuluense. Dit bleik uit die resultate dat PG produksie van beide Pantoea spesies moontlik 'n noemenswaardige rol kan speel in letsel vorming van Coniothyrium canker. Plantselwand-afbrekende-ensieme speelook 'n noemenswaardige rol in die aktivering van die plant se weerstandsmeganismes. Die aktivering van verskeie PG inhiberings-proteine (PGIPs), is voorheen direk gekoppel aan verhoogde weerstand teen fungus- and bakteriesiektes. In hoofstuk sewe is gevind dat 'n weerstandsgeen wat naby verwant is aan 'n weerstandsgeen in Arabidopsis thetiene. in 'n siektetolerante E. grandis kloon, TAG 5, teenwoordig is. Die E. grandis kloon, ZG 14, wat bekend is vir vatbaarheid vir verskeie bosbou verwante siektes, het egter 'n leesraam verskuiwing in die bogenoemde geen gehad. Dit kan 'n moontlike verduideliking verskaf vir die vatbaarheid van die spesifieke kloon vir siektes. Laasgenoemde resultate kan gebruik word vir die vinnige identifisering van soortgelyke leesraam verskuiwings in klonale materiaal, wat tot die uitskakeling van sulke vatbare klone in die bosbou bedryf kan lei.af
dc.description.sponsorshipNational Research Foundation (NRF)en_ZA
dc.description.sponsorshipSouth African Forestry Industryen_ZA
dc.description.sponsorshipUniversity of the Free State, Department of Microbiology and Biochemistryen_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectEucalyptus -- Diseases and pestsen_ZA
dc.subjectCanker (Plant disease)en_ZA
dc.subjectThesis (Ph.D. (Microbiology and Biochemistry))--University of the Free State, 1999en_ZA
dc.titleFactors associated with coniothyrium canker of Eucalyptus in South Africaen_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


Files in this item

Thumbnail

This item appears in the following Collection(s)

Show simple item record