Thesis (PhD (Agric)) -- Stellenbosch University, 2003. / ENGLISH ABSTRACT: Stripe (yellow) rust of wheat, caused by Puccinia striiformis f.sp. tritici, was first detected as a single introduction into South Africa in 1996. Two additional pathotypes have since been identified. Control of the disease may be achieved by use of genetic adult plant resistance (APR) as is present in the local cultivar 'Kariega'. The aim of this project was to understand the genetic basis of the APR in 'Kariega' to facilitate breeding of new varieties with genetic resistance to stripe rust. A partial linkage map of a 'Kariega X Avocet S' doubled haploid population covering all 21 wheat chromosomes was generated using 208 DNA markers, viz, 62 SSR, 133 AFLP, 3 RGA and 10 SRAP markers, and 4 alternative loci. The different marker techniques detected varying polymorphism, viz, overall SSR: 46%, AFLP: 7%, SRAP: 6% and RGA: 9%, and the markers produced low levels of missing data (4%) and segregation distortion (5%). A significant feature of the linkage map was the low polymorphism found in the D genome, viz, 19% of all mapped DNA markers, 11% of all AFLP markers and 30% of the total genome map distance. A region exhibiting significant segregation distortion was mapped to chromosome 4A and a seedling resistance gene for stem rust (Puccinia graminis f.sp . tritici), Sr26, mapped to chromosome 6A close to three SSR markers. The leaf tip necrosis gene, Ltn, which was also segregating in the population, mapped to chromosome 7D. Protocols for SRAP and RGA were optimised, and SRAP marker use in wheat genetic linkage studies is reported for the first time. The linkage map was used together with growth chamber and replicated field disease scores for QTL mapping. Chromosomes showing statistically significant QTL effects were then targeted with supplementary SSR markers for higher resolution mapping. The quality of disease resistance phenotypic data was confirmed by correlation analysis between the different scorers for reaction type (0.799±0.023) and for transformed percentage leaf area infected (0.942±0.007). Major QTL were consistently identified on chromosome 7D (explaining some 25-48% of the variation) and on chromosome 2B (21-46%) using transformed percentage leaf area infected and transformed reaction type scores (early and final) with interval mapping and modified interval mapping techniques. Both chromosomal regions have previously been identified in other studies and the 7D QTL is thought likely to be the previously mapped APR gene Yr 18. Minor QTL were identified on chromosomes lA and 4A with the QTL on 4A being more prominent at the early field scoring for both score types. A QTL evidently originating from 'Avocet S' was detected under growth chamber conditions but was not detected in the field, suggesting genotype-environment interaction and highlighting the need for modifications of growth chamber conditions to better simulate conditions in the field. The genetic basis of the APR to stripe rust exhibited by 'Kariega' was established by mapping of QTL controlling this trait. The linkage map constructed will be a valuable resource for future genetic studies and provides a facility for mapping other polymorphic traits in the parents of this population with a considerable saving in costs. / AFRIKAANSE OPSOMMING: Streep of geelroes van koring word veroorsaak deur Puccinia striiformis f. sp tritici, en is die eerste keer in 1996 in Suid-Afrika na introduksie van 'n enkele patotipe waargeneem. Twee verdere patotipes is sedertdien in Suid-Afrika gei"dentifiseer. Beheer van die siekte word veral moontlik gemaak deur die gebruik van genetiese volwasseplantweerstand soos gei"dentifiseer in die plaaslike kultivar 'Kariega'. Die doel van hierdie studie was om die genetiese grondslag van die streeproesweerstand te ontrafel ten einde die teling van nuwe bestande kultivars moontlik te maak. 'n Verdubbelde haplo1ede populasie uit die kruising 'Kariega X Avocet S' is aangewend om 'n gedeeltelike koppelingskaart vir die volle stel van 21 koring chromosome saam te stel. Die kaart het uit 208 DNA merkers, nl., 62 SSR, 133 AFLP, 3 RGA, 10 SRAP merkers en 4 ander lokusse bestaan. Totale polimorfisme wat deur die verskillende merkersisteme opgespoor is, was as volg: SSR: 46%, RGA: 9%, AFLP: 7% en SRAP: 6%. Die mate van ontbrekende data was gering (4%) asook die mate van segregasie distorsie (5%) van 'n enkele geval wat op chromosoom 4A gekarteer is. 'n Prominente kenmerk van die koppelingskaart is die relatiewe gebrek aan polimorfiese merkers op die D-genoom, nl., slegs 19% van alle DNA merkers en 11% van alle AFLP merkers wat slegs 30% van die totale genoom kaartafstand bestaan het. Die stamroes (Puccinia graminis f. sp. tritici) saailingweerstandsgeen, Sr26, karteer op chromosoom 6A naby drie SSR merkers. Die geen vir blaartipnekrose, Ltn, karteer op chromosoom 7D. Protokolle vir SRAP en RGA merkers is ge-optimiseer en gebruik van SRAP merkers in koppelings-analise word vir die eerste keer in koring gerapporteer. Die koppelingskaart is in kombinasie met groeikamerdata en gerepliseerde veldproefdata gebruik om die gene (QTL) vir volwasseplant streeproesweerstand te karteer. Chromosome met statisties betekenisvolle QTL is met aanvullende SSR merkers geteiken om die resolusie van kartering verder te verhoog. Die kwaliteit van fenotipiese data, soos in die proewe aangeteken, is bevestig deur korrelasies te bereken tussen lesings geneem deur onafhanklike plantpataloe (0.799 ± 0.023 vir reaksietipe en 0.942 ± 0.007 vir getransformeerde persentasie blaaroppervlakte besmet). Hoofeffek QTL vir die twee maatstawwe van weerstand is deur middel van die metodes van interval QTL kartering en gemodifiseerde interval QTL kartering konsekwent op chromosome 7D (25-48% van variasie verklaar) en 2B (21-46% van variasie verklaar) ge"identifiseer. In vorige studies is aangetoon dat beide chromosome 7D en 2B QTL vir volwasseplant streeproesweerstand dra. Die 7D QTL is waarskynlik die weerstandsgeen, Yr 18. QTL met klein effekte op weerstand is op chromosome lA en 4A ge"identifiseer. Die effek van laasgenoemde geen was meer prominent in die velddata in die vroee datum van weerstandsbeoordeling. Een QTL, afkomstig van 'Avocet S', is slegs onder groeikamertoestande identifiseerbaar. Dit dui op moontlike genotipe-omgewing wisselwerking en beklemtoon die noodsaaklikheid om aanpassings te maak in groeikamertoestande vir beter simulasie van veldproeftoestande. Die genetiese grondslag van volwasseplantweerstand teen streeproes in die kultivar 'Kariega' is deur QTL kartering bepaal. Die 'Kariega X Avocet S' koppelingskaart kan as 'n waardevolle basis dien vir toekomstige genetiese ontledings van ander polimorfiese kenmerke in die populasie.

Bibliography: leaves 245-271 / xiv, 271 leaves, [47] leaves of plates : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Physiology, 1985

The aim of this study was to analyse testcross-material that was generated during a homoeologous pairing-induction experiment. Absence of the homoeologous pairing suppressor gene, Ph1, was employed to induce meiotic pairing between the Lr59 translocation (Aegilops peregrina) and 1AL of normal wheat. The study aimed to characterize the test-cross plants derived from this experiment and to identify recombinants which retained the least amount of species chromatin but which still contained the Lr59 gene. The test-cross F1 population, 07M5 (total 635 plants), was screened for Lr59 resistance by inoculating seedlings with the leaf rust pathotype, UVPrt8. The 168 resistant plants were characterized with molecular markers in order to identify recombinants. The data were used to construct a physical map which showed the relative sizes of the recombinants and which could be used to identify those recombinants which contained the least amount of residual species chromatin. Microsatellite (Xcfa2219, Xbarc83 and Xgwm164) and SCAR (S15T3) analysis was used for the initial identification of recombinants. The results showed that 152 of the 168 resistant plants were recombinants for the four loci; that eight of the remaining 16 plants represented non-recombinant, wild species-types and that the last eight plants represented the wheat parental-types which were resistant (and thus, also recombinants). This extremely high recombination frequency can largely be attributed to strong segregation distortion that was evident in the cross. It is also possible that the translocation segment could derive from the S genome rather than the U genome of Ae. peregrina. The S genome is closer related to the wheat genomes than the U genome and may be more prone to recombination. With the use of the microsatellite and SCAR data, a physical map was constructed which showed the relative location of the Lr59 gene on the translocation. It appeared that the eight shortest recombinants retained terminal species chromatin. In an attempt to characterize the eight recombinants, additional marker loci had to be identified within that region. RAPD, iv AFLP and DArT markers were investigated for this purpose. RAPD analyses did not produce any useful markers. AFLP and DArT analyses did identify useful markers with which the eight recombinants could be screened. The data showed which recombinants probably retained the least amount of species chromatin. Seeing that AFLP and DArT markers are anonymous and that the distances between marker loci are unknown, it is not possible to say which recombinant is the shortest and consequently it will be nessecary to also evaluate the group of eight recombinants agronomically in order to identify the most useful ones. The results showed that multiple cross-overs apparently occured on both sides of Lr59. Multiple cross-overs are higly unlikely in material of this nature, therefore it was speculated that the observation resulted from incomplete synteny between the telomeric areas of the translocation and 1AL. A structural difference between the two chromosome regions might have given rise to abnormal meiotic pairing structures and thus unexpected gamete genotypes. Each of the eight recombinants did express one or more of the Ae. peregrina derived AFLP loci which can in future be verified for use as a marker for marker assisted selection. The study succeeded in identifying a number of potentially useful recombinants which contain the Lr59 resistance. It would, however, be risky to select only one of the shortest recombinants for further development on the basis of the present knowledge as some recombinants may contain genetic abnormalities which resulted from reduced synteny in the Lr59 region. It would therefore be wise to further evaluate all eight recombinants before the best one is selected for agronomic use.

M.Sc. (Botany) / Wheat is the second most important grain crop produced in South Africa. It is mostly used for human consumption (e.g. biscuits, rusks, breakfast cereals, and bread) with the remainder being used as seed and animal feed. Wheat is also used for production of alcohol for ethanol, absorbing agents for adhesives, disposable diapers and industrial uses as starch on coatings (Department of Agriculture, Forestry and Fisheries, 2011). The leading wheat producing areas in South Africa since 1994 are the Western Cape (38 %), Free State (26 %) and Northern Cape (17 %) (Department of Agriculture, Forestry and Fisheries, 2011). There are two main classes of cultivated wheat, these are durum wheat (Triticum durum) that contributes 5 % and common or bread wheat (Triticum aestivum L.), which contribute 95 % of the world wheat production (Kiplagat, 2005). One of the major threats to wheat production in South Africa and other countries is the Russian wheat aphid (RWA), (Kurdjumov), (Diuraphis noxia, Hemiptera: Aphididae) (Brooks et al., 1994). In South Africa, the Russian wheat aphid was reported as a pest of wheat in 1978 in the Eastern Free State (Walters, 1980). In the beginning of the 1979 season, it was detected only in the Eastern Free State, but quickly spread to the Western Free State and parts of Lesotho. Infestations were also isolated in some areas of KwaZulu-Natal, North West and Gauteng Province (Walters et al., 1980). Aphids are soft bodied insects and are the most economically important phloem feeders impacting on plants (Dixon, 1985; Klingler et al., 2009). Aphids damage plants in four ways. Firstly, they ingest vital plant metabolites including large volumes of translocated sugars from the phloem sap, diverting energy from the plant and reducing yield. Secondly, they secrete saliva into the plant tissues while probing the layers of leaf to find the phloem, in some instances the secreted saliva is thought to be phytotoxic (Dedryver et al., 2010). The physical damage done to the leaf along with the toxic attributes of the saliva leads to localized necrosis in some aphid plant interactions (Klingler et al., 2009). Thirdly, aphids act as virus vectors and they can be transmitted in a non-circulative or circulative manner (Chen et al., 2012).

Fusarium graminearum est un champignon pathogène des plantes, responsable de la fusariose de l'épi (plus connue sous le nom de Fusarium Head Blight : FHB) sur céréales, notamment sur le blé et le maïs. En interaction avec la plante, le champignon produit des mycotoxines, parmi lesquellse le déoxynivalénol (DON), dont la finalité pour le champignon producteur est méconnue mais qui sont toxiques pour les humains et les animaux. Ainsi la qualité des grains contribue fortement aux pertes de rendement observées et les résidus contaminés restent au champ. Une première revue bibliographique (Leplat et al 2012) a mis en évidence l'importance des résidus de culture (habitat écologique) pour la survie saprophyte du champignon, pour sa reproduction sexuée et pour l'établissement de l'inoculum primaire susceptible d'infecter la prochaine culture. Une seconde revue bibliographique a souligné les lacunes en ce qui concerne le rôle que les mycotoxines pourraient jouer dans la survie de F. graminearum dans un cet habitat. L'objectif principal de cette thèse était donc de vérifier si la présence de mycotoxines dans les résidus de récolte donne un avantage compétitif à F. graminearum vis-à-vis des composantes biotiques du sol et des résidus et notamment les champignons, les bactéries, les protozoaires, les nématodes et les vers de terre. L'impact du DON sur ces différentes communautés a été évalué dans des résidus de maïs et de blé, au champ et en microcosmes, en condition de labour et de travail superficiel du sol. Le développement de la maladie et ses conséquences sur le rendement ont été observés dans l'expérience de terrain à l'Unité Expérimentale de l'INRA de Dijon.Au cours de cette étude, la survie et les dynamiques de développement de la souche modèle d'étude F. graminearum MIAE00376 et des communautés fongiques et bactériennes ont été mesurées en utilisant la réaction de polymérisation en chaîne en temps réel (Q-PCR) ainsi que par comptage sur boîtes. Dans le même temps, l'évolution des structures des communautés microbiennes a été déterminée par analyse du polymorphisme de longueur des fragments de restriction terminaux (T-RFLP). Les nématodes et les vers de terre ont été quantifiés par extraction et observations à l'œil ou a la loupe binoculaire. Le DON introduit dans le sol et les résidus a été extrait et quantifié au cours du temps par chromatographie liquide haute performance (CLHP). Des dynamiques de population de la souche MIAE00376 associée à différents microorganismes isolés de paille en décomposition et sélectionnés pour leur résistance au DON, à des bactéries fixatrice d'azote et à des Fusarium sp. appartenant au complexe fongique du FHB ont été mesurées en microcosmes de paille en présence ou non de DONLes résultats suggèrent que le DON dans les résidus de culture a une incidence sur les composantes biotiques du sol, mais l'impact dépend des communautés et de la localisation des résidus (en surface ou incorporés dans le sol). La biomasse moléculaire montre que les densités bactériennes et fongiques ont été significativement affectées par la présence de DON. La présence de DON a joué un rôle significatif sur la structure des communautés bactériennes et protozoaires, plus faible sur les communautés fongiques et nul sur les nématodes voire positif sur les vers de terre.Il est conclu que le DON est rapidement inaccessible en profondeur et un peu moins rapidement en surface (immobilisation ou dégradation), qu'il ne confère pas d'avantage compétitif au champignon producteur et que la gestion de l'habitat privilégié que constituent les résidus de culture pour F. graminearum peut être envisagée par le travail du sol en favorisant la décomposition rapide des résidus, par le labour ou l'utilisation d'organismes décomposeurs indigènes ou introduits. / Fusarium graminearum is a plant pathogenic fungus, causing devastating disease “Fusarium head blight” (FHB) in cereals including wheat and maize. It also contaminates the grains with mycotoxins including deoxynivalenol (DON) which are toxic to human and animals. This disease has resulted in the serious losses in grain yield and quality. We established through a first bibliographic review that during off season fungus survives saprophytically on the crop residues (ecological habitat) and serves as primary inoculum for the next season crop. However, we noticed also that the literature was poor about the role mycotoxins could play in the establishment of F. graminearum in such a habitat. The main aim of this thesis was therefore to test whether the presence of mycotoxins in the crop residues gives an advantage to F. graminearum to survive and develop a primary inoculum in the presence of the whole soil biota including fungi, bacteria, protozoa, nematodes and earthworms. We studied the impact of DON on the soil communities in the field as well as in microcosms, in wheat as well as in maize residues under tillage and no-tillage conditions. The disease development and the yield were noted in the field experiment. Some DON resistant active fungal decomposers and nitrogen fixing bacteria were picked and the dynamics of F. graminearum was observed by accelerating decomposition of crop residue in their presence, in the presence or absence of DON.During this study, the dynamic and survival of F. graminearum and total fungal and bacterial communities were examined by using quantitative real time polymerase chain reaction (qPCR) as well as by plate counting. At the same time, the structures of microbial communities were determined by using terminal restriction fragment length polymorphism analysis (T-RFLP). The DON resistance of isolated fungal decomposers and nitrogen fixers was tested by using minimal inhibitory concentration test (MIC). Nematodes and earthworms were quantified through binocular observations. The fate of DON was determined by quantifying the mycotoxin by high performance liquid chromatography (HPLC).The results suggested that DON in crop residues showed an impact on the biotic components of the soil but the impact depended on the communities and on the location of the residues (on surface or incorporated in the soil). The molecular biomass shows that the fungal and bacterial densities were significantly affected by the presence of DON. The presence of DON played significant role on the structure of bacterial and protozoan community while the nematodes and fungal communities remained unaffected. MIC results showed that the susceptibility of some competitive fungal strains towards DON was dependent on the dose of mycotoxin. The earthworms (Lumbricus terrestris) were not affected by the presence of mycotoxin. The degradation of DON in the residues was dependent on the time, the location of residues and the soil biota. The quantification of F. graminearum suggested that the presence of DON gave no advantage in the survival and development of primary inoculum during the decomposition of crop residues in the soil. We conclude that fungal decomposers can be selected on their enzymatic potential towards organic matter more than on the DON resistance to increase the degradation of the straw left at the surface and limit the subsequent development of F. graminearum.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Agric) Plant Pathology)--University of Pretoria, 2003. / Microbiology and Plant Pathology / unrestricted

Thesis (MScAgric)--Stellenbosch University, 1998. / ENGLISH ABSTRACT: Eyespot is an important disease of spring wheat (Triticum aestivum L.). Four species of Ramulispora are associated with this disease, of which Tapesia yallundae and T. acuformis. are common. This thesis investigates the broader subjects of genetic variability, reproductive dynamics and fungicide resistance in Tapesia yallundae. Each of the chapters treats specific but related topics. T. yallundae, which is the only species thus far reported from South Africa, has been associated with yield losses of up to 50%. To enable the implementation of more accurate and effective control measures, understanding the dynamics of reproduction and the genetics of the pathogen is of utmost importance. Of the many plant disease control measures such as cultural practices, sanitation, biological control, etc., fungicide application is the most commonly resorted to measure in eyespot control. This thesis investigates the broader subjects of genetic variability, reproductive dynamics and fungicide resistance of Tapesia yallzll7dae. Fungicide application, however, is not without problems. The pathogen can build up resistance to fungicides. The most commonly used fungicides in eyespot control include the benzimidazole carbendazim, triazoles such as flusilazole, tebuconazole, propiconazole, bromuconazole, flutriafol, fenbuconazole, triademinol, and the imidazole, prochloraz. Cases of resistance to the groups listed above have been reported. Frequent monitoring for resistance is thus crucial to prevent wastage of fungicide and unnecessary impregnantation of the environment with potentially ineffective chemicals. In chapter 2 of this thesis 300 isolates of T. yallundae from 15 fields were evaluated for resistance against carbendazim, flusilazole, tebuconazole, propiconazole, bromuconazole, flutriafol and fenbuconazole. These results indicated that to some triazoles, such as fenbuconazole, a high level of resistance was already present in field populations. In a sexually reproducing fungus such as T. yallundae, knowledge pertaining to its ability to pass resistance factors to offspring is equally important. Mating studies were, therefore, also conducted with parental strains that showed signs of triazole resistance. Three generations were subsequently tested for resistance to five triazoles, namely flusilazole, tebuconazole, propiconazole, bromuconazole and flutriafol. Results of this study showed variable sensitivity in progeny, which indicated quantitative inheritance of resistance to triazoles. Although the sexual stage has not yet been observed in the field in South Africa, this knowledge lays the foundation for the long-term understanding of the population dynamics of the fungus. The ability of a heterothallic ascomycete population to reproduce sexually is dependent on the availability of its two mating types, MATI-I and MATI-2, their distribution, and female fertility amongst other factors. In the UK. the teleomorph is commonly observed in the field, which is in contrast to the situation in South Africa, where it has only been induced in the laboratory. A comparative study between the South African and the UK. populations was therefore undertaken. Isolates representative of the two populations were mated with tester strains as both sperm recipients and as sperm donors. This allowed the percentage of hermaphrodites to be determined. No difference in terms of female fertility was observed between the South African and the UK. populations, with both populations showing low effective population numbers. These data suggested, therefore, that the teleomorph would also occur more frequently in South Africa if the climate was more indusive to its development. The overall results of this study indicated that eyes pot could still be controlled by means of fungicide application in South Africa. Although a shift in sensitivity was observed towards fenbuconazole and flusilazole, no resistance was detected towards carbendazim. The latter might be due to the absen<.:eof the sexual stage in the field, coupled by the monocyclic nature of the pathogen and sensible fungicide regimes. The absence of T. acujormis makes the disease situation less complicated in terms of fungicide application and management. Continuous surveys will have to be conducted, however, to monitor this situation in future. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die genetiese variasie, reproduksie dinamika en fungisied weerstand in Tapesia yallundae. Elke hoofstuk handel oor spesifieke maar verwante onderwerpe. Oogvlek is 'n belangrike siekte van lentekoring (Triticum aestivum L.). Vier spesies van Ramulispora word geassosieer met die siekte, waarvan Tapesia yallundae en T. acuformis mees algemeen voorkom. T. yallundae, wat tans die enigste spesie is wat in Suid-Afrika aangeteken is, het al verliese van tot 50% veroorsaak. Om meer akkurate en effektiewe beheermaatreels te implementeer, is dit noodsaaklik om die oorlewingsdinamika van die patogeen te verstaan. Van al die siektebeheermaatreels soos kulturele praktyke, sanitasie, biologiese beheer ens., bly fungisiedbehandeling die mees algemene maatreel vir die beheer van oogvlek. Fungisiedtoediening het egter ook verskeie probleme. Die patogeen kan weerstand opbou teen die fungisied. Die mees algemene fungisiedes wat vir oogvlekbeheer aangewend word sluit onder meer die benzimidasool karbendazim in, triasole soos flusilasool, tebukonasool, propikonasool, bromukonasool, flutriafol, fenbukonasool, triadimenol, en die imidasool, prochloraz. Weerstand is egter reeds teen hierdie middels bekend. Gedurige monitering vir weerstand is dus krities om die vermorsing van fungisied en besoedeling van die omgewing met oneffektiewe middels te beperk. In hoofstuk 2 van hierdie manuskrip word 300 isolate van T. yallundae van 15 lande geevalueer vir weerstand teenoor karbendazim, flusilasool, tebukonasool, propikonasool, bromukonasool, flutriafol en fenbukonasool. Resultate dui daarop dat teen sommige van hierdie triasole, soos bv. fenbukonasool, daar reeds 'n hoe vlak van weerstand teenwoordig was in veldpopulasies. In 'n seksueel reproduserende fungus soos T. yalluJ1dae, is dit noodsaaklik om te bepaal wat sy vermoe is om weerstandbiedenheid aan die nageslag oor te dra. Om die rede is paringstudies ook op ouers wat tekens van weerstand teenoor triasole getoon het uitgevoer. Drie generasies was gevolglik getoets vir weerstand teenoor vyf triasole, naamlik flusilasool, tebuconasool, propikonasool, brumukonasool en flutriafol. Resultate van die studie het 'n variasie in sensitiwiteit van die nageslag getoon, wat op 'n kwantitatiewe oorerwing van weerstand teen £riasole dui. Alhoewel die teleomorf nog nie in lande in Suid-Afrika opgemerk is nie, Ie hierdie kennis die fondament vir die langtermyn vertolking van die populasie dinamika van hierdie fungus. Die vermoe van 'n heterotalliese askomiseet populasie om seksueel voort te plant is afhanklik van die beskikbaarheid van sy twee paringstipes, MATI-I en MATl-2, hul verpreiding, vroulike vrugbaarheid en ander faktore. Alhoewel die teleomorf algemeen in lande in die Verenigde Koninkryk opgemerk word, is dit in kontras met die situasie in Suid-Afrika, waar hierdie stadium nog slegs in die laboratorium gelnduseer kon word. 'n Studie is dus onderneem om die Suid-Afrikaanse en V.K. populasies met mekaar te vergelyk. Isolate van die twee populasies is dus gepaar met paringsisolate as beide sperm ontvangers en sperm donors. Hierdie prosedure het dit moontlik gemaak om die persentasie hermafrodiete te bepaal. Geen verskille in vroulike fertiliteit is tussen die Suid-Afrikaanse en V.K. populasies bespeur nie, en beide populasies het ook 'n lae effektiewe populasie getal getoon. Hierdie data het dus voorgestel dat die teleomorf ook meer algemeen in Suid-Afrika sou voorkom as die klimaat meer geskik was vir teleomorf vormmg. Die resultate van hierdie studie het tot die slotsom gelei dat oogvlek steeds deur fungisiedbehandeling in Suid-Afrika beheer kan word. Alhoewel daar 'n merkbare verskuiwing in sensitiwiteit teenoor fenbukonasool en flusilasool was, was geen weerstand teenoor karbendazim waargeneem nie. Laasgenoemde kan dalk toegeskryf word aan die afwesigheid van die teleomorf in die veld, gekombineer met die monosikliese natuur van die patogeen en gebruik van alternerende fungisiedes. Die afwesigheid van T. acuformis maak die plaaslike siektetoestand minder gekompliseerd in terme van fungisied aanwending en bestuur. Voortdurende opnames sal egter uitgevoer moet word om hierdie situasie ook in die toekoms te monitor.

Bibliography: leaves 307-329. This study concludes that in soils in South Australia where root-rotting fungi and P. neglectus exist together, root disease of wheat is caused by their combined effect. Evidence suggests that P. neglectus not only contributes to this interaction through mechanical wounding of roots, but also causes biochemical and physiological changes in plants, making them more prone to fungal infection.

Bibliography: leaves 207-220. Pseudomonas corrigata strain 2140 (Pc2140), isolated from wheat field soil in Australia, antagonises the take-all fungus, Gaeumannomyces graminis var. tritici (Ggt) in vitro and significantly reduces take-all symptoms on wheat in pot trials. This study investigates the mechanisms by which the biocontrol agent reduces the disease symptoms. Biochemical analysis of metabolites of P. corrugata 2140 reveal a number of compounds potentially antagonistic to Ggt and which may play a role in disease control. These include water-soluble antibiotics, siderophores, proteases, peptides and volatiles including hydrogen cyanide.

Bibliography: leaves 307-329. / xvi, 329 leaves, [21] leaves of plates : ill. (chiefly col.), map ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study concludes that in soils in South Australia where root-rotting fungi and P. neglectus exist together, root disease of wheat is caused by their combined effect. Evidence suggests that P. neglectus not only contributes to this interaction through mechanical wounding of roots, but also causes biochemical and physiological changes in plants, making them more prone to fungal infection. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996