Nürtingen, FH, Diplomarb., 2004. / Betreuer: Barbara Elers.

Universiẗat, Diss., 2002--Bonn.

Experiments were done to determine pathogenic variability and pathogenic adaptation of Septoria tritici to different wheat cultivars. Fifteen S. tritici isolates from California, Oregon, and Texas were evaluated on seedlings of two sets of geographically diverse wheat cultivars under greenhouse conditions. Significant isolate effects, cultivar effects, and isolate X cultivar interactions were found, though the interaction terms were very small compared to the main effects of isolate and cultivar. All except one isolate were virulent to two sets of cultivars, and the virulence patterns varied among the isolate-cultivar combinations. Variability in virulence among the S. tritici isolates within and between locations also was observed. The isolates were usually more virulent to the cultivars of the same geographic origin than cultivars of other locations, and this demonstrates location-specific adaptation of S. tritici. Four populations of S. tritici, secured from four winter wheat cultivars grown in a field experiment, were evaluated on seedlings of the same wheat cultivars under greenhouse conditions. Significant spore population differences, cultivar differences, and spore population X cultivar interactions were obtained. The interaction term was fairly large compared to the main effect of spore population, and it is likely that the significant interaction was due to increased virulence of S. tritici to its own cultivar of origin. The "own" spore population (inoculation with spore population obtained from the same cultivar) produced significantly larger area under disease progress curve on the cultivar of origin than the "others" (inoculation with spore populations obtained from other cultivars), suggesting cultivar-specific adaptation of S. tritici. Spore populations obtained from the two susceptible cultivars indicated general adaptation to all of the test cultivars, whereas, the spore population secured from the most resistant cultivar showed specific adaptation to its cultivar of origin. Consequences of pathogenic variability, increased virulence, and adaptation of S. tritici to wheat cultivars are discussed. / Graduation date: 1994

No description available.

No description available.

Zugl.: Kaiserslautern, Techn. Univ., Diss., 2009

Zymoseptoria tritici is an ascomycete fungus that causes Septoria tritici leaf blotch disease, which is one of the most devastating diseases of wheat. The lack of molecular tools has withheld functional genomics and consequently has left extensive gaps in the knowledge of the biology of infection by Z. tritici. The current research was conducted to develop molecular tools in order to facilitate forward and reserves genetic screens in Z. tritici. These tools include an optimised genetic manipulation protocol, the Z. tritici strains that provide high frequency targeted genome manipulations, a strategy for gene overexpression and protein tagging, and regulatable promoters for controlled gene expression in Z. tritici. The regulatable promoters served to reveal that the Z. tritici β-(1,3)- glucan synthase (BGS1) gene encoded an essential protein, which regulated cell wall stress tolerance and was therefore, a potential drug target. In addition, these molecular tools revealed a virulence-associated role of the glyoxylate cycle in Z. tritici as inactivation of this pathway impeded pre-penetration morphogenesis, which was restored by exogenous glucose application. This result implied that Z. tritici engaged the glyoxylate cycle to produce energy though gluconeogenesis by channelling the by-products of lipolysis. This significance of the glyoxylate cycle during initiation of the bi-phasic infection cycle suggests that Z. tritici is not a hemibiotroph, but a necrotrophic pathogen with an extended asymptomatic phase of infection. Overall, the molecular tools developed in this study will facilitate large-scale functional genomic analyses to interrogate the biology of infection by Z. tritici. The resulting data will inform the development of durable control strategies to combat Z. tritici outbreaks.

Fusarium head blight (FHB) caused by Fusarium graminearum and Septoria tritici blotch (STB) caused by Septoria tritici are economically important wheat diseases in Ontario. Both reduce yield, FHB is associated with mycotoxin accumulation including deoxynivalenol (DON). Different F. graminearum chemotypes produce either DON/15-acetyldeoxynvialenol (ADON) or DON/3-ADON. The majority (97.5%) of F. graminearum isolates collected from commercial fields across Ontario were 15-ADON chemotype, the remaining were 3-ADON. In inoculated field experiments 3-ADON chemotypes were more aggressive and toxic compared with 15-ADON chemotypes as measured by FHB symptoms and DON content. In inoculated field experiments with a population derived from ‘RCATL33’ and ‘RC Strategy’ soft red winter wheat parents, genetic resistance was more effective than fungicide application at controlling FHB. Field trials with the hard red winter wheat population derived from ‘Maxine’ and ‘FTHP Redeemer’ parents revealed that STB and FHB phenotypic resistance had no negative impact on grain yield in the absence of disease.

Zugl.: Kiel, Univ., Diss., 2007

University, Diss., 2005--Kiel.