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Title: Parasexual analysis of fungicide sensitivity and pathogenicity in the eyespot fungus Pseudocercosporella herpotrichoides
Author: McNaughton, Janice Elizabeth
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1996
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The two major pathotypes (W & R) of the cereal eyespot fungus, Pseudocercosporella herpotrichoides, show variation of major agronomic importance, specifically in sensitivity to fungicides and in differences in host species specificity. This thesis describes the genetic analysis of these characters using the parasexual cycle to generate recombinant progeny between W and R pathotypes. Interspecific hybrid progeny from a parasexual cross between P. herpotrichoides and P. anguioides were included in the analysis. Marker differences present in the parental isolates including auxotrophic requirements, isozyme banding patterns, sensitivity towards benzimidazole fungicides and spore length have been used as proof of recombination in the parasexual progeny, and to characterise the pattern of genetic segregation in the crosses. Analysis of fungicide sensitivity focused on the ergosterol biosynthesis inhibitors (EBI), where it is found that W-types are significantly more sensitive to the majority of the demethylation inhibiting (DMI) fungicides than are the R-types. Determination of sensitivity of progeny to EBI fungicides revealed the presence of 'major' and 'minor' gene(s) controlling the expression of fungicide resistance. Major gene segregation resulting in a substantial difference in sensitivity to triadimenol, was found to occur prior to exposure of the diploid fusion products to haploidizing agents with the result that progeny generated from any one fusion product were sensitive or resistant to triadimenol. Segregation of additional minor genes occurred following exposure to haploidizing agents and these modified the level of resistance expression within the progeny. These analyses provided the first genetic evidence for cross-resistance to these fungicides in this fungus. Cross-resistance relationships were shown to depend on the mode of action of the chemicals and also varied within the chemical groups. Interaction was seen between major and minor gene(s) in the expression of cross-resistance relationships.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available