Graduate Thesis Or Dissertation

 

Effect of wheat cultivar mixtures on populations of Puccinia striiformis races Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xp68kj628

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  • This study quantified the frequency of simple versus complex races of Puccinia striiformis Westend. in mixtures of wheat cultivars possessing different race-specific resistance genes. A simple race of a pathogen can infect only one component, and a complex race of the pathogen can infect two or more components of an intraspecific plant mixture. The treatments were designed so that the race that was complex changed depending on the host mixture, thus enabling us to observe the influence of pathogen complexity in different host genetic backgrounds. Six cultivar mixtures and one pure stand of winter wheat were inoculated with three races of P. striiformis (CDL 27, CDL 29, and CDL 41) at two locations for two seasons. Potted plants of three winter wheat cultivars (Paha, Tres, and Tyee) that were each susceptible to one of the three races of the pathogen were used to sample the pathogen during the field epidemics. Disease incidence on the differential cultivars was used to calculate the proportion of the three races in each treatment. The specific cultivars included in the mixtures influenced the frequencies of the three races. Increasing the number of virulent races in a mixture reduced the frequency of the complex race relative to the other two races. When two of the races (races 29 and 41) were complex on the same mixture, location had an effect on which of the races was more frequent. When race 29 was the complex race in the mixture, it was more frequent than when race 41 was the complex race. The results suggest that environmental interactions, genetic background of the pathogen race, host composition, and interaction among pathogen races may be as important in determining race frequencies in mixtures as is stabilizing selection sensu Vanderplank (1968).
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