DNA and virulence variation in a field population of Erysiphe graminis f.sp. hordei.
1992
Braendle U. | Schaffner D. | Wolfe M.S. | McDermott J.M.
Populations of Erysiphe graminis can be highly variable on a local level. The analysis of marker and haplotype frequencies clearly distinguished between populations from the different hosts, with considerable similarity between the mixture and Triton area. This suggests that in variety mixtures containing a cultivar with a recently "broken" resistance, such as Mla13 in Switzerland, the pathogen population consists to a great extent of isolates with the corresponding virulence, Va13. Nevertheless, disease severity is reduced significantly. On hosts with quantitative resistance, Va13 frequency is largely reduced even though there is obvious infection pressure from a virulent population only meters away. This is confirmed by the analysis of haplotype distribution showing that individuals are dispersed within but not necessarily between host areas. Populations from different varieties with quantitative resistance to pathogens can thus be distinguished. In aerial samples of powdery mildew, observed values of DNA haplotypes fit the expected. The negative deviation observed here suggests that a field population does not represent the total genetic variation present in an actual subpopulation.
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