Modeling the dynamics of virulence genotype frequencies in barley powdery mildew populations in relation to selection and recombination
1991
Hovmoeller, M.S. | Oestergaard, H.
The present paper summarizes a model describing the dynamics of virulence genotype frequencies in aerial barley powdery mildew populations in relation to selection and recombination. Selection is caused by resistance genes in the host varieties only, leading to field specific powdery mildew subpopulations with different virulence gene frequencies. Recombination occurs within the subpopulations on single varieties, and reassortment will take place only between alleles being "unnecessary" on the varieties. In the aerial population, which is made up of a mixture of subpopulations, the selection caused by host resistance genes will finally lead to fixation of all the virulence genes selected for. Further, the selection will generate gametic disequilibrium (linkage disequilibrium) between virulence genes in the aerial population, even when there is gametic equilibrium in the previous generation. The sign of the gametic disequilibrium can be predicted in specific cases in relation to the distribution of host resistance genes in the varieties. Selection forces caused by two resistance genes present predominantly in different varieties are likely to generate negative gametic disequilibrium, whereas selection caused by two resistance genes present predominantly in the same variety is likely to generate positive gametic disequilibrium. These predictions are shown to be in accordance with observed gametic disequilibria in Danish barley powdery mildew populations
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