Author: N. Sakr 1 , 2
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  • 1 Syrian Atomic Energy Commission, Damascus, P.O. Box 6091, Syria
  • 2 INRA-UBP, UMR 1095, 234 Avenue du Brézet, 63100 Clermont-Ferrand, France
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Evolution of pathogenicity, morphological, and genetic traits were analyzed in a local Plasmopara halstedii (downy mildew) population (including two parental and five progeny isolates) multiplied under sunflower qualitative resistance selection pressure for five years. The two components of pathogenicity developed in response to Pl resistance genes selection pressure. The emergence of new virulence in P. halstedii progeny isolates carrying several levels of aggressiveness was an important consequence of selection pressure. However, appearance of new virulence did get along with evolution of aggressiveness in progeny isolates as compared with parental ones. For progeny P. halstedii isolates, an increase in pathogen virulence had direct consequences on its aggressiveness. There was no influence of selection pressure on morphological traits, but an effect was observed on evolution of genetic architecture. However, arrangement of genetic traits did get along with evolution of pathogenicity. It is clear that qualitative resistance selection pressure plays an important role in the evolution of sunflower downy mildew population.

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