Evolution of pathogenicity in Plasmopara halstedii (sunflower downy mildew)

Abstract

Comprehension of the processes of co-evolution between the pathogen and its host plant is very important, particularly in the case of obligate pathogen as Plasmopara halstedii which cannot develop only on sunflower. The influence of selection pressure exercised by qualitative resistance in sunflower plants on evolution of pathogenicity was analysed in pathogenic populations of P. halstedii. This selection pressure led a new virulence to appear in P. halstedii isolates carrying several levels of aggressiveness. It seems that the qualitative resistance selection pressure plays an important role in the evolution of this pathogen, and these changes on the level of pathogenicity may help to a better adaptation of P. halstedii in the presence of intensive use of qualitative resistance.

Keywords:

• aggressiveness
• qualitative resistance
• virulence
• selection pressure

Acknowledgement

The author would like to thank the Syrian Commission of Atomic Energy for providing financial support for this study.