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Abstract
Genetic origin of five progeny Plasmopara halstedii (downy mildew) isolates of races 300, 304, 314, 704 and 714 obtained after 5 years of sunflower mono-culture infected with two parental isolates of races 100 and 710 was studied using 12 EST-derived markers. The isolates of races 714, 704 and 314 had an intermediary genetic position between the two parental isolates of races 100 and 710. The three isolates of races 100, 300 and 304 were localised in the same genetic clade. Two mechanisms could explain the emergence of new virulence in P. halstedii as recombination between races and mutations in a clonal lineage.
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Acknowledgements
The author thanks the Syrian Commission of Atomic Energy for a financial support concerning his work.