ORIGINAL ARTICLE
Analyzing the influence of qualitative resistance selection pressure on variation of aggressiveness in Plasmopara halstedii
 
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1
Syrian Atomic Energy Commission, Damascus, P.O. Box 6091, Syria
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INRA-UBP, UMR 1095, 234 Avenue du Brézet, 63100 Clermont-Ferrand, France
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UBP-UHR 1095, 24 Avenue des Landais, 63/77, Aubiére, France
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INRA-UHR 1065, La Grande Ferrade, BP81, 33883 Villenave d’Ornon Ceder, France
CORRESPONDING AUTHOR
Nachaat Sakr
Syrian Atomic Energy Commission, Damascus, P.O. Box 6091, Syria
 
Journal of Plant Protection Research 2011;51(2):140–144
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ABSTRACT
Variation of aggressiveness in populations of race 710 of Plasmopara halstedii [(Farl.) Berl. et Toni] (sunflower downy mildew) was measured under different strategies of qualitative resistance selection pressure: mixture, alternation and monoculture of major resistance genes in comparison with a population under no selection pressure. Two sunflower lines showing different levels of quantitative resistance were used to measure four aggressiveness criteria: percentage infection, latent period, sporulation density and reduction of hypocotyl length. P. halstedii strains multiplied under varietal mixtures presented the greatest sporulation densities and shortest hypocotyl lengths, those multiplied under alternation presented a reduced latent period and shorter hypocotyl lengths compared with those not influenced by selection pressure. There were no significant differences between populations multiplied under monoculture of resistance genes and those under no selection pressure. These changes appear as being linked to the number of infected plants present. The results suggested that the method of Pl gene management affects aggressiveness because it determines the number of susceptible plants harbored by the parasite.
CONFLICT OF INTEREST
The authors have declared that no conflict of interests exist.
 
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