نبذة مختصرة : International audience ; A promising strategy to manage plant pathogen in agriculture is growing diversified mixtures of resistant varieties. The success of these strategies requires the existence of host genotype by parasite genotype (G*G) interactions revealing fitness costs associated with gains in infectivity on resistant cultivars. Indeed, the resulting antagonistic interactions limit the range of possible adaptive variations. Here, we inoculated 422 downy mildew (DM) isolates, collected in commercial fields in Southern France, to the four grapevine cultivars Cabernet-Sauvignon (a susceptible cultivar), Regent (carrying the resistance factor Rpv3.1), Bouquet (carrying Rpv1) and Artaban (carrying both Rpv3.1 and Rpv1). During experiments, conducted in laboratory conditions conducive for disease expression, we measured for each G*G interaction two pathogen life-history traits : the infection efficiency and the intensity of sporulation. At the scale of the DM population, resistant cultivars efficiently reduce sporulation. The average percentage of sporulation reduction for isolates sampled on susceptible varieties are 71%, 78%, 93% on Rpv1, Rpv3 and Rpv1/Rpv3, respectively. Moreover, DM experience few (if any) cost of adaptation, with variation of sporulation of-5%, + 48% and +12% for isolates sampled on Rpv3, Rpv1 and Rpv1/Rpv3, respectively, and inoculated on susceptible varieties. At the scale of the DM individual isolate, only positive correlations (ranging from 0.20 to 0.72) between the sporulation intensity among the 6 combinations of cultivars considered were observed. The abscence of any trade-off goes together with an absence of antagonistic interactions between these cultivars despiste their diverse genetic background. Altogether these results question the efficiency of diversification strategies relying on Rpv1 and Rpv3 factors to control grapevine DM. These results should however be taken with caution, as we only focus on a few traits of DM life cycle. Adaptation trade-offs between resistance ...
No Comments.