Poster Session: Biology and Disease Management - Genetics of Resistance
336-P
Strategies for durable resistance to the grapevine powdery mildew fungus, Erysiphe necator.
L. CADLE-DAVIDSON (1)
(1) USDA ARS GGRU, Geneva, NY, U.S.A.
Nearly all cultivars of Vitis vinifera are highly susceptible to the grapevine powdery mildew fungus, Erysiphe necator. Grape breeders around the world are working to introgress resistance from wild Vitis. Of the widely-used introgressions, most involve dominant, race-specific resistance phenotypes typified by R-genes. In an effort to identify resistance gene combinations that may result in improved durability, we developed a set of E. necator isolates based on their phenotype on the NB-LRR gene Run1, which is the best characterized and most widely used R-gene in grapevine. This E. necator set represents wild-type individuals unable to colonize Run1 vines, individuals with long latent periods on Run1 vines, and individuals that infect Run1 vines as if no R-gene were present. Having tested this set on ten sources of resistance, the results generally suggest that dominant R-genes will not improve the efficacy nor spectrum of resistance. Weaker R-genes hold some promise for protecting Run1 but will not prevent selection for virulence. The exceptions to these generalizations include the Ren4 resistance gene, for which no virulent isolates have yet been identified, and two recessive resistance genes. Because grape breeders are actively stacking R-genes, plant pathology-based research and guidance are urgently needed to increase the likelihood that new powdery mildew resistant varieties will be durable.