A perspective on breeding and implementing durable powdery mildew resistance

Abstract

A strong international effort has resulted in the discovery of a dozen powdery mildew resistance loci in grapevine, and their introgression into cultivated grapevines could have a multibillion dollar economic impact. However, some of the resistance loci have minor effects, and most have been shown to be race specific. One approach to combat virulent pathogen strains overcoming race-specific resistance is to stack multiple resistance genes in a single cultivar, but this creates challenges for generating additional seedlings, selecting which genes to use, tracking them with DNA markers, and validating the added value of stacked genes. To identify complementary sets of resistance loci, breeders and pathologists on the US VitisGen grape breeding project developed a strategy to evaluate various resistance gene stacks against phenotypically and genetically diverse isolates of powdery mildew (Erysiphe necator) collected from the eastern US center of diversity. Leveraging the pathogen genetic diversity provides a crystal ball to predict selection for virulence after commercialization. However, even if this approach successfully identifies complementary stacked resistance genes and these become widely adopted in commercial cultivars, history suggests the pathogen will eventually adapt and win. Thus, we must consider complementary disease management tactics and strongly encourage growers to protect this new generation of disease-resistant cultivars. With a coordinated effort, we aim to make powdery mildew resistance breeding easy, efficient, and effective, and to provide the viticultural strategies to protect this investment for future generations of grape growers around the world.