2012 Annual Report 1a.Objectives (from AD-416): Knock down candidate susceptiblity genes in transgenic grapes and assay disease resistance; conduct ecoTILLING in the vinifera germplasm collection and self-hybridize susceptible heterozygotes. 1b.Approach (from AD-416): We have identified orthologous candidate genes shown to be required for susceptiblity to Arabidopsis powdery mildew and are cloning these genes into silencing constructs. We will outsource the stable transformation of susceptible grapes with these constructs and test their resistance. Transformations will be conducted at the Ralph M. Parsons Plant Transformation Facility. 3.Progress Report: The highest quality Vitis vinifera grape cultivars are highly susceptible to powdery mildew. Grape growers desire vinifera cultivars with powdery mildew resistance for reduced inputs, which is the goal of this project. Previously, we computationally identified the evolutionary orthologues (i.e., the most closely related genes) of two resistance genes and selected six candidates. For each of these, we developed silencing constructs to test gene function and identify genes in which we could find natural mutations for traditional breeding of disease resistant vinifera grape cultivars. We generated several hundred Vitis vinifera vines and tested a subset for improved resistance to powdery mildew. We showed that silencing individual grape genes can result in reduced susceptibility to powdery mildew, decreasing disease by up to 80% on individual vines. Related to this, we characterized natural variation in these candidate genes by screening the USDA-ARS germplasm repository. We showed that these candidates are highly conserved with very few natural mutations occurring protein-coding exons.