Potato virus Y Resistance Breeding for the Wisconsin Potato Industry Fulladolsa Palma, A.C. 1 , Navarro, F. 2 , Jansky, S. 3 , and Charkowski, A.O. 4 Principal Investigator(s) 1 Graduate Research Assistant, 674 Russell Laboratories, University of Wisconsin, Madison, WI 53706, fulladolsapa@wisc.edu, (608) 265-3056 2 Research Program Manager, Hancock Agricultural Research Station, University of Wisconsin, Hancock, WI 54943, fmnavarro@wisc.edu, (715) 249-5961 3 Associate Professor, 341a Moore Hall - Plant Sciences, USDA-ARS and University of Wisconsin, Madison, WI 53706, shjansky@wisc.edu, (608) 262-8324 4 Professor, 682 Russell Laboratories, University of Wisconsin, Madison, WI 53706, acharkowski@wisc.edu, (608) 262-7911 Collaborator(s) Dennis Halterman, Research Geneticist, USDA-ARS Vegetable Crops Research Unit, Madison, WI 53706, dennis.halterman@ars.usda.gov, (608) 265-2144 Summary - A number of breeding clones available to the UW Potato Breeding Program carry Potato virus Y (PVY) resistance genes derived from different wild relatives of cultivated potato. - The molecular markers RYSC3 for detection of the Ry adg resistance gene and YES3-3B for detection of the Ry sto resistance gene correlate well with the resistance phenotype and were used to identify resistant parents that were later crossed with susceptible parents that have desirable traits. - Molecular marker data analysis indicates that the resistance genes Ry adg and Ry sto are single dominant genes, found in simplex (Rrrr) in the evaluated tetraploid populations. - The Ry chc gene has also been identified in certain breeding clones. Genome sequencing data of one of these plants is being used to develop a molecular marker to be used as a tool for incorporating this third source of resistance into Wisconsin potato varieties. Introduction Viruses are among the most common plant pathogens and are easily spread through vegetative propagation. Over 30 viruses are known to infect potato. Potato virus Y (PVY) is the most economically important disease problem for production of seed potatoes in many areas of the world (Gray et al., 2010). In the last decade, PVY has been the cause 97% of rejections of Wisconsin seed lots due to plant pathogens (Frost et al., 2013). Detection of PVY in potatoes mostly relies on visual inspection of plants in the field and identification of symptoms. Infected plants show symptoms that range from mild to severe mosaic, leaf drop, leaf crinkle, leaf chlorosis, leaf necrosis, cracking and necrotic rings on tubers (Gray et al., 2010). The UW Potato Breeding Program, like other potato breeding programs across the country, has traditionally used the method of phenotypic recurrent selection to develop new cultivars. This method begins with the selection of diverse, desirable tetraploid 75