2007 Annual Report 1a.Objectives (from AD-416) Evaluate diploid and tetraploid potato germplasm for resistance to early blight and late blight. 1b.Approach (from AD-416) REPLICATED TRIATS WILL BE PLANTED IN NON-COMMERICAL POTATO PRODUCTION AREAS IN PENNSYLVANIA AND ARTIFICIALLY INOCULATED 8-10 WEEKS AFTER PLANTING TO INDUCE EITHER LATE BLIGHT OR EARLY BLIGHT EPIDEMICS. PLANTS WILL BE SCORED WEEKLY FOR PERCENT INFECTED FOLIAGE DURING THE COURSE OF THE EPIDEMIC. 3.Progress Report This report serves to document research conducted under a Specific Cooperative Agreement between ARS and The Pennsylvania State University. Additional details of research can be found in the report for the parent project 1275-21000-176-00D ‘Genetic enhancement of potatoes for nutritional and processing quality and for resistance to diseases’. Phytophthora infestans, the causal agent of potato late blight, has overcome previously identified genetic sources of resistance. New sources of resistance must be identified to minimize the losses caused by this disease. Recurrent maternal selection has been used to generate a potato population with improved levels of resistance to late blight. A second planting of seedlings were planted in the greenhouse to advance the population to the third cycle of selection after the first planting failed due to poor growing conditions in the hoophouse. Efforts to develop molecular markers linked to previously identified resistance loci were only partially successful, most likely because many more genes for resistance to late blight exist in the population than have yet been identified. This emphasizes the importance of population improvement efforts even when molecular tools are available. Although genetic evaluations of breeding material require several years of testing, we developed a genetic model that would identify superior parents and parental combinations even when susceptible offspring are discarded from further evaluation. This greatly lessens the space, time, labor and other resources needed to develop superior breeding materials. It has been difficult to incorporate resistance to Alternaria solani, the causal agent of potato early blight, into commercial quality germplasm because of its association with lateness and low yields. Recurrent maternal selection has been used to generate a potato population with improved levels of resistance to early blight. This population is in the process of being evaluated for resistance to early blight and maturity this year. This research will furnish late blight and early blight resistant breeding materials to other potato breeders to develop disease resistant cultivars. Ultimately growers and consumers will benefit when disease resistant cultivars become available. Progress is being monitored by frequent email correspondence.