2012 Annual Report 1a.Objectives (from AD-416): Verticillium wilt (VW) of potato is a widespread and persistent problem in virtually all significant production areas in the United States. The only successful control strategy currently available to growers is soil fumigation, which is expensive and environmentally harmful. Host plant resistance offers the most cost-effective long-term control strategy for VW. One likely candidate for a potato VW resistance (R) gene is an ortholog of the tomato Ve gene, which has been cloned and found to confer immunity to VW. We have recently developed a molecular marker within a Ve-like gene from resistant potato and found that this marker co-segregates with the VW resistance phenotype in a segregating population. Our specific objectives are to: 1. Identify germplasm that has been previously documented to be either resistant or susceptible to VW and verify the resistance phenotype using quantitative PCR. 2. Amplify and sequence Ve orthologs from the resistant and susceptible individuals for use in identifying single nucleotide polymorphisms that differentiate resistant from susceptible Ve alleles. 1b.Approach (from AD-416): Inoculations of seedlings from crosses between cultivated breeding parents, phenotypic characterization of the inoculated seedlings, stem DNA extraction and quantitative PCR. 3.Progress Report: We have developed a molecular assay that allows us to monitor the abundance of the Verticillium fungus by determining the amount of deoxyribonucleic acid (DNA) present within the potato plant. Over the past year, we have refined and optimized this assay by identifying which regions of the fungal DNA work best for the assay and correlate best with the amount of fungus present within the stems. We have begun using this assay to further define the interaction between Verticillium and potato in populations derived from popular varieties. Using this method we can now better differentiate resistant and susceptible potato plants in the field and in the greenhouse. This greatly improves our ability to quantitate the pathogen compared to traditional assays that were not only time consuming, but also could not reliably predict whether a plant was resistant. This research relates to Objective 1, Develop adapted potato clones with enhanced resistance to major potato diseases.