2012 Annual Report 1a.Objectives (from AD-416): To map and develop molecular markers linked to the fusarium wilt resistance (race. 1)gene in watermelon. 1b.Approach (from AD-416): The cooperator has developed parental lines and BC1 and F2 populations segregating for FW (race. 1)resistance. Previous experiments conducted by the cooperator with these populations showed that the FW (race. 1)resistance is controlled by a single dominant gene. The cooperator grew 200 F2 plants and collected leaf samples for DNA analysis from each of these F2 plants. The cooperator is self-pollinating each of the F2 plants in order to produce F3 families. These F3 families will be used by the cooperator for progeny evaluation and identifying the FW (race. 1)resistant and susceptible F2 plants. The cooperator will provide ARS the F3 progeny evaluation data and leaf samples of the F2 plants (and their resistant and susceptible parental lines). The ARS scientists will isolate DNA from each of the parental lines and F2 leaf samples, and conduct genetic mapping analysis to identify markers linked to the FW-resistance gene. 3.Progress Report: This project corresponds with in-house Objective 1: Determine the genetic control of resistance to important diseases and pests of watermelon and release resistant breeding lines developed. A large number of randomly amplified polymorphic DNA and high-frequency, oligonucleotides targeting active genes markers were screened for the parental lines and bulked samples of resistant and susceptible genotypes. Although we identified several hundred polymorphic markers, we were not able to identify any marker significantly associated with the gene conferring resistance to Fusarium wilt, race 1, in watermelon. However, we have isolated high-quality DNA from the segregating F2 population and are planning to use the Genotyping-by-Sequencing procedure for this population set to discover a large number of single nucleotide polymorphism markers, as done in recent collaboration with the Institute of Genetic Diversity, Cornell University. The ARS scientists and cooperators are communicating frequently via telephone calls and emails, and have met at the Watermelon Research & Development Working Group Annual Meeting that took place in February, 2011.