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.
This project is related to Objective 1 of this in-house project: To determine the genetic control of resistance to important diseases and pests of watermelon and release resistant lines. The F3 families used in this study were reevaluated for resistance to fusarium wilt (FW). Using an improved procedure to generate polymorphic DNA markers, we tested over 1,500 DNA markers for polymorphism. Of these markers, we identified 180 markers that were polymorphic between the parental varieties that are resistant and susceptible to FW. However, when tested with an F2 population segregating for resistance, none of these markers could be associated with the gene conferring resistance to FW resistance gene. We are screening additional DNA markers for association with FW resistance in watermelon. Through this project we have developed a new type of DNA markers named high frequency oligonucleotides-targeting active genes (HFO-TAG) that produce high polymorphism and are being used in genetic mapping and screening for markers linked to FW (race. 1)resistance in watermelon. So far, none of these markers showed association with FW (race. 1)resistance. The ARS scientists and cooperators have been communicating frequently via telephone calls and emails, and met at the Watermelon Research & Development Working Group Annual Meeting that took place in Feb. 2010 in Orlando, FL.