QTL Associated with Resistance to Bacterial Spot Race T4 in Tomato

Resistance to bacterial spot (Xanthomonas perforans) race T4 has been characterized in Florida tomato (Solanum lycopersicum) breeding lines Fla. 8517, Fla. 8233 and Fla. 8326. F2 populations derived from crosses between each of these lines and one or both of the susceptible breeding lines Fla. 7946 and Fla. 8111 were evaluated in Fall 2008 and Fall 2009 to confirm and quantify effects of previously identified QTL. A chromosome 11 QTL derived from Hawaii 7998, which is in the pedigree of each resistant line, was confirmed in all populations as a major contributor to resistance. This locus appears distinct from the bacterial spot race T3 hypersensitivity gene Rx-4, that was recently mapped to chromosome 11. A marker linked to the I-3 gene on chromosome 7, which confers resistance to Fusarium wilt race 3 (Fusarium oxysporum Schlecht. f. sp. lycopersici Snyder & Hansen), was strongly associated with susceptibility to bacterial spot race T4 in all populations involving Fla. 7946—the only line containing I-3. In the Fla. 8517 population, two QTL on chromosomes 3 and 12 contributed minor effects towards resistance and susceptibility, respectively.