New sources of resistance to gummy stem blight in watermelon

Gummy stem blight, caused by Didymella bryoniae (Auersw.) Rehm, is a major disease of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai]. Plant breeders need sources of resistance that can be incorporated into adapted breeding lines to help control the disease. We tested all the available accessions from the USDA-ARS watermelon germplasm collection, including C. lanatus var. citroides (L.H. Bailey) Mansf., for resistance to gummy stem blight. The experiment was a randomized complete block with 1332 cultigens, two sites (Held and greenhouse), two or four replications, and two to six plants per plot. The resistant check was PI 189225 and the susceptible check was 'Charleston Gray'. PI 279461, PI 482379, PI 254744, PI 526233, PI 482276, PI 271771, PI 164248, PI 244019, PI 296332, and PI 490383 were selected as the most resistant cultigens to be used in future breeding efforts. The most susceptible cultigens were PI 183398, PI 169286, PI 223764, PI 226445, PI 525084, PI 534597, and PI 278041.