ARS | Publication request: Sources of resistance to race 2WF powdery mildew in U.S. watermelon plant introductions

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 8, 2011
Publication Date: October 20, 2011
Citation: Zhang, H., Guo, S., Gong, G., Ren, Y., Davis, A.R., Yong, X. 2011. Sources of resistance to race 2WF powdery mildew in U.S. watermelon plant introductions. HortScience. 46(10):1349-1352.

Interpretive Summary: Powdery mildew is an economically important foliar disease which is now common in watermelon. This disease occurs in all watermelon growing areas and can reduce yields by up to 30%. Finding and breeding for resistance to this disease is important to reduce dependence on fungicides, and to use in combination with fungicides to limit the spread of fungicide-resistant pathogens. Watermelon plant introductions (PI) resistant to this disease should be a valuable source of germplasm in watermelon breeding programs. We evaluated 2100 PI families, representing 820 PI lines from the U.S. Citrullus sp. PI collection, for resistance to powdery mildew. The lines represent three species, watermelon (766), a subspecies of watermelon (53) and related species (1). Resistance was detected in eleven PI lines 482246, PI 482283, PI 500307, PI 482324, PI 482308, PI 482322, PI 482321, PI 482276, PI 482319, PI 482335, and PI 482350 and intermediate resistance was detected in another 16 lines. The majority of the resistant accessions were collected in Africa and include 11 watermelon and 16 watermelon subspecies.

Technical Abstract: Powdery mildew [Podosphaera xanthii (Castagne) Braun & Shishkoff (syn. Sphaerotheca fuliginea auct. p.p.)], is an economically important foliar disease now common in watermelon [Citrullus lanatus (Thunb.) Mastum. & Nakai]. This disease occurs in all watermelon growing areas and can reduce yields by up to 30%. Finding and breeding for resistance to this disease is important to reduce dependence on fungicides, and to use in combination with fungicides to limit the spread of fungicide-resistant P. xanthii. Races 2WF of P. xanthii is the prevalent isolate of powdery mildew in Beijing. Watermelon plant introductions (PI) resistant to this disease should be a valuable source of germplasm in watermelon breeding programs. We evaluated 2100 PI S1 families, representing selfed lines from 820 accessions from the U.S. Citrullus sp. PI collection, for resistance to race 2WF powdery mildew. The accessions represent three species, C. lanatus var. lanatus (766), C. lanatus var. citroides (L. H. Bailey) Mansf. (53) and C. colocynthis (L.) Schrad. (1). Resistance was detected in eleven PI lines PI 482246, PI 482283, PI 500307, PI 482324, PI 482308, PI 482322, PI 482321, PI 482276, PI 482319, PI 482335, and PI 482350 and intermediate resistance was detected in another 16 lines. The majority of the resistant accessions were collected in Africa and include 11 Citrullus lanatus var. lanatus and 16 C. lanatus var. citroides.