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Title: Identifying resistance to powdery mildew race 2W in the USDA-ARS watermelon germplasm collection

Author
item TETTEH, ANTOINIA - North Carolina State University
item WEHNER, TODD - North Carolina State University
item Davis, Angela

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2009
Publication Date: 5/6/2010
Citation: Tetteh, A.Y., Wehner, T.C., Davis, A.R. 2010. Identifying resistance to powdery mildew race 2W in the USDA-ARS watermelon germplasm collection. Crop Science. 50:933-939.

Interpretive Summary: Powdery mildew has become a common disease of watermelon in the United States. The disease can be controlled with fungicides. However, it is more economical and environmentally safe to use genetic resistance against this disease. This paper reports screening for sources of resistance to powdery mildew race 2W in the available U.S. Plant Introduction collection made of five watermelon-like species, including available watermelon cultivars. A total of 1,654 lines were tested in the greenhouse. Fifty five cultigens including the 45 most resistant and 10 checks were retested in greenhouse and field experiments. All lines showed signs of powdery mildew. But resistant plants were identified in wild types and was characterized by moderate to high variability in resistance. Eight lines showed high levels of resistance. Twenty-three lines demonstrated intermediate resistance. Leaf and stem disease severity ratings were positively correlated. Using data from the screening and retest studies, the most resistant lines were PI 632755, PI 386015, PI 346082, PI 525082, PI 432337, PI 386024, PI 269365 and PI 189225. The most susceptible accessions were PI 222775 and PI 269677. A large number of the resistant accessions originated from Nigeria and Zimbabwe.

Technical Abstract: Powdery mildew caused by Podosphaera xanthii has become a common disease of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] in the United States. The disease can be controlled with fungicides. However, it is more economical and environmentally safe to use genetic resistance against this disease. This paper reports screening for sources of resistance to powdery mildew race 2W in the available U.S. Plant Introduction collection made of four Citrullus Schrad. ex. Eckl. & Zeyh. species, and Praecitrullus fistulosus (Stocks) Pangalo species. A total of 1,654 accessions were tested in the greenhouse using seven to ten replications. From that, 55 cultigens including the 45 most resistant and 10 checks were retested in greenhouse and field experiments. All accessions and cultivars showed signs of powdery mildew. Resistance was identified in wild accessions and was characterized by moderate to high variability in resistance expression. Eight accessions showed high levels of resistance. Twenty-three accessions demonstrated intermediate resistance. Leaf and stem disease severity ratings were positively correlated (r=0.86, P=0.0001). Using data from the screening and retest studies, the most resistant accessions were PI 632755, PI 386015, PI 346082, PI 525082, PI 432337, PI 386024, PI 269365 and PI 189225. The most susceptible accessions were PI 222775 and PI 269677. A large number of resistant accessions originated from Nigeria and Zimbabwe.