Watermelon, Citrullus lanatus Thunb. Matsum. & Nakai, is an important vegetable fruit crop. China, with 68.2 million tons in production in 2009, is currently the top watermelon producer with 67.7% of the world watermelon production (FAO, 2009). Most of the Chinese watermelon varieties were bred and selected for good performance under irrigated field conditions. Many are thus intolerant to drought stress. However, in recent years, drought has become a main abiotic stress on growth and productivity of watermelon. For example, the total production in Gansu province (China) declined 50% as a result of severe drought (Feng and Wu, 2007). Drought-tolerant varieties, once developed, would be readily acceptable by the resource-poor, rain-fed, and small holder farmers. A number of drought-tolerant varieties have been developed for other crops (Fleury et al., 2010; Luigi et al., 2008), but only limited information is available for watermelon (Liu et al., 2008). Thus, identification of watermelon germplasm with drought tolerance properties is needed for the development of drought-tolerant watermelon varieties. The National Engineering Research Center for Vegetables (NERCV) and the beijing academy of Agriculture and Forestry Science introduced ≈820 randomly selected watermelon PI accessions from the Southern Regional Plant Introduction Station in Griffin, GA, in 2003 from the collection of ≈1600 accessions. we previously conducted a detailed investigation on these valuable accessions and documented 12 important agronomic traits, including fruit shapes, soluble solid contents, and rind hardness, etc. (Fan et al., 2004). However, the nature of drought tolerance on these germplasm collections has yet to be determined. In the present study, a large scale of 820 watermelon PI accessions and 246 breeding lines were evaluated for their drought tolerance properties on seedlings grown in the greenhouse under water stress conditions. The tolerance lines selected from these experiments could be valuable resources in watermelon breeding for drought tolerance.
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Comparative analyses to the first 175 most drought-tolerant Citrullus accessions for their responses to water stress treatments between two experiments.