Watermelon (C. lanatus var. lanatus) is an important vegetable crop grown in the United States with an annual production of 2.1 million tons and a farm value of $435 million (U.S. Department of Agriculture [USDA], 2007). Root-knot nematodes (Meloidogyne spp.) cause extensive damage to watermelon throughout the southern United States (Sumner and Johnson, 1973; Thies, 1996; Thomason and McKinney, 1959; Winstead and Riggs, 1959) and increase the severity of Fusarium wilt in watermelon fields (Sumner and Johnson, 1973).
Root-knot nematodes are primarily controlled in watermelon by fumigation with methyl bromide. Approximately 6% of all methyl bromide treatments in vegetable crops throughout the world are for watermelon and melon (Cucumis melo L.) (USDA, 1993). However, use of methyl bromide is being phased out in the United States (U.S. Environmental Protection Agency, 2000). The loss of methyl bromide for preplant soil fumigation was predicted to result in annual yield losses of 15% to 20% for watermelon in Georgia and Florida (Lynch and Carpenter, 1999). The removal of methyl bromide from the U.S. market has raised great interest in developing an alternative approach for managing root-knot nematodes in vegetable crops. Host plant resistance would provide an economical and environmentally friendly alternative for managing root-knot nematodes in watermelon.
There are several reports describing the reactions of cultivated watermelon to root-knot nematodes. Seventy-eight watermelon cultivars and five breeding lines evaluated for response to root-knot nematode were all susceptible (Winstead and Riggs, 1959). Similarly, 10 watermelon cultivars evaluated in Puerto Rico were all susceptible to M. incognita (Montalvo and Esnard, 1994). Thomason and McKinney (1959) reported that the watermelon cultivar ‘Striped Klondike’ was susceptible to M. incognita acrita and M. javanica.
In a recent study, we optimized a procedure for evaluating U.S. PIs of Citrullus spp. for resistance to root-knot nematodes (Thies and Levi, 2003). In that study, moderate resistance to M. arenaria race 1 was identified among C. lanatus var. citroides PIs. The objective of this study was to evaluate the group of C. lanatus var. citroides PIs that showed moderate resistance to M. arenaria race 1 for resistances to M. incognita race 3 and M. arenaria race 2.
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U.S. Environmental Protection Agency 2000 Protection of stratospheric ozone: Incorporation of Clean Air Act amendments for reductions in Class I, Group VI controlled substances Fed. Reg. 65 70795 70804