Abstract
Southern root-knot nematode (RKN, Meloidogyne incognita) is a serious pest of cultivated watermelon (Citrullus lanatus var. lanatus) in southern regions of the United States and no resistance is known to exist in commercial watermelon cultivars. Wild watermelon relatives (Citrullus lanatus var. citroides) have been shown in greenhouse studies to possess varying degrees of resistance to RKN species. Experiments were conducted over 2 yr to assess resistance of southern RKN in C. lanatus var. citroides accessions from the U.S. Watermelon Plant Introduction Collection in an artificially infested field site at the U.S. Vegetable Laboratory in Charleston, SC. In the first study (2006), 19 accessions of C. lanatus var. citroides were compared with reference entries of Citrullus colocynthis and C. lanatus var. lanatus. Of the wild watermelon accessions, two entries exhibited significantly less galling than all other entries. Five of the best performing C. lanatus var. citroides accessions were evaluated with and without nematicide at the same field site in 2007. Citrullus lanatus var. citroides accessions performed better than C. lanatus var. lanatus and C. colocynthis. Overall, most entries of C. lanatus var. citroides performed similarly with and without nematicide treatment in regard to root galling, visible egg masses, vine vigor, and root mass. In both years of field evaluations, most C. lanatus var. citroides accessions showed lesser degrees of nematode reproduction and higher vigor and root mass than C. colocynthis and C. lanatus var. lanatus. The results of these two field evaluations suggest that wild watermelon populations may be useful sources of resistance to southern RKN.
Highlights
Southern root-knot nematode (RKN, Meloidogyne incognita) is a serious pest of cultivated watermelon (Citrullus lanatus var. lanatus) in southern regions of the United States and no resistance is known to exist in commercial watermelon cultivars
The objectives of the studies reported in this paper were (i) to evaluate the potential contribution of moderately resistant watermelon accessions to suppression of RKN and associated damage in fields infested with M. incognita and (ii) to compare selected watermelon accessions in nematicide-treated and nontreated soils to determine the effectiveness of host resistance for managing M. incognita
23 different Plant Introduction (PI) accessions representing Citrullus lanatus var. citroides, C. lanatus var. lanatus, and C. colocynthis, originating from eight different countries, were evaluated in a field infested with M. incognita, and several of the C. lanatus var. citroides accessions evaluated exhibited resistance to that nematode
Summary
Characterization of resistance to root-knot nematode in Citrullus lanatus var. Citroides accessions: A field site at the U.S Vegetable Lab in Charleston, SC, was infested with M. incognita by planting experimental plots with ‘PA 136’ pepper (Capsicum annuum L.) grown and inoculated with. Twenty-three accessions from the U.S Plant Introduction (PI) Watermelon Collection of C. lanatus var. Four watermelon cultivars (Ojakkyo, Dixie Lee, Charleston Gray, and Crimson Sweet) were selected as reference entries (Table 1). C. colocynthis and the cultivars Charleston Gray, Crimson Sweet, and Dixie Lee were determined to be susceptible to M. incognita race 3 (Thies and Levi, 2003). Root systems of each plant were stained using the method of Thies et al (2002) and evaluated for severity of galling, egg mass production, and root system fibrosity.
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