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  • Author or Editor: Sharon Buckner x
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Southern root-knot nematodes (Meloidogyne incognita) are an important re-emerging pest of watermelon in the United States and worldwide. The re-emergence of root-knot nematodes (RKNs) in watermelon and other cucurbits is largely the result of the intensive cultivation of vegetable crops on limited agricultural lands coupled with the loss of methyl bromide for pre-plant soil fumigation, which has been the primary method for control of RKNs and many soilborne diseases of cucurbits and other vegetable crops for several decades. One alternative for managing RKN in watermelon is the use of resistant rootstocks for grafted watermelon. We have developed several RKN-resistant Citrullus lanatus var. citroides lines (designated RKVL for Root-Knot Vegetable Laboratory), which have shown promise as rootstocks for grafted watermelon. In 2011 and 2012, we demonstrated that F1 hybrids derived from our selected RKVL lines exhibited resistance to RKN that was equal to or greater than that of the parental RKVL lines when grown in fields highly infested with M. incognita. In 2011, although significant differences were not observed among rootstocks, the F1 hybrids produced slightly higher yields compared with the selected parental lines. Among the selected parental lines, RKVL 318 produced high yields in both years. In 2011, three of four RKVL parental lines and all four of their F1 hybrids produced greater (P < 0.05) fruit yields than self-grafted ‘Tri-X 313’, ‘Emphasis’ bottle gourd, and ‘Strong Tosa’ squash hybrid. In 2012, three RKVL F1 hybrid lines produced higher yields than the selected parents. Overall, these F1 hybrids were vigorous and should provide useful genetic material for selection and development of robust RKN-resistant C. lanatus var. citroides rootstock lines.

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Root-knot nematode-resistant rootstock lines (designated RKVL for Root-Knot Vegetable Laboratory) derived from wild watermelon (Citrullus lanatus var. citroides) were compared with wild tinda (Praecitrullus fistulosus) lines and commercial cucurbit rootstock cultivars for grafting of seedless triploid watermelon ‘Tri-X 313’ (C. lanatus var. lanatus) in a field infested with the southern root-knot nematode (RKN) (Meloidogyne incognita) in Charleston, SC, during 2009 and 2010. In both years, RKN infection was severe in ‘Emphasis’ bottle gourd, ‘Strong Tosa’ hybrid squash, and wild tinda rootstocks with galling of the root system ranging from 86% to 100%. In 2009, the RKVL wild watermelon rootstocks exhibited lower (P < 0.05) percentages of root galling (range 9% to 16%) than non-grafted ‘Tri-X 313’ (41%), ‘Emphasis’, ‘Strong Tosa’, and the wild tinda rootstocks. The grafted wild watermelon rootstock RKVL 318 produced more (P ≤ 0.05) fruit (12 per plot) than all other entries (mean = five per plot), and it produced a heavier (P ≤ 0.05) fruit yield (29.5 kg per plot) than all entries except self-grafted ‘Tri-X 313’ (21.5 kg per plot). In 2010, soil in half of the plots was treated with methyl bromide (50%):chloropicrin (50%) (392 kg·ha–1) before planting. The RKVL wild watermelon rootstocks exhibited resistance to RKN with percentages of root system galled ranging from 11% for RKVL 316 to 56% for RKVL 301 in the untreated control plots. Fruit yields in the untreated plots were 21.9, 25.6, and 19.9 kg/plot for RKVL 301, RKVL 316, and RKVL 318, respectively. Yields were greater (P ≤ 0.05) for the three RKVL rootstocks than for ‘Strong Tosa’ (3.0 kg) and ‘Ojakkyo’ wild watermelon rootstock (2.8 kg) in the untreated plots. Yields of watermelon grafted on ‘Strong Tosa’ were nearly seven times greater (P ≤ 0.05) in the methyl bromide-treated plots than in the untreated plots. In contrast, yields of RKVL 316 and RKVL 318 were similar in both treatments and the yield of RKVL 301 was less (P ≤ 0.05) in the methyl bromide-treated plots than in the untreated plots. The three RKVL wild watermelon rootstock lines exhibited resistance to RKN. RKVL 316 had low root galling and produced the heaviest fruit yield and greatest numbers of fruit of any rootstock evaluated in 2010. The RKVL lines should be useful sources of RKN resistance for rootstocks for grafted watermelon.

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