Rootstock Assessment for Root-knot Nematode Management in Grafted Honeydew Melon

Root-knot nematodes (RKN) are one of the most damaging soilborne pathogens of honeydew melon (Cucumis melo var. inodorus). Currently their management is dependent on soil fumigation. Vegetable grafting with resistant rootstocks may be an effective approach for RKN management in the sustainable production of honeydew melons. However, RKN-resistant rootstocks for melon grafting currently are not commercially available. Cucumis metulifer has been shown to be resistant to RKN, but little is known about its suitability as a rootstock for grafted honeydew melons. In this greenhouse study, we grafted honeydew melon ‘Honey Yellow’ onto C. metulifer (‘Honey Yellow’/C. metulifer) and a commercial cucurbit rootstock ‘Strong Tosa’ (Cucurbita maxima × C. moschata) (‘Honey Yellow’/‘Strong Tosa’). Non-grafted and self-grafted ‘Honey Yellow’, C. metulifer, and ‘Strong Tosa’ were included as controls. Plants were inoculated with eggs of Meloidogyne incognita race 1 at a density of 5,000 eggs/plant and grown in 3 L pots for eight weeks. Results showed that non-grafted and self-grafted C. metulifer, and ‘Honey Yellow’/C. metulifer had significantly lower (P < 0. 05) gall and egg mass ratings compared to non-grafted and self-grafted ‘Honey Yellow’ and ‘Strong Tosa’, and ‘Honey Yellow’/‘Strong Tosa’. No significant differences were observed between non-grafted C. metulifer and ‘Honey Yellow’/C. metulifer. In addition, nematode eggs extracted from roots of non-grafted C. metulifer and ‘Honey Yellow’/C. metulifer were 2,395 and 3,339 eggs/plant, respectively, which were significantly lower than that extracted from non-grafted ‘Honey Yellow’ (110,027 eggs/plant), non-grafted ‘Strong Tosa’ (145,280 eggs/plant), and ‘Honey Yellow’/‘Strong Tosa’ (68,003 eggs/plant). These results suggest that C. metulifer was resistant to M. incognita and grafting the susceptible melon scion onto C. metulifer did not affect its resistance. In addition, self-grafting did not impact resistance of C. metulifer or susceptibility of ‘Honey Yellow’ and ‘Strong Tosa’ based on galling and egg mass ratings and extracted egg numbers. ‘Honey Yellow’/C. metulifer showed significantly higher shoot dry weight but did not influence shoot fresh weight, stem length, and total leaf area, compared to that of non-grafted ‘Honey Yellow’. Despite the susceptibility to M. incognita in the ‘Strong Tosa’ rootstock, ‘Honey Yellow’/‘Strong Tosa’ demonstrated higher shoot dry weight and larger total leaf area than non-grafted ‘Honey Yellow’ and ‘Honey Yellow’/C. metulifer. Field evaluations need to be performed to fully assess the potential of C. metulifer as a suitable rootstock for managing RKN and improving fruit yield in honeydew melon production.