Effect of Meloidogyne javanica and M. incognita on Resistance of Muskmelon Cultivars to Fusarium Wilt

A growth chamber experiment was conducted to study the interaction between Meloidogyne javanica and/or M. incognita and the Fusarium wilt fungus Fusarium oxysporum f. sp. melonis, using three muskmelon cultivars differing in their resistance to the fungus. Inoculations were carried out l. with the wilt fungus alone, 14 and 28 days after transplanting; and 2. with the wilt fungus plus one or both root-knot nematodes, either directly upon transplanting, or 14 or 28 days after transplanting. In the course of the test all muskmelon cultivars, irrespective of their initial resistance to the wilt, almost completely lost their resistance when infected with M. javanica; resistance was also impaired but to a lesser extent with M. incognita. Wilting of 100% in the resistant and moderately resistant muskmelon cultivars inoculated with M. javanica + F. oxysporum f. sp melonis occurred 14 days earlier than in muskmelon inoculated with the fungus alone. Also, M. javanica was more severe on the plants than M. incognita. In all three cultivars, both root-knot nematode species hastened expression of plant wilting, which took 12.1 days with M. javanica, 14.8 days with M. incognita, and 12.3 days with both species combined, compared with 22.7 days for plants inoculated with Fusarium oxysporum f. sp. melonis alone. Moreover, the onset of wilting required 9–13.3 days when the nematode infection preceded F. oxysporum f. sp. melonis inoculation by two weeks, compared with 16.7– 19.7 days when the nematode and fungus were inoculated simultaneously 14 days after transplanting, indicating plant preconditioning by the nematode