Inhibitory Effect of Watermelon Mosaic Virus on Meloidogyne javanica (Treub) Chitwood Infecting Cucurbita pepo L.

Interactions between root-knot nematodes and viruses were recently reviewed by Taylor (4). Compared to virus-free cowpea (vigna sinensis Endl.), cowpea mosaic virus-infected plants formed fewer galls on roots in response to infection by Meloidogyne incognita (Kofoid and White) Chitwood (2). On the other hand, tobacco plants (Nicotiana tabacum L.) infected with tobacco ringspot virus (TRSV) and M. incognita had more galls than did nematode-infected virus-free plants (4). Also, TRSV-infected bean plants (Phaseolus vulgaris L.) had more second-stage juveniles of M. javanica (Treub) Chitwood entering roots than did virus-noninfected plants, whereas tobacco mosaic virus (TMV) did not show similar influence on the nematode in tomato plants (Lycopersicon esculentum Mill.) (1). Tomato plants infected with TMV induced higher growth rates of the nematode than did virus-free plants, whereas TRSV in bean plants did not affect the rates (1). Similarly, Bird (1) found no synergistic effect between M. javanica and TRSV on bean root, but the effect on soybean (Glycine max (L.) Merr.) betweenM, incognita acrita and TRSV was reported by Ryder and Crittenden (3). Clearly, interactions between viruses and root knot nematodes on host plants are complex.