Effect of root-knot nematodes (Meloidogyne spp.) on fusarium wilt in pigeonpea (Cajanus cajan)

Abstract A mixed population of root-knot nematodes ( Meloidogyne javanica and M. incognita ) applied to roots of pigeonpea seedlings caused a susceptible reaction to fusarium wilt ( Fusarium udum ) in a wilt-resistant cultivar (ICP 9145). This effect occurred not only when both organisms were added to the soil, but also when nematode and fungus were spatially separated on the plants. Spatial separation of the organisms was obtained by inoculating plants with wilt fungus by stem puncture. The ability of the nematode to affect susceptibility to F. udum in the stem is evidence for a translocatable factor or systemic effect produced by the nematode, which modifies the host response to infection by the fungus. When the experiment was repeated with a second wilt-resistant cultivar (ICP 8863), however, resistance was unaffected by the nematode. Unless the different effect of the nematode on ICP 8863 is due to its lesser susceptibility to this nematode population, it appears that either the physiology of the response to the nematodes is different, or, that the mechanism of resistance to fusarium wilt is different in the two cultivars.