INTERACTIONS BETWEEN FUSARIUM-OXYSPORUM F-SP TRACHEIPHILUM AND MELOIDOGYNE SPP IN VIGNA-UNGUICULATA .1. EFFECTS OF DIFFERENT INOCULUM DENSITIES ON FUSARIUM-WILT

The effects of chlamydospores and conidia of Fusarium oxysporum f.sp. tracheiphilum at different initial spore concentrations were compared in the wilt-susceptible cowpea cultivar California Blackeye No. 5 (CB5). In glasshouse experiments with one inoculum density of either Meloidogyne incognita or M. javanica, chlamydospores resulted in greater incidence and severity of Fusarium wilt than conidia at the same inoculum densities. Wilt symptoms also increased on wilt-resistant cultivar CB3 as inoculum densities of M. javanica were increased. When three cultivars were infested with moderate or high densities of both F. o. tracheiphilum and M. javanica, only CB5 developed severe wilt at either inoculum density. The wilt-tolerant cultivar Grant had mild wilt symptoms in most plants at moderate inoculum densities, and a tenfold increase in inoculum did not increase wilt ratings. CB3, however, had higher incidence and severity of Fusarium wilt symptoms at high inoculum densities, although 60% of the plants survived for 9 weeks.