Effect of the host plant on the efficacy of Verticillium chlamydosporium as a biological control agent of root-knot nematodes at different nematode densities and fungal application rates

In general, increases in the density of Meloidogyne spp. in soil resulted in more nematodes in roots which, in turn, caused greater abundance of the nematophagous fungus, Verticillium chlamydosporium, in the rhizosphere of several plant species. At least 500 second-stage juveniles added to soil were required to stimulate fungal growth on the roots of kale and tomato plants. Plant species differed in their ability to support growth of the fungus in their rhizospheres at different nematode densities; fungal density increased more with increased nematode density on the roots of maize and tomato plants than on kale. Increasing the application rate of chlamydospores 10-fold resulted in increases in the density of the fungus in soil but not necessarily in the rhizosphere. Also, there was no simple relationship between the density of the fungus on roots and the proportion of eggs parasitised. In general, >90% eggs exposed in the rhizosphere were parasitised and application of the fungus caused significant reductions of three root-knot species, M. incognita, M. javanica and M. arenaria on maize, kale and Phaseolus. However, reductions of nematode infestations were much smaller if significant numbers of eggs remained within roots, a characteristic of nematode-susceptible plants such as tomatoes which develop large galls on infested roots. Knowledge of the plantʹs susceptibility to nematode attack and its ability to support the growth of V. chlamydosporium in its rhizosphere is essential for the development of biomanagement strategies based on the use of this fungus.