SUPPRESSION OF ROTYLENCHULUS RENIFORMIS BY CROTALARIA JUNCEA , BRASSICA NAPUS , AND TAGETES ERECTA

The effects of Crotalaria juncea , Brassica napus and Tagetes erecta on resistance, allelopathic suppression, and enhancement of nematode antagonists against Rotylenchulus reniformis were examined in a series of greenhouse experiments. Crotalaria juncea and B. napus are poor hosts to R. reniformis as compared to Vigna unguiculata . Tagetes erecta was as good a host for R. reniformis as was Ananas comosus. Crotalaria juncea delayed the development of female nematodes compared to V. unguiculata . Allelopathic effects against R. reniformis were most pronounced in leaf leachate of C. juncea 2 days after incorporation where the viability of the nematode was suppressed to 0.5% as opposed to 60% when the R . reniformis were incubated overnight in leachates of B. napus , T. erecta , A. comosus , sand or distilled water. Amendment with C. juncea was most efficient in enhancing parasitic nematode-trapping fungi, R. reniformis egg-parasitic fungi, vermiform stage parasites, and bacterivorous nematodes compared to B. napus, and T. erecta leaf amendments. Bare soil and 1,3-Dichloropropene treatments suppressed nematode-trapping fungal population densities. Suppression of R. reniformis development on V . unguiculata by these crop amendments was inconclusive due to the short cowpea bioassay period. However, C. juncea amendments enhanced cowpea growth more than did the other soil amendment treatments. Among the crops tested, C. juncea is the most promising cover crop for R. reniformis management.