Enhancement of Rotylenchulus reniformis suppressiveness by Crotalaria juncea amendment in pineapple soils

The abilities of sunn hemp, Crotalaria juncea amendment to enhance Rotylenchulus reniformis suppressiveness were tested in soils collected from six pineapple fields with different length of time after nematicides 1,3-dichloropropene application, and after pineapple planting. Soils were frozen to kill the indigenous nematodes, then either amended or not amended with chopped C. juncea tissues and infested with 1000 R. reniformis in a greenhouse experiment. Cowpeas were grown in these soils for 6 weeks. Amendment enhanced the population density of nematode-trapping fungi (NTF), the percentage of eggs parasitized by fungi, and the bacterivorous nematodes. Enhancement of NTF was highest in soils that had least been treated with 1,3-dichloropropene and in soils planted with pineapple for the longest period of time. NTF can also be enhanced by C. juncea in soils that had been fallowed without nematicides treatment. The suppression on R. reniformis eggs was correlated with the enhancement of NTF (r = 0.65, P < 0.01), and with that of the percentage of eggs parasitized by fungi (r = 0.61, P < 0.01). The suppressive effect of vermiform R. reniformis in the rhizosphere was correlated with the bacterivorous ne-matodes enhancement (r = 0.68, P < 0.01). The effect of C. juncea on R. reniformis suppression was not pronounced and was not reflected in cowpea plant growth