Plant root exudates are known to affect survival, reproduction and development of various microorganisms in soil through extremely complex phenomenon. Saprophytic and pathogenic activities such as competition and antibiosis of the root microflora are mediated by exudates. An analysis of the effect of different crop root exudates such as groundnut, castor, soybean, sunflower, maize, green gram, hybrid sorghum and resistant pigeon pea revealed high inhibitory effect on conidial germination and radial growth of fusarium udum. In contrast, the root exudates of local sorghum varieties had less influence on the radial growth of antagonistic fungi viz., Penicillium sp., Trichoderma sp. Aspergillus sp. in the increasing order (6.8, 9.8 and 10 per cent), in spite of promoting germination and radial growth of the wilt pathogen Fusarium udum. However, root exudates of some crops such as groundnut, cotton, hybrid sorghum and resistant pipeaonpea had stimulatory effect on antagonistic fungi such as Aspergillus sp. Pencillium sp. and Trichoderma sp. in the range of 39.8 to 47.5 per cent. Root exudates of cotton were, however, found to promote both the wilt pathogen, as well as antagonistic fungi. Groundnut and castor exudates were found to be at par with each other in the promotion of radial growth of antagonists. Identification of such biochemical compounds in the crop root exudates responsible for inhibition or stimulation of the fungi would be more useful.
