Influence of seed and root exudations on the rhizosphere effect in Sorghum vulgare and Crotalaria juncea.

The influence of seed and root exudations on the rhizosphere effect of Sorghum vulgare and Crotalaria juncea was examined. While the quantitative occurrence of certain morphological and physiological groups of bacteria on the seeds and rhizospheres of the two plant species differed, there were similarities in the occurrence of certain physiological and nutritional groups of bacteria on the seed as well as on the rhizosphere. The occurrence of some genera of fungi on the seeds and in the rhizosphere indicated the influence of both seeds and root exudations on the rhizosphere effect. Increase in root exudations of amino acids and sugars correlated with a concomitant increase in microbial activity in the rhizosphere on the 15th day of growth in both plant species but there was a delayed effect of the exuded chemicals on the rhizosphere microflora after 30 d of plant growth.