MICROFLORA ASSOCIATED WITH THE RHIZOSPHERE OF CALOTROPIS GIGANTEA

Abstract

The study of the rhizosphere of Calotropis gigantea revealed that during all Its stages of growth the microbial population in the rhizosphere was higher than that occurring in the control soil. The bacterial, actinomycetal and mould populations showed their individual characteristic variations proving that the rhizosphere, of each plant, is a special zone of microbial activity. These population changes were accompanied by a rhizosphere effect, the degree of which varied with the development of plant.

The high count of actinomycetes in the rhizosphcre, a factor -which led to this systematic study was established to be caused by a Nocardia sp. dependent upon glutamate for it's growth. This Nocardia sp. showed antibiotic activity against a culture of Saccharomyces cerevisiae and a yeast sp. flourishing well in the soil away from the rhizosphere influence. The reason(s) for this unusual association of a plant with a Nocardia sp. remains to be settled.

The HTPI method proved useful in the isolation of actinomycetes from the rhizosphere. It facilitated equally well in the isolation of the heat-resistant types (mostly spore formers) of microorganisms occurring in rhizosphere.

All the isolated actinomycetes strains were found to be pectinolytic.