Genetic diversity and antifungal activities of the genera Streptomyces and Nocardiopsis inhabiting agricultural fields of Tamil Nadu, India

Actinomycetes receives much attention as plant-beneficial bacteria due to their distinct morpho-physiological, plant growth promoting and antifungal properties. Among the actinomycetes, members of the genus Streptomyces are of specific interest due to their metabolic versatility and ubiquity. The diversity of Streptomyces in different crop fields of Tamil Nadu has not been explored early. In this study, we explored phylogenetic diversity, morphological heterogeneity, and antifungal properties of cultivable actinomycetes isolated from the rhizosphere and bulk soils of different crops collected from 20 distinct districts of Tamil Nadu. A total of 65 actinomycetes were isolated from 40 soil samples including rhizosphere and bulk soils of different crops, and their diversity was analyzed using the 16S rRNA gene sequence. They were then characterized for cultural characteristics and antifungal activity against four fungal strains Fusarium udum, Fusarium oxysporum f.sp. ciceri, Macrophomina phaseolina and Sclerotium rolfsii. Out of the 65 isolates sequenced, 45 were found to be closely related to Streptomyces spp. while the remaining 20 showed similarities with Nocardiopsis spp. Cultural characterization on four different ISP media showed immense diversity among the members of the genera Streptomyces and Nocardiopsis. The strains of Streptomyces spp. and Nocardiopsis spp. showed varying levels of antifungal activity with all strains found antagonistic against both Fusarium udum and Fusarium oxysporum f.sp. ciceris. All the strains obtained in this study have been accessioned at the National Agriculturally Important Microbial Culture Collection (NAIMCC) to increase the database of characterized strains belonging to these two genera in the collection.