In Vitro Screening of Antagonistic Activity of Soil Streptomyces against Plant Pathogenic Fungi and Assessment of Its Characters

Actinobacteria from the genus Streptomyces have been studied as potential biocontrol agents worldwide. In this study, a total of 35 isolates of Actinomycete like colonies were isolated from the rhizospheres of various plant species. These isolates were primary screened for antagonistic activity to inhibit mycelial growth of Colletotrichum gloeosporioides. The screen revealed that seven isolates of Actinomycete like colonies were good inhibitors of the fungal mycelial growth and were chosen for their antagonistic effects against C. gloeosporioides and Biporalis maydis by the dual culture method. The isolate that had the best inhibitory effect on both fungi was further evaluated for antagonistic activity against C. capsici, Pyricularia sp., Fusarium sp., Curvularia sp. and Sclerotium roftsii. The results showed that the selected isolate inhibited the mycelial growth of C. capsici, Pyricularia sp., Fusarium sp. and Curvularia sp. within the range of 65.5-91.6%, while it did not affect the mycelial growth of S. roftsii. Moreover, the culture filtrate of the selected isolate inhibited the mycelial growth of C. gloeosporioides and B. maydis under in vitro condition. Based on the 16S rDNA gene sequence, colony morphology, spore chain rearrangement and physiology, the best isolate belonged to the genus Streptomyces and assigned as Streptomyces sp. isolate SRF1. These findings suggest that the Streptomyces sp. isolate SRF1 is a potential candidate, with a broad antagonistic activity, for use as a biocontrol against plant pathogenic fungi.