Fungicidal activity of marine actinomycetes against phytopathogenic fungi

Abstract

A total of 160 isolates of marine actinomycetes were isolated from the sediment samples drawn from mangroves, estuary, sand dune, and industrially polluted coast. Of these, mangrove sediments were rich sources of marine actinomycetes. Each isolate was tested against four phytopathogenic fungi<i style="">,</i> <i style="">viz. Rhizoctonia solani,</i> <i style="">Pyricularia oryzae</i>, <i style="">Helminthosporium oryzae</i> (causing sheath blight, blast and leaf spot diseases of rice) and <i style="">Colletotrichum falcatum</i> (causing red rot disease of sugar cane). About 51% of isolates were found effective against <i style="">H. oryzae</i> and <i style="">P. oryzae</i>, 31% against <i style="">R. solani</i>, and 12.5% against <i style="">C. falcatum.</i> Of 160 isolates, 10 showed a potent activity against all the fungi tested. These isolates appeared to produce high antifungal compounds at 120 hrs of incubation period of production medium culture. Glucose and soybean meal were the best carbon and nitrogen sources, respectively and 17.5 ppt was the best salinity level for maximum antibiotic production. Cylinder plate method was found better for antifungal assay than the disc diffusion method. Based on the morphological and culture characteristics, the potent strains were identified as the species belonged to the genus <i style="">Streptomyces</i>. These strains may prove to be the potent source for isolation of agrobased fungicides.