Biological Control of Potato Isolate of Rhizoctonia solani by Streptomyces olivaceus Strain 115

This is the first report of antifungal activity of Iranian actinomycete isolates against Rhizoctonia solani Kuhn AG-3 (Teleomorph: Thanatephorus cucumeris [(Frank) Donk]). Biological control offers an environmentally friendly alternative to the use of antimicrobials for controlling plant diseases. A collection of about 200 actinomycete strains was screened for the ability to produce metabolites that inhibit R. solani growth in vitro. The Streptomyces olivaceus strain 115 showed strong in vitro antagonistic activity against R. solani in agar disc and Well-diffusion methods by producing extracellular antifungal metabolites. The strain No. 115 was propagated in submerged cultures and active crude was prepared upon which some biological characterization performed. The active metabolite(s) is polar, soluble in H2O and methanol but insoluble in chloroform, dichloromethane or hexane. Thermal inactivation point of active phase of S. olivaceus strain 115 was 80 C. Antifungal active phase of S. olivaceus strain 115 tolerate range of pH (6-9). Antifungal gene from strain 115 may be a useful candidate for genetic engineering of agriculturally important crop for increased tolerance against R. solani.