Bioprospecting of culturable actinobacteria from soil and rhizosphere as potential inhibitors of Sclerotinia sclerotiorum.

White mold, caused by S. sclerotiorum, is one important disease of soybean crops (Glicyne Max. (L)Merrill.) with considerable yield losses. Absence of effective control and resistance of the fungus to commercial fungicides make this phytopathogen a serious problem in tropical regions. Streptomyces species turn out to be potential candidates for agricultural applications due to their biotechnological features. The goal of this research was bioprospecting Streptomyces sp. for biocontrol of white mold. In order to evaluate the antifungal activity, six pre-selected isolates: S. rishiriensis (3AS4), S. albolungus (3BS4), S. champavatti (CanV2 39), S. violascens (CanV2 06f) and S. covourensis (1AS2a, 1AS2c) were used. They were grown for 2 weeks at 28 ºC at 135 rpm and crude extracts were obtained with Ethyl acetate (EtOAc) and Dichloromethane (DCM). Minimum inhibitory concentration (MIC) and spent media were performed against S. sclerotiorum. Biocontrol was evaluated under greenhouse conditions with inoculated nonsterile soil. The best MIC was determined as 0,165 mg.mL-1 for 1AS2a DCM extract. 3BS4 showed the highest mycelial inhibition growth (85,94%). Isolates 3AS4, 3BS4, 1AS2a and 1AS2c were capable of controlling white mold symptoms under greenhouse conditions. Regarding plant growth promotion, 1AS2a displayed the highest shoot:root ratio. These results suggest actinobacteria can be used as a potent biological control agent against white mold