Abstract

In this study, 30 bacterial strains isolated from marine biofilms were screened for their antifungal activity against Rhizoctonia solani by dual culture assay. Two bacterial strains, Bacillus subtilis and Bacillus cereus, showed a clear antagonism against R. solani on potato dextrose agar (PDA) medium. The antagonistic activity of B. subtilisagainst this pathogen persisted after one month of co-culture. An in vitro antagonistic assay using potato tuber slices was set up allowing both the screening of bacteria for their biocontrol proprieties and for their rotting effect on plant tissues. Potato tuber slices treated with B. cereus showed a heavy tissues rotting, probably due to the secretion of several enzymes. Whereas, B. subtilis did not show any tissues rotting on treated potato tuber slices. In addition, the potato tuber slices treated with B. subtilis and subsequently inoculated with R. solani agar culture showed a reduced fungal infection in comparison to the control tuber slices inoculated with the pathogen only. The crude extract of B. subtilis strain culture in Luria-Bertani  (LB) medium at 48 h of incubation showed a high antifungal activity against R. solani growth and no cytotoxic effect on Brine shrimp larvae.

Key words: Antagonism, Bacillus spp., biological control, black scurf of potato, marine biofilms.