Screening of Bacillus spp. as potential biocontrol agents against sunflower pathogens

Abstract

Bacillus spp. are well known to protect plants from seed or soil-borne pathogens by the synthesis of various metabolites with antimicrobial activity, such as hy?drolytic enzymes and antibiotics. This study aimed to select the most effective Bacillus spp. from a group of ten antagonistic strains by antifungal activity assay. Bacillus strains were primarily isolated from the soil and identified as B. safensis, B. pumilus and B. subtilis by 16S rDNA sequencing. The four analyzed fungi: Macrophomina phaseolina, Alternaria alternata, Cladosporium cladosporoides, and Sclerotinia sclerotiorum, were obtained from sunflower seeds and identified using PCR analysis and primers specific for ITS region. The antifungal activity of bacterial strains was examined in a dual plate assay. Bacillus spp. demonstrated the highest antagonism against S. sclerotiorum, followed by C. cladosporoides, M. phaseolina, and A. alternata, with an average percentage of growth inhibition (PGI) of 77%, 70%, 64% and 59%, respectively. Overall, Bacillus spp. included in this study demonstrated a rather strong biocontrol potential, although the effect of particular strain varied depending on the tested fungi. The highest antagonistic effect toward M. phaseolina and A. alternata was exhibited by B. safensis B2 and B. pumilus B3. B. pumilus B11 and B. subtilis B32 were the most efficient against C. cladosporoides, whereas B. pumilus B3 and B. subtilis B7 had the highest antifungal activity against S. sclerotiorum. Findings point to the fact that the most effective Bacillus spp. could be used as potential biocontrol agents for improving plant health and productivity.