Identification of Antifungal Substance (Iturin A2) Produced by Bacillus subtilis B47 and Its Effect on Southern Corn Leaf Blight

Abstract

Bacillus subtilis B47 is an endophytic bacterium of tomato, and produces substance that strongly inhibits the growth of Bipolaris maydis, the pathogen of southern corn leaf blight (SCLB), as well as several other phytopathogenic fungi. The antifungal substance was purified from the broth culture of the bacterium using acid precipitation, methanol extraction, and three-step chromatography. Based on FT-IR spectrometry, amino acid composition, and MALDI-TOF-MS/MS CID analyses, the antifungal substance was identified as iturin A2, a cyclic lipopeptide antibiotic. To evaluate the efficacy of iturin A2 for control of SCLB, partially purified iturin A2 (75%, w/v) was applied under different conditions. At the concentration of 300 mg kg-1, iturin A2 showed efficacy ranging from 100 to 53.1% under in vitro, in plot and in field conditions. This efficacy was higher than or similar to that of the fungicide chlorothalonil. When the concentration of iturin A2 was increased to 500 mg kg-1, the control efficacy was enhanced to 64.2% in field, which was significantly higher than that of chlorothalonil. These results indicate that iturin A2 has potential for SCLB control and could be a substitute to synthetic fungicides. To our knowledge, this is the first report on using partially purified iturin A for control of SCLB under field conditions.