Efficacy of Bacillus spp. to biocontrol of anthracnose and enhance plant growth on Andean lupin seeds by lipopeptide production

Abstract Anthracnose, caused by Colletotrichum acutatum , is the major fungal disease of Andean lupin ( Lupinus mutabilis ). The primary infection point is contaminated seed. The objective of this study was to evaluate four Bacillus strains with demonstrated abilities to control anthracnose on lupin seed to elucidate its mechanisms of antifungal activity. First, antifungal activity assays using living cells and cell-free compounds showed a strong ability to inhibit mycelial growth and conidial germination of C. acutatum . Based on these results, the two Bacillus strains that showed the highest antifungal activities were further screened for lipopeptide identification and the presence of lipopeptide genes. Thin layer chromatography (TLC) of butanolic extracts from cell-free compounds showed that both Bacillus strains produced antifungal lipopeptides, indicating that antibiosis could be a major factor involved in its biological control ability. TLC-bioautography analyses confirmed the presence of fengycin, iturin and surfactin lipopeptides and suggested that the strong antifungal activity could be associated only with fengycin lipopeptides. PCR amplification of the lipopeptide genes also displayed the presence of fengycin E, iturin B and surfactin B genes responsible for the antifungal activity of both strains. Bacteria treatments and cell-free compounds significantly reduced anthracnose incidence from 94% to 0% (untreated control). Seedlings grown from Bacillus treated seeds showed an increment in chlorophyll and protein contents, as well as in defence enzymes peroxidase and catalase, in comparison with seedlings grown from untreated control. These results suggest that Bacillus spp. strains are potential agents to control anthracnose infection on Andean lupin seed mediated by lipopeptide production, and they positively affect physiological processes and overall growth of lupin seedlings.