Antimicrobial and plant growth-promoting properties of the cacao endophyte Bacillus subtilis ALB629

Aims: To investigate the effects of the endophyte Bacillus subtilis ALB629 on the growth of cacao seedlings at early developmental stage and to evaluate its antimicrobial properties. Methods and Results: Germinating cacao seeds were inoculated with ALB629, and seedlings growth was evaluated 30 days later. Significant increase (P < 0.05) was observed in the root system (up to 30%), leaf area (14%) and stem height (7.6%). ALB629 colonized the entire plant, prevailing over indigenous micro-organisms. In addition, it was tested in vitro, by pairing assays, and showed antagonistic effect against the phytopathogenic fungi Moniliophthora perniciosa, Colletotrichum sp. and C.gossypii. When tested in cacao-grafting procedure in the field, ALB629 increased the grafting success rate (24%), indicating its protective effect. In addition, this Bacillus secretes an antagonist compound, as shown by the antifungal activity of the cell-free culture. Conclusions: Bacillus subtilis ALB629 promotes cacao root growth, besides promoting growth of the aerial part of cacao seedlings. It has antimicrobial properties and produces an antifungal compound. Significance and Impact of the Study: ALB629 presented beneficial characteristics for cacao cultivation, being a good biological control agent candidate. Furthermore, it is a potential source of antifungal compound with potential for commercial exploitation.