Defense-related gene expression in response to the application of biological control agents in banana

Black Sigatoka, caused by P. fijiensis, is the most important banana disease in Latin America as increasing applications of chemical fungicides used for its management result in both higher banana production costs and pathogen resistance. Spores of Bacillus subtilis, a proprietary Trichoderma sp., and a biological fermentation product composed of Saccharomyces cerevisiae cell walls and copper sulfate, were applied separately to evaluate potential defense responses in banana plants. The leaves were artificially inoculated with the pathogen, and the biological control agents were applied to the soil to avoid direct antagonism with the pathogen. Significantly lower (P < 0.05) area under disease progress curve values were observed among all treated plants compared with the control, with the lowest value measured in the treatment with a 5 % (w/v) concentration of a yeast cell wall product. In a second trial, the same biological control agents were applied to banana plants at 5 % (w/v) concentration to determine the relative expression of defense-related genes. Higher relative expression (P < 0.05) of PR3 and PR9 was observed at 3 and 24 h after application in the plants treated with B. subtilis and Trichoderma sp., respectively. In the plants treated with the yeast cell wall product, higher relative expression (P < 0.05) of PR3 was measured 48 h after application. The findings indicate that plant defenses may be activated by the biological control agents.