Antifungal compounds as a mechanism to control Hemileia vastatrix by antagonistic bacteria

Abstract

Pseudomonas putida P286 and Bacillus thuringiensis B157 controlled coffee rust under greenhouse and field conditions. Now we studied the mechanism(s) of antagonism of both bacteria to Hemileia vastatrix. Bacterial effects on urediniospore germination and disease severity were evaluated in experiments with six treatments: (i) growth broth, (ii) supernatant centrifugation, (iii) bacterial cell centrifugation and re-suspension, (iv) UV inactivation of the bacteria, (v) 523 medium, and (vi) saline solution. The treatments i to iii reduced both spore germination and disease severity. Each isolate was applied at different concentrations and time periods before inoculation of H. vastatrix. The efficiency in controlling rust was reduced at the lowest concentrations and at the largest intervals between applications. In spatial separation experiments, both bacteria did not induce systemic protection, whereas protected locally the coffee plants against H. vastatrix. Therefore, the mechanism of both isolates against H. vastatrix is attributed to the production of antifungal compound (s).