EVALUATION OF BACTERIAL EPIPHYTES ISOLATED FROM AVOCADO LEAF AND FRUIT SURFACES FOR BIOCONTROL OF AVOCADO POSTHARVEST DISEASES

Bacteria isolated from Fuerte avocado leaf and fruit surfaces were evaluated for in vitro antagonism toward Dothiorella aromatica. Thirty-three bacteria exhibiting pronounced growth inhibition were further tested for antibiosis against Colletotrichum gloeosporioides, Thyronectria pseudotrichia, Phomopsis perseae, Pestalotiopsis versicolor; and Fusarium solani. Optimum disease-reducing concentrations of Bacillus subtilis (isolate B246) exhibiting the highest degree of antibiosis were determined according to a checkerboard-type titration assay, by artificial inoculations on Fuerte and Edranol avocado fruit in the laboratory. Various concentrations (10(5), 10(6), 10(7), and 10(8) cells ml(-1)) of B. subtilis were also incorporated into commercial Tag-wax and applied to Hass avocado fruit in the packinghouse for control of anthracnose, Dothiorella/Colletotrichum fruit rot complex (DCC), and stem-end rot (SE). In the artificial inoculation study, increasing concentrations of B. subtilis were effective against increasing concentrations of C. gloeosporioides, F. solani, and T. pseudotrichia. Control of D. aromatica was significant at the lower (10(3) and 10(4) cells ml(-1)) pathogen concentrations, whereas inhibition of P. perseae and P. versicolor was more readily achieved at the lower (10(5) and 10(6) cells ml(-1)) antagonist concentrations. In the packinghouse, a B. subtilis concentration of 10(7) cells ml(-1) significantly reduced anthracnose and SE externally and internally, while the lower B. subtilis concentrations (10(5) and 10(6) cells ml(-1)) were effective against internal DCC. Based on treatment means of all external and internal postharvest disease data, all B. subtilis concentrations performed equally well in controlling postharvest diseases.