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 eva luated for in vitro antagonism toward Dothiorella aromatica. Thirty-th ree bacteria exhibiting pronounced growth inhibition were further test ed for antibiosis against Colletotrichum gloeosporioides, Thyronectria pseudotrichia, Phomopsis perseae, Pestalotiopsis versicolor; and Fusa rium solani. Optimum disease-reducing concentrations of Bacillus subti lis (isolate B246) exhibiting the highest degree of antibiosis were de termined according to a checkerboard-type titration assay, by artifici al 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 appl ied to Hass avocado fruit in the packinghouse for control of anthracno se, Dothiorella/Colletotrichum fruit rot complex (DCC), and stem-end r ot (SE). In the artificial inoculation study, increasing concentration s of B. subtilis were effective against increasing concentrations of C . gloeosporioides, F. solani, and T. pseudotrichia. Control of D. arom atica was significant at the lower (10(3) and 10(4) cells ml(-1)) path ogen concentrations, whereas inhibition of P. perseae and P. versicolo r was more readily achieved at the lower (10(5) and 10(6) cells ml(-1) ) antagonist concentrations. In the packinghouse, a B. subtilis concen tration 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. B ased on treatment means of all external and internal postharvest disea se data, all B. subtilis concentrations performed equally well in cont rolling postharvest diseases.