Mode of Action of Bacillus subtilis for Control of Avocado Post- harvest Pathogens

Bacillus subtilis (isolate B246), Bacillus cereus (isolate B247 and B249) and Bacillus licheniformis (isolate B248) were inhibitory to avocado post-harvest pathogens Colletotrichum gloeosporioides, Phomopsis perseae, Drechslera setariae, Pestalotiopsis versicolor and Fusarium solani; when tested with the dual culture technique. In vitro growth of Thyronectria pseudotrichia was not suppressed by any of the antagonists, while B. cereus isolate B247 did not inhibit growth of Dothiorella aromática. B. Cereus isolate B249 actually stimulated development of Lasiodiplodia theobromae. Diffusable metabolites from the four antagonists impeded growth of C. gloeosporioides, D.aromática, P. perseae, L. theobromae, but not of T. pseudotrichia. B. subtilis (B246) mode of action was determined using an in vitro spore-germination assay. In vitro the antagonist effectively reduced percentage spore germination of C. gloeosporioides, D. aromática, P. perseae, L. theobromae, F. solani, P. versicolor and D. setariae. In addition, bulb formation and lysis of hyphae were observed, as well as bacterial movement towards germinating spores and subsequent attachment to the spores. The possible mode of action of B. subtilis is discussed.