A study was conducted to determine the effects of pre-harvest application of a bacterial antagonist, Burkholderia spinosa on the population dynamics of epiphytic and pathogenic microorganisms dwelling on banana (Musa spp.) leaves together with the population build-up of the applied bacterial antagonist. Banana cultivar Kolikuttu was established as an outdoor plot experiment and the antagonist was applied by two methods (i.e. a foliar spray and a soil drench) at nine times (i.e. 300 ml per plant per time) repeatedly at weekly intervals. Effects of leaf washings of plants treated with different application methods on germination of C. musae, the causal organism of several postharvest diseases of banana, spores were investigated in vitro. There was a significant (p<0.0001) interaction effect between time and method of B. spinosa application on the density of the bacterial antagonist on banana leaves. A gradual build-up of B. spinosa was observed on leaves with a peak density at 228 days after planting when bacterial antagonist was applied as a foliar spray. Burkholderia spinosa was not found on leaves of banana when the plants were treated as a soil drench or left untreated with the antagonist. Densities of Aspergilus spp. And unidentified fungal species on leaves of banana were significantly influenced by the method of application of B. spinosa. In contrast, density of Fusarium spp. on the banana phyllosphere varied significantly with the time of application (p<0.001). The density of yeast and unidentified bacterial species on banana leaves was not significantly influenced by the time and method of application or their interaction effect. Application of B. spinosa as a soil drench could reduce phyllosphere pathogens, Aspergillus spp. and Fusarium spp. Percentage germination of C. musae spores continued to increase 24 h after incubation in the leaf washing of control banana plants. In contrast, leaf washings of B. spinosa treated plants showed a decline in the percentage spore germination. The findings of the present study revealed the ability of B. spinosa for building up considerable cell densities on the treated leaf surface and its ability for suppressing a range of microbes. These are desirable features of B. spinosa to be used in field application for the control of foliar pathogens of banana.
Tropical Agricultural Research Vol. 25 (4): 543 – 554 (2014)