Control of postharvest diseases on citrus fruit by preharvest applications of biocontrol agent Pantoea agglomerans CPA-2 : Part II. Effectiveness of different cell formulations

Abstract

Infection of citrus fruit by postharvest pathogens often occurs in the field prior to harvest; therefore, it could be advantageous to apply biocontrol agents before harvest, which would reduce initial infection and then remain active and control pathogens in storage and under commercial conditions. The objective of the present work was to evaluate the effectiveness of different formulations of Pantoea agglomerans applied preharvest for controlling postharvest diseases on citrus. Results confirmed the protective effect of the additive Fungicover (FC) on populations of P. agglomerans exposed to non-conducive field conditions. In general, when osmotic-adapted and lyophilised P. agglomerans cells were used in bacterial treatments, these treatments showed greater survival rates than treatments with non-osmotic-adapted or fresh cells under field conditions. However, this superiority was only found when Fungicover was also added to suspensions of bacterial treatments. Therefore, bacterial treatments with Fungicover had population levels of P. agglomerans cells 1.2 and 2.8 log CFU cm −2 higher than bacterial treatments without Fungicover during field experiments. These results allowed us to conclude that it is possible to improve environmental stress tolerance and ecological competence of P. agglomerans cells by integrating certain formulation strategies. Consequently, the improved formulation of P. agglomerans provided an effective control for orange fruit against natural postharvest pathogen infections and artificial infections of Penicillium digitatum with values of decay reduction higher than 50%. These latter results also demonstrated that it is possible to control postharvest pathogens using bacterial preharvest treatments.