Suppression of green and blue mold in postharvest mandarin fruit by treatment of Pantoea agglomerans 59-4

In order to control postharvest spoilage of satsuma mandarin fruits, rhizobacteria were isolated from soil samples. The Pantoea agglomerans strain 59-4 (Pa 59-4) which suppresses the decay of mandarin fruit by green and blue mold, was tested for the control efficacy and its mode of action was investigated. Pa 59-4 inhibited infection by green and blue mold on wounded mandarins, which were artificially inoculated with a spore suspension of Penicillium digitatum and P. italicum with control efficacies of 85-90% and 75-80%, respectively. The biocontrol efficacy was increased by raising the concentration of cells to between 10⁸ and 10⁹ cfu/ml, and pretreatment with the antagonist prevented subsequent infection by green mold. The population of Pa 59-4 was increased more than 10 fold during the 24 hr incubation at 20°C, indicating that colonization of the wound site might prevent the infection by green mold. Despite poor antifungal activity, the Pa 59-4 isolate completely inhibited the germination and growth of P. digitatum spores at 1 × 10⁸ cfu/ml. We argue that the control efficacy was mediated by nutrient competition. Overall, the effective rhizobacterium, Pa 59-4, was shown to be a promising biocontrol agent for the postharvest spoilage of mandarin fruits by green and blue mold.