Culturable bacteria from plum fruit surfaces and their potential for controlling brown rot after harvest

Fruit microflora have been the richest source of antagonists against fruit decays and the active ingredient in all currently available commercial biocontrol products. A comprehensive evaluation of plum bacteria for biocontrol activity against Monilinia fructicola, which causes brown rot of stone fruit, is important for determining their biocontrol potential. Resident culturable bacterial microflora of plums from early fruit development until maturity were characterized. The most dominant genera were Curtobacterium (19.88%), Pseudomonas (15.06%), Microbacterium (13.86%), and Clavibacter (12.65%). These genera occurred at all four isolation times and accounted for 61.45% of all isolates. Microbacterium and Curtobacterium dominated at the early stage of fruit development while Pseudomonas and Clavibacter were dominant at the end of the season. Less prevalent genera were Enterobacter (5.42%), Chrysomonas (4.82%), and Pantoea (4.22%). Most frequently isolated species were Microbacterium lacticum, Clavibacter michiganensis, Curtobacterium flaccumfaciens, Enterobacter intermedius, and Chrysomonas luteola. The seasonal succession of genera was observed in both MANOVA and frequency analysis. Primary and secondary screening of plum-inhabiting bacteria for control of brown rot on wounded fruit resulted in selection of several antagonists among which Pantonea agglomerans and Citrobacter freundii were the most effective. These antagonists grew well in plum wounds and increased by four log units during first three days at 24 °C, and two log units after seven days at 4 °C. Results indicate that plum microflora are an excellent source of antagonists against brown rot decay originating from wounds after harvest.