Biological control of postharvest diseases of peach with phyllosphere isolates ofPseudomonas syringae

Commercially ripe peaches were wounded and co-inoculated with phylloplane isolates of Pseudomonas syringae (MA-4 and NSA-6), Pseudomonas fluorescens (BAP-3), or an isolate of Candida sp. (NSD-4) in combination with either conidia of Monilinia fructicola (cause of brown rot) or sporangiospores of Rhizopus stolonifer (cause of rhizopus rot). Isolates NSA-6 and MA-4 at a concentration of 1 x 107 CFU/mL reduced brown rot to 28% and 73%, respectively, from 98% in the inoculated check after 5 days incubation at 22°C. Both isolates reduced rhizopus rot to 5% and 8% from 53% in the inoculated check after 5 days incubation. The P. syringae isolates when used in 2-min soak treatments were less effective against natural, preharvest M. fructicola infections of late-harvested peaches. Isolates MA-4 and NSA-6 suppressed brown rot from 63% to 30% and from 95% to 71-81%, respectively, after 3 and 4 days incubation at 22°C. The use of 0.5% CaCl2 in the soak suspension significantly improved the activity of P. syringae but the use of “peach wax” (Decco 282) increased brown rot incidence and negated the beneficial effect of CaCl2.