CONTROL OF POSTHARVEST BROWN-ROT OF NECTARINES AND PEACHES BY PSEUDOMONAS SPECIES

Microbes were applied to nectarines and peaches to control postharvest brown rot caused by Monilinia fructicola. Two yeasts applied to wounds on fruit before inoculation protected fruit from subsequent infection, but they could not control decay when applied after inoculation. Two antibiotic-producing bacteria, Pseudomonas corrugata and P. cepacia, significantly reduced decay when applied up to 12 h after inoculation. P. corrugata controlled decay with fewer colony-forming units (c.f.u.) than P. cepacia; <10(4) c.f.u. per wound of P. corrugata controlled decay, whereas P. cepacia required greater-than-or-equal-to 10(5) c.f.u. per wound. Both antagonists grew rapidly in wounds but not on the intact surface of fruit. Washed cells controlled decay but filter-sterilized culture fluids did not. Both bacteria controlled the decay of wound-inoculated peaches better than thiabendazole, and P. corrugata was only slightly inferior to triforine. In tests employing very high inoculum densities of M. fructicola, both pseudomonads significantly reduced decay but were inferior to isolate B-3 of Bacillus subtilis. Decay was poorly controlled by the pseudomonads in tests with commercial fruit that was not artificially inoculated. Infections characteristic of commercially grown fruit were not accurately simulated by the artificial inoculation methods used to select antagonists. Revised strategies to control brown rot by microbial antagonists are discussed.