CONTROL OF GREEN MOLD OF LEMONS WITH PSEUDOMONAS SPECIES

Applications of Pseudomonas cepacia reduced postharvest green mold (Penicillium digitatum) by more than 80% in lemon fruit (Citrus limon) compared with controls. The bacterium grew rapidly in wounds and caused no visible injury to the fruit. Decay was controlled if P. cepacia was applied within 12 hr or less after inoculation. The fungicides imazalil and thiabendazole were better eradicants; they were effective when applied 24 hr after inoculation. Other pseudomonads were not as effective as P. cepacia. Inhibition of fungal growth in vitro by P. cepacia reportedly is caused by the antibiotic pyrrolnitrin. Spores of P. digitatum did not germinate in potato-dextrose broth amended with 0.1-mu-g/ml pyrrolnitrin. However, decay caused by pyrrolnitrin-resistant mutants of P. digitatum, which could germinate in pyrrolnitrin at 60-mu-g/ml, was controlled by P. cepacia. Washed, viable cells of P. cepacia and P. corrugata reduced decay whereas cell-free culture fluids did not. P. fluorescens did not inhibit P. digitatum growth in vitro yet it reduced decay by about 70%. Antibiotics may not comprise the entire mode of action of pseudomonads on citrus.