Postharvest Biological Control of Stone Fruit Brown Rot byBacillus subtilis

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Abstract
Pseudomonas cepacia, P. fluorescens, Bacillus thuringiensis and 2 isolates of B. subtilis (B-3 and B-1849) were tested in the laboratory for antagonism against Monilinia fructicola on wounded stone fruit. Peaches, nectarines, apricots and plums were sprayed with bacterial suspensions, inoculated 1-2 h later with spores of M. fructicola, then held in moist chambers at 18-24.degree. C. Only the B-3 strain of B. subtilis controlled brown rot on all fruit types. When varying concentrations of B-3 were tested on peaches, brown rot development was retarded by 106 and 107 colony-forming units per milliliter. At 108, fruit did not become infected with M. fructicola but decayed after 9 days because of other fungi. Strain B-3 reduced decay regardless of the inoculum level or the isolate of M. fructicola tested and was effective at temperatures of 10-30.degree. C. The mechanism of B-3 activity appears to involve production of an antifungal substance, since the culture filtrate protected fruit from rot. The filtrate retained activity after being autoclaved at 15 psi and 120.degree. C for 15 min.