Pilot Tests for Commercial Production and Application of Bacillus subtilis (B-3) for Postharvest Control of Peach Brown Rot

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Abstract
The potential of Bacillus subtilis for postharvest control of peach brown rot caused by Monilinia fructicola was assessed in pilot tests on simulated commercial packing lines at Bryon, GA, and Clemson, SC, and in a commercial packinghouse in Musella, GA. Because disease pressure was low due to drought conditions (1986), inoculum was introduced either in the dump tank water or as a spray onto the fruit after treatment on the line. Strain B-3 of B. subtilis was cultured in nutrient-yeast-dextrose broth (NYDB) in flasks at Byron or in another medium contained in a 250-L fermentor at Brownsville, TX. Nutrient broth was replaced by cottonseed flour as the primary source of nitrogen in the fermentor. This medium was low in cost, suitable for commercial use, and yet supported antibiotic production in culture, as did NYDB. In packing line tests, the number of colony-forming units of the bacterium added to each fruits was between 2 .times. 107 and 7 .times. 107 for B-3 from flask cultures and approximately 2 .times. 109 for B-3 from the fermentor culture. In a test at Byron, B-3, cultured in flasks and applied fresh or after being stored (as paste or powder), was equal to benomyl (1-2 ppm residue in fruit) for brown rot control. In a similar test at Clemson, stored forms of B-3 from both flask and fermentor cultures were as effective as benomyl. In the packinghouse, B-3 produced at Byron approached benomyl for disease control, whereas that produced in the fermentor had no effect. However, an inability to completely remove fungicide residues from equipment in the packinghouse and the need to spray-inoculate fruit twice with the pathogen introduced unusual circumstances.