Evaluation of bacillus subtilis as potential biocontrol agent for postharvest green mold control on 'Valencia' orange

Jiuxu Zhang, Huating Dou


Effective biocontrol of postharvest decay could provide an alternative approach for chemical control and for shipping chem-free citrus. Developing effective biocontrol agents, formulations and application methods for postharvest decay control of citrus is obviously needed. With the effort to look for effective biocontrol agents, two Bacillus subtilis strains GB03 and GB07, were tested for their potential biocontrol activity of green mold caused by Penicillium digitatum on 'Valencia' orange. B. subtilis strain GB07 achieved green mold control of 72.2 to 100% in four separate experiments when a preventive test method was used. GB03 only showed green mold control of 11.1 to 55.6% under the same test conditions. GB07 also reduced green mold incidence by 83% when it was applied to naturally infected fruit using a simulated commercial application system through a packingline. The performance of GB07 for green mold control was similar to that of standard chemical thiabendazole (TBZ) at 1,000 ppm level. To achieve good biocontrol activity, GB07 should be present in injury sites prior to P. digitatum infections. A minimum required concentration of GB07 at a 3×3 mm injury has been calculated as 2×10[sup6] cells. Under temperatures from 10, 15, 20, 25, and 30C, the best effect of GB07 on decay reduction was obtained at 30C, followed by 25C. GB07 has also been demonstrated to produce antifungal compounds which actively suppressed the growth of P. digitatum in vitro. B. subtilis GB07 may have good potential to be developed as a new biocontrol agent of green mold and other decays on Florida citrus fruit.


citrus; penicillium digitatum; postharvest decay; biological control

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283

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