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Optimization of Bacillus amyloliquefaciens BAC03 Application in Controlling Streptomyces scabies
H. JIANG (1), Q. Meng (2), J. Hao (3). (1) Univ of Maine, Orono, ME, U.S.A.; (2) Univ of Maine, Spencer, IA, U.S.A.; (3) Univ of Maine, orono, ME, U.S.A.

<i>Bacillus amyloliquefaciens</i> strain BAC03 is a novel bacterial strain that had previously been studied for biological control of <i>Streptomyces scabies</i>. In order to optimize its efficacy, various application strategies were investigated for their effects on scab in radish and potato. Assessments included application using foliar spray, seed treatment, or potting-mix treatment. Tests were conducted with different timing, frequency, and concentrations of BAC03 in potting mix that was infested with <i>S. scabies</i>. Results showed that foliar application and seed treatment with BAC03 did not affect the disease severity in either radish or potato. BAC03 applied 5 days before planting completely suppressed (<i>P</i> < 0.05) radish scab, but the efficacy decreased as BAC03 application was postponed (<i>P</i> < 0.05). BAC03 at 10<sup>5</sup> CFU cm<sup>-3</sup> potting mix or higher concentrations (up to 5 ×10<sup>6</sup> CFU cm<sup>-3</sup>) was effective (<i>P</i> < 0.05) at reducing severity of radish scab. Increasing the frequency of BAC03 application did not increase efficacy for disease reduction. In addition, BAC03 increased (<i>P</i> < 0.05) the biomass of radish roots and leaves in the presence of the pathogen. The above results were confirmed by quantitative polymerase chain reaction that when BAC03 was applied before radish planting, the population of <i>S. scabies</i> was significantly lower (<i>P</i> < 0.5) than that in other BAC03 treatments at later stages.

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