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Biological Control of Multiple Plant Diseases and Plant Growth Promotion in the Presence of Pathogens by Plant Growth-Promoting Rhizobacteria (PGPR) 
K. LIU (1), J. W. Kloepper (1), J. A. McInroy (1), C. H. Hu (1). (1) Auburn University, Auburn, AL, U.S.A.

PGPR strains <i>Bacillus aerophilus</i> AP69 and <i>B. amyloliquefaciens</i> subsp. <i>plantarum</i> AP199, which previously demonstrated biological control of three different diseases in the growth chamber, were tested for both biological control of multiple plant diseases and plant growth promotion in the presence of pathogens in the greenhouse. Tests evaluated mixtures of AP69 and AP199, <i>B. amyloliquefaciens</i> subsp. <i>plantarum</i> strain GB03 was a positive control, a disease control, and a healthy control. The specific diseases tested in this study included bacterial spot of tomato (<i>Xanthomonas axonopodis</i> pv. <i>vesicatoria</i> (Xav)), bacterial speck of tomato (<i>Pseudomonas syringae</i> pv. <i>tomato</i> (Pst)), and damping-off of cucumber (<i>Pythium ultimum</i>). Results indicated that the two individual PGPR strains and their mixture significantly reduced severity of all three diseases compared to the disease control, and only the mixture significantly increased the root dry weight and four root morphology parameters in all three experiments while individual strains significantly increased some of these growth parameters. In the test of <i>P. ultimum</i>, AP199 and the mixture reduced disease severity and promoted plant growth better than GB03. Also in presence of Pst, plant growth of the mixture was equivalent or higher than the healthy control.

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