Bacterialfruit blotch (BFB) was a serious threatto cucurbitaceae crops. It was caused by the gram-negative
bacterium Acidovorax avenae subsp. citrulli. Two hundred strains, which have the potential in controlling
plant diseases in our laboratory’s biocontrol strain library, were employed to this research to screen some
antagonistic bacteria, which can efficiently control bacterial fruit blotch disease. Based on the results of
antagonistic activity experiments, greenhouse tests and field trials, 5 of the test strains have high abilities
to control BFB. One of the 5 bacteria strains has the highest potential to control BFB named 54. The
biocontrol efficacy of 54 was up to 60%. To characterize the strain, we used series of methods to evaluate
the bacterium, including morphology analysis, physiological biochemical test and biomolecular assay.
We found that the bacterium 54 belongs to the species Bacillus amyloliquefaciens. The colonization test
results showed that 54 had the highest colonization levels, and the density of the strain on leaves was up
105 colony forming units (CFU) per gram of leaftissue. Our recent results show that B. amyloliquefaciens 54
can promote the plant growth due to raised the contents of available N, P, K and the leaf chlorophyll. The
antagonistic bacterium 54 can significantly control the BF B by increasing the expression level of defenserelated
gene PR1 and the accumulation the hydrogen peroxide in the plant. The results oftrail experiment
was also verified this efficient results of bacterium. This is also the first report of B. amyloliquefaciens strain
that is able to control BFB.