Abstract：Bacterial fruit blotch (BFB) caused by Acidovorax citrulli results in serious damage on leaves and fruits in many cucurbit crops. To promote the biocontrol strategy of BFB, one Bacillus sp. strain TS86 was isolated from infected melon seeds with efficient biocontrol potential in previous study. In vitro dual-culture test showed that TS86 had strong antagonist inhibitory against to A. citrulli. It was also detected that TS86 was safe and effective to seeds germinating of muskmelon (Cucumis melo) and water melon (Citrullus lanatus). Furthermore, TS86 was used to prepare biological seed coating agent by using its fermentation liquor as active ingredient, in order to accelerate the TS86 related product development and application. Seed coating agents screen test displayed 4% polyvinyl alcohol AH-26 was selected as the optimal film former for good film forming ability, water resistant property, water permeability, air permeability and swelling capacity, with no harm to biocontrol bacteria; 5% ethylene plycol was selected as the optimal antifreeze for its acceptable property of resistance to frost; 0.3% fuchsin acid was selected as the optimal warning coloration for it had batter boating color. In addition, 5% sucrose was added as the best combination. Consequently, biological seed coating agent was prepared by mixing the fermented liquid of biocontrol bacteria TS86 and various auxiliaries with a certain ratio. The determination of the indicators revealed the initial concentration of TS86 in seed coating agent was 4.0×108~5.0×108 CFU/mL, with weak acidity (pH 5.70) and the viscosity was 46 mPa/s. The bacteria concentration was 5.1×106 CFU/mL after storage for 1 year which suggested that TS86 could maintain high level concentration in room temperature for a long time. Greenhouse tests were carried out to evaluate the biocontrol efficacy of TS86, in which plant seeds with pathogen were pretreated with seeds coating at the dosage of 1∶50 and biocontrol effectiveness of the biological seed agent. The results indicated that, the biocontrol efficacy against BFB in watermelon and muskmelon were increased by 70.63% and 80.59%, respectively. All together, we could conclude that the biological coating agent which was created by TS86 was highly effective in BFB controlling during melon production. To the best of our knowledge, its characteristics of high efficiency, safety and environmental protection has a great significance in sustainable control of BFB and reduce of pesticide pollution.
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