Development Of Biological Seed Coating Formulation For Control Of Bacterial Fruit Blotch

Bacterial fruit blotch(BFB)as a devastating bacterial seedbone disease,was caused by Acidovorax citrulli,which results in serious damage on leaves and fruits in many cucurbit crops,including Cucumis sativus,Citrullus lanatus and Cucumis melo.Along with spread over a long distance by contaminated seeds,pathogen of BFB is able to survive for decades in the seeds.Therefore,melon seed treatment is considered to be one of the most direct and effective measures in controlling this disease.Neither breeding of the disease resistant varieties nor traditional chemical control methods could solve this problem effectively and withdraw environmental pollution at the same time.Therefore,the applying of biological agents against BFB become the main direction of further research.As the gram positive bacteria,Bacillus sp.can resist a variety of adverse environment confitions and produce internal resistance spores.Its simple nutritional requirements,fast growing,convenience in storing and transport,safety to hygiene of humans and animals,can effectively prevent a variety of plant diseases and insects.Moreover,it is widely distributed in nature and considered to be a kind of ideal biocontrol organisms.To promote the biocontrol strategy of BFB,one Bacillus sp.strain TS86 was isolated from infected melon seeds with efficient biocontrol potential.In vitro dual-culture test showed that TS86 has strong antagonist inhibitory against to A.citrulli.It was also detected that TS86 was safe and effective to germinating of melon(Cucumis melo)and water melon(Citrullus lanatus)seeds.Furthermore,TS86 was used to prepare biological seed coating agent by using its fennentation 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(PVA)was selected as the optimal film former for its high good film forming ability,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 as the optimal warning coloration for if 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 is 4.0×108?5.0×108 CFU/mL,with weak acidity(pH value = 5.70)and the viscosity is 46 mPa·s.The bacterial concentration was 5.1×106CFU/mL after twelfth month storage represents TS86 could maintain high level concentration on 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 ta the dosage of 1:50 and biocontrol effectiveness of the biological seed agent.The results indicated that,the biocontrol efficacy against BFB in Cucumis melo and Citrullus lanatus were increased by 70.63%and 80.59%respectively.All together,we can conclude that the biological seed 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.