Identification Of Antagonistic Bacillus Against Astragalus Root Rot And Evaluation Of Their Application Potential As Biopesticides

This study was aimed at identifying antagonistic Bacillus G88?G11?G10 against Astragalus root rot and evaluating their application potential as biopesticides.Studies were made focusing on the classification status of the 3 antagonistic microorganisms and their plant growth promoting performance.Preliminary studies were made of the anti-fungi substances produced by strains G88 and G11.Besides,the fermentation media were optimized and the colonization ability,genetic stability and the compatibility between two antagonistic strains were measured.These studies lay the foundation for the follow-up development of biopesticides.The main results were as follows:1.Classical taxonomy including morphological,physiological and biochemical tests and 16 S rDNA gene sequence analysis were adopted in classifying and identifying strain G88,G10 and G11.The BBL CrystalTM was used to verify the identification result.Strain G88 was identified as Bacillus atrophaeus;strain G10 and G11 were identified as Bacillus subtilis.2.The test results of phosphate solubilization,potassium dissolution,nitrogen fixation,production of IAA,HCN and amylase showed that the three strains had good growth promoting effects.3.It was found that the type and activity of antifungi substances produced by strains G88 and G11 were different.The G88 had the ability to produce biofilm,but G11 did not.4.Using Fusarium solani as the target,the optimization of fermentation media of antagonistic Bacillus G88 and G11 was carried out by response surface methodology.The fermentation medium for strain G88 consists of glucose,21.16 g/L;beef jelly,17.31 g/L;peanut powder,20.64 g/L;CaCO3,2.0 g/L,and NaCl,0.7%.The fermentation for strain G11 consists of glucose,9.72 g/L;peptone,23.65 g/L;soybean meal,6.49 g/L,CaCO3 2.0 g/L;and FeSO4,0.0008%.The antifungi activity of the fermentation broth of strain G88 and G11 increased by 21.8% and 8.1% respectively when using the optimized fermentation medium.5.The strains G88 and G11 were labled with ampicillin to determine the soil colonization ability of G88 Ap and G11 Ap.The results showed that the two strains have the highest colonization ability on 7th day,reaching 1.18~1.73×106 cfu/g.After that,it gradually declined with time down to 1.0~1.35×105 cfu/g on 30 th day.Accordingly,antagonistic Bacillus can be applied every 20 days in order to maintain its number.6.The results of subculture showed that strains G88 and G11 have excellent genetic stability.The antifungi activities of the 10 th generation of the two strains had no significant difference from those of the original strains(P=0.05).The results of dual culture test showed good compatibility between strains G88 and G11,which provides a possibility for mixed application to increase the control effect.