Screening,Identification,Optimization Of Culture Conditions And Bacteriostasis Of Antagonistic Bacteria Againest Phytophthora Capsici

Phytophthora capsici is a soil borne disease caused by Phytophthora capsici,which mainly affects the stems,leaves and fruits of capsicum,and can cause wilting,defoliation and fruit decay after infection.Once the disease spread rapidly,pose a great threat to the production of pepper,often caused by a reduction of 20% to 30%,and even cause damage to farm crops,seriously affect the yield and quality of pepper.At present,the main production by metalaxyl,cymoxanil and other systemic chemical fungicides to control Phytophthora,but on the use of the systemic fungicide is easy to produce drug resistance,and also control measures based chemical control of pharmaceutical residues and environmental pollution etc..Therefore,the biological control of Pepper Blight is the inevitable choice for the sustainable development of the current pepper production.1.This study isolated from 43 soil samples in Hainan purification screened bacterial strains A1~A73 73 strains had antagonistic effect on Phytophthora capsici,after a series of antibacterial experiments showed that A60 was the highest antibacterial activity,antibacterial circle radius of Phytophthora capsici is up to 11.63 mm,the inhibitory effect of cultured after stability.Through physiological and biochemical characteristics,16 S rDNA sequence and phylogenetic tree analysis,it can be concluded that the antagonistic bacteria A60 strain is Brevibacillus laterosporus.2.A preliminary study was conducted on the antibacterial substances of the antagonist A60.The results showed that the antibacterial substances were water-soluble and mainly existed in the supernatant of the fermentation broth and were extracellular secondary metabolites.Its antibacterial effect in different parts of fermentation broth: whole broth> supernatant> bacterial suspension> cell disrupting liquid.The bacteriostatic effect of fermentation broth of different implementation multiples on Phytophthora capsici strains: The inhibition rate of 10-fold diluted fermentation broth can reach 78.7%,and the inhibition rate of 20-fold dilution is 62.8%.A small amount of volatile substances in the antagonistic A60 fermentation broth had a certain inhibitory effect on the mycelium growth of Phytophthora capsici.A60 has obvious inhibitory effects on pathogens such as Phytophthora capsici,tomato early blight,tomato gray mold,pepper anthracnose,and pear black spot.3.In order to improve the antagonistic effect of A60 fermentation products of Phytophthora capsici and its fermentation medium composition and fermentation conditions were optimized: first screening to determine the optimum carbon source,nitrogen source and inorganic salt B.laterosporus A60,on the basis of orthogonal concentration of soluble starch,yeast powder and sodium chloride on the optimization design method.The culture temperature,pH,inoculum,liquid volume and other factors on B.laterosporus inhibitory activity of A60,and ultimately determine the optimal fermentation medium and fermentation conditions of Brevibacillus laterosporus A60 soluble starch 1%,yeast powder 2%,sodium chloride 0.2%,initial pH was 7,2% inoculation quantity,load 100mL/250 mL flask,fermentation temperature is 37℃.4.Phytophthora capsici occurred on Capsicum and sweet pepper.This experiment was conducted on pepper and sweet pepper by using the sterile fermentation liquid of antagonistic bacteria A60 with good antibacterial effect.Experimental results show that the addition of antagonistic bacteria A60 fermentation filtrate of pepper in the 3D without the disease,control effect can reach 100%,5D 95.71%,7d still reached 92.22%,indicating antagonistic A60 can reduce the incidence and disease index significantly,and has a very good effect.Join the antagonistic bacteria A60 fermentation filtrate of sweet pepper,at 3D without the disease,control effect can reach 100%,5D 75.26%,7d still reached 73.20%,indicating antagonistic A60 can reduce the incidence and disease index significantly,and has the effect to better control effect,but the effect on sweet pepper than on pepper slightly worse,when used should be appropriate to increase the concentration of.