Study On The Effect Of The Actinomycetes Strain LG-9 On The Control Of Verticillium Wilt In Cotton

Cotton verticillium wilt is prevalent in cotton planting areas of China,which seriously affects the sustainable development of cotton industry.An actinomycete strain LG-9 with significant inhibitory effect on cotton verticillium wilt was obtained in our laboratory,and its control effect on cotton verticillium wilt was explored.Objectives:Strain LG-9 was used as experimental material to study the preparation of solid bacterial agent,the effect of strain LG-9 on sclerotia of Verticillium dahliae was determined,objective to explore the feasibility of controlling verticillium wilt of cotton with biocontrol bacteria.Methods:Single factor design was used to screen the best solid-state fermentation medium formula and optimize the solid-state fermentation conditions of strain LG-9;The antagonistic effect between biocontrol strain LG-9 and the Sclerotinia formed by Verticillium dahliae was determined by mycelial growth rate method,inhibition of micro sclerotinia germination method and in vivo inoculation of cotton seedlings;The biological control effect of solid bacterial agent was determined by pot experiment of cotton,and the dosage and application period of solid bacterial agent were determined.Results:The solid fermentation medium formula of biocontrol bacteria LG-9 was determined as follows:every 100g millet was used as solid fermentation substrate,5.0%sucrose,6.0%peptone,1.5% CaCl₂,inoculum volume 15.0%,and initial water content 60%,the culture temperature was 28°C and the fermentation time was 9 days,the cell content reached 1.52×10⁸cfu/g.Actinomycete LG-9 could inhibit the mycelial growth and the formation of micro sclerotia of Verticillium dahliae;the germinating rate of sclerotinia was 0 after being treated with the sterile filtrate of strain LG-9 for 150 min;the original solution of sterile filtrate and strain LG-9 could inhibit the infection of cotton seedlings with the mycelium.When the dosage of solid bacterial agent was 0.5%～1%,it had certain control effect on verticillium wilt,and did not affect the growth of cotton seedlings;the biological control effect reached 100% when the dosage of solid bacterial agent was 5%,10% and 15%,which could increase the number of leaves,plant height and stem diameter of cotton seedlings,but the germination rate of cotton seedlings would be reduced when the dosage of bacterial agents was more than 10%.Using 5%inoculants to cultivate cotton seedlings can reduce the incidence rate of verticillium wilt,and the control effect is 100%.The number of leaves,height and stem diameter of cotton seedlings are significantly promoted.Inoculation of verticillium and actinomycetes solid inoculum reduces the incidence rate by 55.56%compared with the control.First,the spores suspension of Verticillium dahliae is applied,and 5% actinomycetes solid inoculants are applied to 5days after the treatment.64.29%.Conclusion:It was preliminarily determined that the solid-state fermentation medium of strain LG-9 was millet,and the nutritional components were sucrose,peptone and Ca Cl₂.The fermentation conditions were as follows:LG-9 strain were inoculum 15% and initial water content 60%,the initial p H was 7.5,the culture temperature was 28°C and the fermentation time was 9 days,the number of bacteria increased significantly;Strain LG-9 could inhibit the mycelial growth and micro sclerotia formation of Verticillium dahliae.The sterile filtrate of the fermentation broth of the strain could inhibit the germination of the micro sclerotia of Verticillium dahliae.Sterile filtrate stock solution and strain LG-9 could reduce the damage of microbacteria to cotton seedlings.Using 5%inoculants to cultivate cotton seedlings can significantly reduce the incidence rate of Verticillium dahliae,and promote the stem diameter,plant height and leaf number of cotton seedlings.The germination rate of cotton seedlings will be inhibited if the dosage of inoculant exceeds 10%.