Screening Of High Efficient Biocontrol Agents And Fungicides For Cotton Damping-off With In Vivo Assay

Cotton damping-off disease, which mainly caused by Rhizoctonia solani, is one of the important soil-bore diseases in cotton. Until now, no effective and environmental friendly measures could be achieved in suppressing against cotton damping-off disease. Microbial fungicides have been confirmed as an effective measure to suppress crop soil-borne diseases, and screening the biocontrol agents is the prerequisite for developing microbial fungicides. The mechanisms of biocontrol of soil-borne diseases by biocontrol agents include their ability to inhibit the growth of phytopathogens by producing antifungal active compounds, their competition for nutrients and space with pathogens, and their ability to induce resistance in plant. Considering all these factors, and building a rapid and effective method to screen biocontrol agent, that is important for developing microbial fungicides. In this study, a method for screening biocontrol agents against cotton damping-off was built up, with this method, six potential biocontrol strains and 6 chemical fungicides were selected for effective control of cotton damping-off.1. Building up a bioassay method for rapid screening control agents against cotton damping-off. Cotton damping-off was selected as biocontrol objective, the inoculation object and quanlity and depth of R. solani were optimized. The result indicated that using the millet shell as a vector for inoculating R. solani, and the depth of the millet with R. solani is 4.5 cm to cotton seed could obtain a suitable occurrence of the disease for biocontrol evaluation.2. With the evaluation method, six potential biocontrol strains were selected from a total of 2000 strains of antagonistic bacteria. The biocontrol efficiency of strains HMB27756, HMB27723, HMB27703, HMB28179, HMB27676 and HMB28593 respectively were 63.58%, 55.32%, 53.10%, 44.73%, 35.61% and 33.55%, respecively.3. Biocontrol strains HMB27756, HMB27723, HMB27703, HMB28179, HMB27676 and HMB28593 were identified with gyr B and 16 S r DNA sequence,as well as the Biolog phenotype Microarray technology, respecitively. Results confirmed that strain HMB27756 and HMB28179 were B. amyloliquefaciens, strain HMB27723, HMB27703, HMB27676 and HMB28593 were B. subtilis.4. The plant growth-promoting activity of selected strains were evaluated in this study. Results indicted that all of the tested strains had a significant growth-promoting activity. Among which, strain HMB27756 could significantly promote cotton root-length, stem length, plant fresh weight above the ground and the plant fresth weight under the ground.5. The antifungal activity of strain HMB27756, HMB27723, HMB27703, HMB28179, HMB27676 and HMB28593 were tested against the growth of different pathogens. Results revealed that the 6 biocontrol strains showed a strong antifungal activity against the growth of Rhizoctonia solani, Botrytis cinerea, Verticillium dahliae, and Fusarium oxysporum f. sp. vasinfectum.6. Fourteen chemical fungicides were evaluated for effective suppression for cotton damping-off disease with the bioassay method in this study as well. Six chemical fungicides were selected, and control efficacies were 56.87%, 55.92%, 52.31%, 47.64%, 36.54% and 34.80%, respectively.