Screening,Identification And Evaluation Of Biocontrol Bacteria Against Root Rot Of Cotton Seedling In Xinjiang

The main root rot diseases of cotton in Xinjiang were Rhizoctonia solani Kühn and Fusarium verticillioides(Sacc.)Nirenberg.The plate confrontation method was used to measure the bacteriostatic capacity of the strains isolated in the field and many strains of biocontrol bacteria preserved in the laboratory for many years,and the cultivation conditions and the control effect in the field were studied to select the biocontrol bacteria which can effectively control the root rot disease in the seedling stage of cotton,so as to provide technical guarantee for the green development of cotton industry in Xinjiang:1.Screening of biocontrol bacteria against root rot disease in cotton seedling stageDetermination of strains A178,L18-1,TWT34,UB17-1,HWT34 and LD19-1 by Rhizoctonia solani were 80.56%,80.00%,73.05%,80.83%and 72.22%respectively.Among them,strains A178,L18-1 and UB17-1 had strong inhibition ability,with the inhibition rates above 80.00%;strains twt34 and hwt34 had inhibition rates above 70.00%;strains A178,L18-1,TWt34,UB17-1 and HWt34 had significantly higher inhibition ability than other biocontrol bacteria.Strains A178,L18-1,TWt34,UB17-1 and HWt34 all had more than 70%inhibition on Fusarium verticilliodes,Fusarium oxysporum and Verticillium dahliae.The results showed that the strains A178,L18-1,TWt34,UB17-1 and HWt34 had strong antibacterial ability to the root rot pathogens of cotton seedling.2.Taxonomic identification of five biocontrol bacteriaThe 16S rDNA gene sequence and gyrA gene sequence of biological control bacteria A178,L18-1,TWt34,UB17-1 and HWt34 were sequenced and identified respectively.Strains UB17-1,L18-1 and A178 were identified as Bacillus velezensis,biological control bacteria HWt34 and TWt34 as Bacillus mojavensis.3.Control effect of biocontrol bacteria on root rot disease of cotton at Seedling StagePot experiments showed that the control effects of UB17-1 10-2 and TWt34 10-2 on root rot of cotton seedling were 90.80%,90.18%and 90.80%respectively The control effect of 10-2 fermentation liquid soaking treatment is better,which is equivalent to that of the coating treatment of 20%mequat thiram,and the control effect is 86.17%,85.64%and 86.70%respectively.4.Optimization of culture conditions for biocontrol bacteriaThe nutritional and fermentation conditions of the liquid culture medium of Bacillus velezensis were studied and optimized by orthogonal test design,with the bacteriostatic rate of Rhizoctonia solani and Fusarium verticilliodes as the index.The optimal combination of nutritional conditions was determined as sucrose 1%,yeast extract 0.5%and dipotassium phosphate 0.2%.The fermentation conditions were as follows:pH 6.5,rotating speed 135 r/min,inoculum amount 1%,liquid loading 150 ml,fermentation temperature 32℃,fermentation time 72 h,the best bacteriostatic effect on Rhizoctonia solani;pH 6.5,rotating speed 120 r/min,inoculum amount 3%,liquid loading 200 ml,fermentation temperature 32℃,fermentation time 72 h,the best bacteriostatic effect on Fusarium verticilliodes.