| Southern blight of peanut is a soil-borne fungal disease caused by Sclerotium rolfsii Sacc.In recent years,due to the continuous expansion of peanut planting area,continuous cropping and straw returning to the field and other farming methods are becoming more and more common,coupled with climate warming,the improvement of water and fertilizer conditions and the reduction of organic fertilizer application,Southern blight of peanut is common in the main peanut producing areas in China.At present,Southern blight of peanut has become an important threat to peanut production in Henan Province.In this study,12 of peanut fields infected by Southern blight were randomly selected from Zhengzhou,Kaifeng,and Xinxiang in Henan Province.The rhizosphere soil samples of both healthy and infected peanut plants were collected by a five-point sampling method.The effect of Southern blight of peanut on rhizosphere microorganisms was studied by high-throughput sequencing method;bacteria were isolated from rhizosphere soil by dilution coating method;the antagonistic strains against Southern blight of peanut were screened and identified by plate confrontation method;the effects of fermentation filtrate and high-temperature sterilization filtrate on mycelial growth were studied by shaking culture;oxford cup method was used to observe the effect of antagonistic bacterial fermentation broth on mycelial morphology;the effect of antagonistic bacteria on sclerotia germination was studied by bacteria-containing PDA plate;The pot control effect of antagonistic bacterial fermentation broth was measured in the greenhouse.The main results are as follows:1.The effects of southern blight on peanut rhizosphere microorganisms were studied by high-throughput sequencing.The results of alpha diversity showed that the abundance of rhizosphere bacteria in diseased peanuts was higher than that in healthy peanuts.The results of beta diversity showed that there were differences in community composition between the two treatments.The analysis of bacterial community structure showed that there were differences in rhizosphere bacterial communities between healthy peanuts and diseased peanuts.The abundance of Proteobacteria and Bacteroidota in rhizosphere soil of infected plants increased by 2.97% and 3.19%,respectively;At the genus level,in the rhizosphere soil flora of healthy plants,norank_f__norank_o__Vicinamibacterales increased by 1.71%,norank_f__Vicinamibacteraceae increased by 1.12%,Pseudomonas by 1.09% and Bacillus by 1.63%.The results of Functional Annotation of Prokaryotic Taxa analysis showed that the functions of bacteria in rhizosphere soil were mainly concentrated in chemoheterotrophy and aerobic chemoheterotrophy.The occurrence of southern blight of peanut improved the functions of dark oxidation of sulfur compounds,cyanobacteria,and oxygenic photoautotrophy abundance of bacteria in peanut rhizosphere soil.2.A total of 570 strains of bacteria were isolated from rhizosphere soil.Through the plate confrontation training with southern blight on peanut,four dominant bacteria HNZZ-23,HNKF-5,HNXX-14 and HNXX-169 were selected according to the length of antibacterial activity time and repeatability.The inhibition rates of mycelial growth were 77.04%,78.48%,72.79%,and 71.10% respectively.Through physiological,biochemical,and molecular biological identification,HNZZ-23 was identified as Bacillus atrophaeus,HNKF-5 as Bacillus pumilus,HNXX-14 as Pseudomonas aeruginosa,and HNXX-169 as Bacillus subtilis.3.The effects of antagonistic bacterial fermentation broth on the growth rate,mycelial morphology,and sclerotinia germination of southern blight on peanut fungus were determined.The effect of antagonistic bacteria fermentation broth on mycelial growth rate was measured by the shaking culture method.The results showed that the fermentation filtrate and high-temperature sterilization filtrate of four antagonistic bacteria could significantly inhibit mycelial growth.The mycelial growth rate of the treatment group was slow,and the inhibition rate of mycelial growth was generally more than 70%.HNZZ-23 filtrate had little effect on the inhibition of mycelial growth after high-temperature sterilization,and the other three antagonists had a slight effect on mycelial growth after high-temperature sterilization,but the overall inhibition rate was more than 70%.The Oxford cup method was used to observe the effect of antagonistic bacterial fermentation broth on mycelial morphology.In the control group the results showed that,the hyphae were slender,uniform in thickness,and vigorous in growth;the hyphae of the four treatment groups were abnormal,the hyphae became shorter,the branches increased,and the branches were slender,and the hyphal density became smaller.The effect of Antagonistic Bacteria on sclerotia germination was studied by using the bacteria-containing PDA plate.The results showed that the four antagonistic bacteria could significantly inhibit Sclerotinia germination,and the higher the bacterial concentration,the stronger the inhibition rate of Sclerotinia germination.4.The pot control effect of antagonistic bacterial fermentation broth was measured in the greenhouse.The results showed that HNZZ-23 and HNXX-14 had certain control effects on Southern blight of peanut under greenhouse conditions,which were 30.50% and 25.73%respectively,and HNKF-5 and HNXX-169 had poor control effects on peanut,which were3.84% and 4.79% respectively.5.The growth-promoting effect of fermentation broth of four antagonistic bacteria on peanuts was measured in the greenhouse.By measuring the length,fresh weight,and dry weight of the aboveground and underground parts of peanut plants,the results showed that the length and weight of aboveground and underground parts of HNZZ-23 fermentation broth irrigation treatment were significantly higher than CK,which had a significant promoting effect on the growth of peanut plants.The synergistic effects on root length,stem length,root fresh weight,stem fresh weight,root dry weight,and stem dry weight were 20.46%,14.47%,13.20%,19.28%,9.78%,and 18.39% respectively.Root irrigation with HNKF-5,HNXX-14,and HNXX-169 fermentation broth did not affect the growth of peanut plants.The above results showed that the fungus of southern blight of peanut increased the abundance and diversity of peanut rhizosphere bacteria,and increased the abundance of dark oxidation of sulfur compounds,cyanobacteria,and oxygenic photoautotrophy.The four antagonistic bacteria isolated and screened from peanut rhizosphere soil had strong inhibitory effects on mycelial growth and sclerotia germination in vitro.Combined with the results of the pot experiment,HNZZ-23 was a biocontrol strain with the control effect on southern blight of peanut and promoted the growth of peanut plants.By analyzing the differences in microbial community diversity and function in the rhizosphere of peanut plants caused by southern blight of peanut,and measuring the in vitro activity and pot control effect of four antagonistic bacteria,we can find new biocontrol strains and provide new control ideas for the biological control of outhern blight of peanut. |
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