Study On Rhizosphere Microbes In Peanut Root Rot Under Continuous Cropping And Rotation

Peanut is an important oil and cash crop in China.Therefore,the stable and high yield of peanut is of great significance to the development of agriculture in China.However,due to the gradual decrease of the arable land area,China’s peanut planting areas often present the re-seeding pattern,resulting in the frequent occurrence of peanut rootrot,which greatly restricts the sustainable development of the peanut industry.Previous studies have found that the high incidence of peanut root rot in continuous cropping is closely related to the imbalance of rhizosphere microorganisms.In this paper,the mechanism of high incidence of peanut root rot in continuous cropping was explored from the aspects of disease inhibition ability,composition of rhizosphere microbial community,and functions of typical microorganisms in rhizosphere.The main research results are as follows:1)The field investigation experiment found that the peanut underground and aboveground growth indicators were significantly lower than the rotation crop peanuts during the whole growth period,and the pod formation period was the most obvious;the incidence of continuous peanut root rot increased significantly,and the incidence of peanut root rot reached 100%at the pod formation period.Fluorescence quantitative PCR analysis found that the number of Fusarium oxysporum in the continuous cropping peanut was significantly higher than that of the rotated peanut(p<0.05),and reached the highest value at the harvesting period of 1.42×10~3copies/g dry soil.The effects of continuous cropping on peanut growth and root rot were further tested by potted experiment.The reasons for the high incidence of continuous peanut root rot were analyzed from the perspective of rhizosphere microbial resistance.The direct confrontation experiments showed that the inhibition rate of the rhizosphere bacteria in continuous cropping peanuts was significantly lower than that the rhizosphere bacteria of rotation peanuts by16.2%～46.0%.The indirect confrontation experiments showed that the inhibition rate of the rhizosphere bacteria in continuous cropping peanuts was significantly lower than that the rhizosphere bacteria of rotation peanuts by 46.7%～58.5%.In addition,the biomass of F.oxysporum showed a significant upward trend in rhizosphere bacteria of continuous cropping peanut(p<0.05).The bacteria volatiles were collected by solid phase microextraction and were determined by gas chromatography mass spectrometry.Total of12 volatile organic compounds were detected in bacteria volatiles,which were mainly classified into sulfides,olefins,alcohols,ketones and aldehydes.Compared with the rhizosphere bacterial volatiles of rotating peanut,the relative content of the dimethyl sulfide,dimethyl disulfide,1,3-xylene,styrene,6-methyl-3,5-Pentadien-2-one,Spiro[4.5]dec-7-ene,1,8-dimethyl-4-(1-methylethenyl)-,(1S,4R,5S)-(-)-andα-calicitol were reduced in the bacteria volatiles of continuous cropping peanut.2)Through the 16S r RNA high-throughput sequencing method,the effects of continuous cropping conditions on the rhizosphere microbial composition of peanut during seedling stage were investigated.The results showed that the Shannon index and Simpson index of the rhizosphere microorganisms in the continuous cropping peanuts were significantly lower than those in the rhizosphere microorganisms of rotating peanuts.Under the level of phylum classification,the relative abundance of Alphaproteobacteria,Betaproteobacteria,Acidobacteria and Bacteroidetes were significantly increased in rhizosphere microbe of continuous cropping peanut compare with rotating peanuts,but the relative abundance of Gammaproteobacteria and Actinobacteria was significantly reduced(p<0.05).Under the level of family classification,the relative abundance of Burkholderiaceae and Caulobacteraceae was significantly increased by 53.0%and 41.9%in rhizosphere microbe of continuous cropping peanut compare with rotating peanuts,but the relative abundance of Sphingomonadaceae,Pseudomonadaceae,Paenibacillaceae and Micrococcaceae was significantly reduced by 55.9%,43.5%,26.8%,and 69.5%in(p<0.05).The relative abundance of Ralstonia sp.in the Burkholderiaceae was significantly increased by 125%in rhizosphere microbe of continuous cropping peanut compare with rotating peanuts,but the relative abundance of Pseudomonas sp.and Paenibacillus sp.in the Pseudomonadaceae and Paenibacillaceae were significantly reduced by 67.6%and 57.8%(p<0.05).3)Finally,the rhizosphere microbial composition of peanut under continuous crop and rotation was analyzed by classical cultureable separation(plate smearing method and plate streaking method and the 16S r RNA high-throughput sequencing method.The results showed that the main bacteria of continuous cropping of peanut was Stenotrophomonas sp.and Burkholderia sp..The main bacteria of rhizosphere separation of rotating peanut was Pantoea sp.、Paenibacillus sp.、Sporosarcina sp.、Pseudomonas sp.、Lysinibacillus sp.、Fictibacillus sp.and Enterobacter sp..Further,from the growth promotion,the production of membrane capacity and the response of peanut root exudates,it was found that the typical strains of continuous cropping of peanut roots had lower IAA and inhibition ability,but the ability to produce membranes was stronger and the response to peanut root exudates was obvious.The physiological differences of bacteria may be important reasonc aused by the continuous existence of continuous cropping peanuts.