Study On The Effects Of Peanut Geocarposphere Micro-ecological Environment On Aflatoxin Contamination

Peanut(Arachis hypogaea)with large quantities of unsaturated fatty acids,protein,mineral elements and antioxidants is one of the major oil crops and economic crops and few export advantage agro-product in China.However,peanut is susceptible to be infected by Aspergillus flavus and then aflatoxin(AFT)accumulation through all links from productions to sales,which seriously threatens the peanut consumption safety and limits industrial development.Preharvest infection and postharvest infection both contribute to peanut AFT contamination.The preharvest contamination in the fields was the major reason of AFT contamination as well as the source of storageperiod contamination.Peanut AFT contamination in the field is the result of the interaction among Aspergillus flavus,soil microenvironment and peanut.In this study,based on the preliminary work on distribution of the peanut aflatoxin contamination conducted by our lab,3 provinces(Jiangxi,Shandong and Liaoning)were selected as the test areas which represented different degrees of aflatoxin contamination.Cooperated with pot experiment,with high-throught microbial diversity sequencing technology,the effect of micro-ecological environment of peanut geocarposphere soilon aflatoxin contamination,including soil physicochemical property and microbial communities structure was investigated,thus to provide a solid technical support for early warning and precisely prevention and controlling peanut aflatoxin contamination in the field,The main research contents are as follows:1.The main soil microbial environmental factors affecting the peanut aflatoxin contamination in the field were focused primarily: soil exchangeable calcium and geocarposphere microbial flora structure.Based on the analysis of cadmium in soil and peanut and aflatoxin in peanut in main producing areas for 5 years,combined with analysis of more than 12 factors including cadmium,organic matter,total nitrogen,available phosphorus,exchangeable calcium,copper and microbial flora structure of peanut soil from the three designated sites-Zhangshu(Jiangxi),Linyi(Shandong)and Fuxin(Liaoning),the results showed that there were correlations between the content of calcium and the structure of microbial flora with the level of aflatoxin contamination in peanut in different producing areas of China.The soil exchangeable calcium content and microbial flora structure were preliminarily identified as the main micro-ecological environment factors,which caused the different level of aflatoxin contamination in peanut among the three ecological zones.2.Relationship between the exchangeable calcium content in soil and the accumulation of calcium content in peanut shell,seed coat and seed along with the resistance ability of peanut to Aspergillus flavus was preliminarily proved.Experimental results of two years field test based on the three above-mentioned designed sites and potted test based on adding different gradient content exchange calcium into the soil showed that the exchangeable calcium in soil had a positive correlation(r?0.98)with shell thickness,calcium in shell,calcium in seed coat and calcium in seed.The higher the soil exchangeable calcium content,the more calcium nutrition in different parts of peanut enriched;calcium in seed and seed coat had a strong negative correlation(r<-0.95)with Aspergillus flavus infection index.The higher calcium content in peanut seed and coat,the lower the Aspergillus flavus infection index and the higher resistance to infection of seeds gained.It provides technical ideas for the precision prevention and control of aflatoxin contamination in the high risk area in China.3.Analyzed the relationship between the microflora of peanut geocarposphere and the aflatoxin contaminationThe structure of microbial community in peanut soil in typical ecological regions was analyzied by high throughput sequencing technology combined with multivariate statistical analysis.The result showed that there were significant differences in the structure of the microbial community from the geocarposphere soil of three typical peanut samples,There was an order of alpha diversity of bacterial community among peanut soil: Zhangshu(Jiangxi)>Linyi(Shandong)>Fuxin(Liaoning),while the alpha diversity of fungal present opposite situation.To figure out the relationship of peanut soil microbial community structure and aflatoxin contamination,Aspergillus flavus was artificial inoculated to peanut soil before a month harvest,the changes of microbial community structure were studied.The results of PCA and PCoA showed that under the inoculation,there were significant differences of microbial flora composition and abundance and community structure in peanut soil compared with blank control.In detail,the ? diversity of bacteria increased and abundance distribution more uniformed,the potential biocontrol bacterial of Bacillus,Lactococcus and Ralstonia have more stronger interaction with others bacteria;the decreased ? diversity of fungi and increased dominant concentration index.In conclusion,the ? diversity of microbial populations is related to the risk of Aspergillus flavus infection,therefore the ? diversity of soil bacteria and fungi can be used as an early warning index of the risk of Aspergillus flavus infection,providing a technical support for the establishment of the large scale warning model for peanut aflatoxin in China.