Screening Of Non-toxigenic Aspergillus Flavus Strains And Application In Peanut Planting

Aflatoxin(AFT)is a kind of secondary metabolite produced by Aspergillus flavus(A.flavus)and Aspergillus parasiticus(A.parasiticus),which cause extensive pollution to peanut,maize and other food crops,oils and their products.It seriously threatens human health because of its carcinogenic,teratogenic and mutagenic effects.Because of genetic variation,some A.flavus strains lost their ability to produce aflatoxin.Non-toxigenic A.flavus strains can competitively inhibit the growth of aflatoxin-producing Aspergillus strains in the process of cultivation and storage,so as to control aflatoxin pollution from the source.In this study,screening of non-toxigenic A.flavus strains,preparation of biocontrol agents and evaluation of field application effects were carried out in several major peanut producing areas in China,as well as areas with serious aflatoxin contamination,such as Wuyang in Henan Province and Xiangyang in Hubei Province.Firstly,156 strains of A.flavus were isolated and identified from soil and peanut samples in Hebei,Henan and Hubei Province by using morphological,analytical chemistry and molecular biology techniques such as PCR-RFLP method.Among them,21 strains(13.5%)were non-toxigenic A.flavus and 135 strains(86.5%)were toxigenic A.flavus.Next,non-toxigenic A.flavus was used to prepare different biocontrol agents,such as microbial fertilizer based on peanut meal and soybean,rice inoculated with spore agent,liquid spores biocontrol agent and peanut coating agent.Different application time and dosage were set to evaluate the application effect of different biocontrol agents through field experiments.The results of field experiment showed that the dosage had no effect on the results of field experiment,and the optimum time for applying fungicides was 2~3 weeks at the beginning of flowering.The study on the colonization of non-toxigenic A.flavus in soil showed that the density of non-toxigenic A.flavus in soil increased significantly and the proportion of non-toxigenic A.flavus increased significantly after the application of non-toxigenic A.flavus agent.According to the effect of colonization,the validity of inoculant application was as follows: rice inoculant with spores > coating > peanut meal / soybean microbial fertilizer > liquid spore agent.The detection results of aflatoxin content in peanut showed that there was almost no aflatoxin in the treated groups and the control groups at the early harvest stage.After three months of warming and humidifying storage,the content of aflatoxin in the groups treated with non-toxigenic A.flavus agent decreased by 10.39% to 87.74% compared with that in the control group without inoculated with non-toxigenic A.flavus agent.The results showed that there were significant differences among the fungicides: rice inoculant with seed > peanut meal / soybean microbial fertilizer > coating agent > liquid spore agent.In this study,a rapid,efficient and accurate screening method for non-toxigenic A.flavus strains was established,and 21 non-toxigenic A.flavus strains were obtained by this method.Different biocontrol agents were prepared by non-toxigenic A.flavus strains,and their application effects were evaluated according to field test results.It provided data support for screening non-toxigenic A.flavus strains,preparation of biocontrol agents and field test evaluation technology,and it provided strong technical support for product development and industrial application of biological control strains of aflatoxin.