Studies On Isolation And Identification Of Aspergillus Flavus And Its Aflatoxin In Buckwheat And Optimum Growth Conditions

Buckwheat,as an important crop of miscellaneous grain,has unique nutritional value and rich active substances,which is more and more favored by people all over the world,and the demand is gradually increasing.Aspergillus flavus and aflatoxin seriously endanger people’s health,have strong toxicity and carcinogenicity,and being contaminated by aflatoxin can cause great economic losses.There are few reports of aflatoxin contamination in buckwheat,In this study,33 buckwheat varieties were used as materials to study the average carrier rate in different tissues such as roots,stems,leaves,seeds and soils of different varieties of buckwheat,isolation and identification of Aspergillus flavus strains and to detect and analyze the production of aflatoxin in grain and culture,the optimum growth and toxicity conditions of Aspergillus flavus strains in buckwheat were studied in order to provide basis for safe production and health protection of buckwheat industry.The main results were as follows:1.234 strains were isolated from different buckwheat tissues（roots,stems,leaves,seeds）and soil attached to the roots,all of them were Aspergillus flavus by morphological and molecular identification.2.There were total of 7 types of toxicity production and showed that Aspergillus flavus native to buckwheat were mainly produced AFB₁ and AFG₂.The results of aflatoxin type indicate that the production of G toxins is bound to produce B toxins.The results showed that the lowest production toxins types of strains were the dominant strain in buckwheat,compared with peanut,corn and other crops,the toxin production ability of Aspergillus flavus strain in buckwheat is not high.3.Aspergillus flavus is widely found in different tissues of different buckwheat varieties,but there were significant differences among different types of buckwheat,among different varieties and among different tissues（P<0.05）,and the rice tartary buckwheat has the largest variant carrier rate range of 0-63.96%in seeds;the variation of soil carrier rate in conventional tartary buckwheat,common buckwheat and F.tatari-cymosum were the largest,with 0-100%,0-60%,20-40%,respectively;Detection rate order is AFB₁>AFG₁>AFB₂>AFG₂ of four aflatoxins from different grains,the main contents of grain AFB₁,followed by AFG₁、AFB₂ and AFG₂.only one tested variety exceeded the standard,the overall excess rate was 3.03%.4.Correlation analysis of different types of buckwheat tissues with carrier rate,agronomic characters and AFT in seeds showed that there was different correlation between different factors of buckwheat and seed carrier rate.Among them,the ratio of seed length to width was positively correlated with the rate of seed carrier rate in rice tartary buckwheat,there was a significant positive correlation between plant height and number of grains per plant and seed carrier rate in conventional tartary buckwheat,a significant positive correlation between the number of nodes and seed carrier rate in common buckwheat.There are no correlation in tartary buckwheat,and all variables had no significant effect on total seed toxicity（AFT）.5.Validation test on the cultivation of varieties with lower carrier rate,found that the leaves and seeds of most buckwheat varieties with low carrier rate were not or basically not infected and produce toxic,indicating their certain resistance to Aspergillus flavus.6.The strain MI18-S1 of buckwheat can produce toxin B₁ and B₂,among them,B₁ is dominant;when the temperature is 28℃and the water activity a_w is 0.93,the strain produces the most spores and toxin.When the temperature was lower than 15℃or higher than 42℃,there are few growth of the strain and few production of toxin.With temperature increase in the range of 15-42℃,the toxin production increased at first and then decreased;The results of multivariate linear regression analysis showed that the linear effect of colony diameter on aflatoxin production was not significant,and the amount of aflatoxin production was mainly affected by three factors:water activity,temperature and sporulation.The amount of sporulation was the most important;It was found that the amount of sporulation was mainly influenced by four factors:water activity,temperature,aflatoxin production and colony diameter,and the amount of aflatoxin production was the most important.