Study On The Distribution,potential Of Aflatoxigenic Fungi And Toxins Contamination In Peanut Soils

Peanut is important oil crop and economic crop in China.However,it is susceptible to aflatoxin contamination,which threatens human health and causes great economic losses.Aflatoxin is a secondary metabolite produced by aflatoxigenic fungi such as Aspergillus flavus and A.parasitcus.They are highly toxic and carcinogenic.Peanut flowers aboveground and pods grow underground,and A.flavus colonized in peanuts has direct correlationship with it in soil.Through isolation,identification and the difference in aflatoxin producing potential of A.flavus and A.parasitcus,the distribution and aflatoxin-producing pattern of A.flavus and A.parasitcus in the soil of main peanut producing area in China will be known,and then the relationship among fungi distribution,aflatoxin-producing potential,climatic conditions and aflatoxin contamination will be discussed.It will provide theoretical basis and statistical support for prevention and precisely control of aflatoxin contamination in peanuts,ensure peanut consumption safety and promote the improvement of peanut industry.1.A.flavus and A.parasiticus resources in soil of peanut main producing area in China wereestablishedA total of 58 representative counties or cities were selected from 15 major peanut producingprovinces belong to four peanut production ecological areas?northeastern area,northern area,Yangtze River basin area and southern area?in China and about 580 rhizosphere soil samples were collected.Then 477 strains of Aspergillus genus were isolated,purified and identified by morphology and molecular biology method.Herein,470 strains were Aspergillus flavus with the proportion of 98%and 7 strains were A.parasitcus.By further integration and analysis,a Aspergillus genus resource which assembles origin,environment of sampling sites,colony morphological characteristics,ITS information,chemotypes and aflatoxin production potential of strains isolated from peanut soil in main producing area in China were constructed.2.A.flavus distribution in peanut soil of main producing provinces in China were determinedResults showed that there were significantly regional variation in the populations and frequency of A.flavus in the soil of four peanut production ecological areas in China.Yangtze River Basin area had the most populations?135.71cfu/g?and highest frequency?57.62%?of A.flavus,followed by southern area and northern area.Northeastern area had the least populations and lowest frequency of A.flavus,with A.flavus populations of 157.14cfu/g and frequency of 12.86%.The correlation between the CFU of A.flavus and climatic conditions in different producing areas was analyzed.Result showed that there was a positive relationship between the average CFU and climatic conditions a month before harvest.In Fengcheng?Jiangxi Province?and Chuzhou?Anhui Province?of Yangtze River Basin area,A.flavus populations were 410 and 380cfu/g,respectively,with the average temperature up to 28.56?a month before harvest.It significantly higher than Qiqigaer?Heilongjiang??10cfu/g?and Zhangwu?Liaoning??20cfu/g?,where average temperature was 17.72?a month before harvest.3.Aflatoxin producing pattern of A.flavus in peanut soil of main producing provinces in China weregraspedAflatoxin producing potential was analyzed in the identified A.flavus by HPLC.It showedthat 377 of them were aflatoxigenic strains with the proportion of 79%.The remaining 100 strians were atoxigenic strains.Dominant chemotype of A.flavus producing only AFB₁ and AFB₂ with the proportion of 75%.The proportion of strains producing both B group and G group aflatoxins was 4%,which mainly resided in Changtu?Liaoning?and Pingdu?Shandong?.It indicated that there were significantly regional variation in the aflatoxin producing potential.The aflatoxin producing potential range of A.flavus from southern area was 0-106.74?g/L,with average AFB₁ content of 53.98?g/L.Aflatoxin producing potential of A.flavus from Yangtze River Basin area,with the AFB₁ range of0-128.3?g/L and average AFB₁ content of 46.13?g/L.A.flavus isolated from northeastern area and nothern area had lower aflatoxin producing potential.4.Peanut aflatoxin contamination was related with A.flavus population and aflatoxin producingpotential in soilThere was a positive correlation between aflatoxin producing potential per gram soil with A.flavus CFU and average aflatoxigenic potential.Average AFB₁ and AFT producing potential per gram soil among the four ecological areas showed that southern area had the maximum aflatoxin producing potential per gram soil,with the content of AFB₁ of 79010.41?g/L.Yangtze River Basin area was in the second place.Northeastern area had the minimum aflatoxin producing potential per gram soil,with the content of AFB₁ of 7993.43?g/L.The potential risk of soil contamination in the southern area is 1.39 times that of the Yangtze River Basin,5.2 times that of the north and 9.88 times of that of the Northeast China.It revealed that potential aflatoxin contamination was highest in southern area.Aflatoxin contamination analysis showed that positive aflatoxin samples and standard exceeding samples were most in southern area.Yangtze River Basin area and northern area ranked the second and third place and they were least in northeastern area.There was a significant relationship among aflatoxin contamination,isolate distribution and aflatoxigenic potential.