A three-year study was conducted to evaluate the use of a nonaflatoxin-producing strain of Aspergillus parasiticus (NRRL 13539) as a biocompetitive agent for the control of preharvest aflatoxin contamination of peanuts. The agent was added to the soil of the environmental control plot facility at the National Peanut Research Laboratory and tested by subjecting peanuts to optimal conditions for the development of aflatoxin contamination. Edible peanuts from the treated soil contained aflatoxin concentrations of 11, 1, and 40 ppb for crop years 1987, 1988, and 1989, respectively, compared to untreated peanuts with 531, 96, and 241 ppb, respectively. In addition, treatment in 1989 with low and high inoculum levels of a UV-induced mutant from the NRRL 13539 strain resulted in aflatoxin concentrations of 29 and 17 ppb, respectively, in edible peanuts. Soil populations of the biocompetitive agents were not higher than populations of wild strains of A. flavus/parasiticus in untreated soil subjected to late-season drought stress. This is an important ecological consideration relative to the utilization of this biocontrol system.

Aflatoxin contamination of crops is frequent in warm regions across the globe, including large areas in sub-Saharan Africa. Crop contamination with these dangerous toxins transcends health, food security, and trade sectors. It cuts across the value chain, affecting farmers, traders, markets, and finally consumers. Diverse fungi within Aspergillus section Flavi contaminate crops with aflatoxins. Within these Aspergillus communities, several genotypes are not capable of producing aflatoxins (atoxigenic). Carefully selected atoxigenic genotypes in biological control (biocontrol) formulations efficiently reduce aflatoxin contamination of crops when applied prior to flowering in the field. This safe and environmentally friendly, effective technology was pioneered in the US, where well over a million acres of susceptible crops are treated annually. The technology has been improved for use in sub-Saharan Africa, where efforts are under way to develop biocontrol products, under the trade name Aflasafe, for 11 African nations. The number of participating nations is expected to increase. In parallel, state of the art technology has been developed for large-scale inexpensive manufacture of Aflasafe products under the conditions present in many African nations. Results to date indicate that all Aflasafe products, registered and under experimental use, reduce aflatoxin concentrations in treated crops by >80% in comparison to untreated crops in both field and storage conditions. Benefits of aflatoxin biocontrol technologies are discussed along with potential challenges, including climate change, likely to be faced during the scaling-up of Aflasafe products. Lastly, we respond to several apprehensions expressed in the literature about the use of atoxigenic genotypes in biocontrol formulations. These responses relate to the following apprehensions: sorghum as carrier, distribution costs, aflatoxin-conscious markets, efficacy during drought, post-harvest benefits, risk of allergies and/or aspergillosis, influence of Aflasafe on other mycotoxins and on soil microenvironment, dynamics of Aspergillus genotypes, and recombination between atoxigenic and toxigenic genotypes in natural conditions.

The major mycotoxin problem in Australia is the formation of aflatoxins in peanuts by Aspergillus flavus and A. parasiticus. This is controlled by good farm management practice, segregation into grades on aflatoxin content at intake to shelling facilities, colour sorting and aflatoxin assays. A second problem is the potential presence of ochratoxin A in grapes and grape products, resulting from infection by Aspergillus carbonarius. Good quality control before and during wine making ensures ochratoxin A is kept to very low levels, but in dried vine fruit, ochratoxin A levels may be higher. Biocontrol by competitive exclusion has been developed as the most promising means of controlling aflatoxins in peanuts. Some details of the process are given, including some basic laboratory experiments.

In the present study, a method for screening non-aflatoxigenic Aspergillus flavus in soil samples collected from major peanut-growing regions of China was developed. The single colonies were picked and cultured on Aspergillus flavus and parasiticus agar (AFPA). If the reverse side of the colony on AFPA was orange-coloured, it was considered A. flavus or Aspergillus parasiticus. After the genomic DNA of each strain was extracted, 28S rRNA and calmodulin were amplified and sequenced to determine the species. The key gene, aflR, was amplified and digested via polymerase chain reaction-restriction fragment length polymorphism. The aflatoxigenic A. flavus and the non-aflatoxigenic A. flavus and A. parasiticus were distinguished by enzyme digestion of aflR. 156 strains of A. flavus were screened, which consisted of 135 aflatoxigenic and 21 non-aflatoxigenic strains. The aflatoxin producing ability of each strain was confirmed using solid-state fermentation experiments. Using the method developed in the present study, we confirmed that the non-aflatoxigenic A. flavus strains isolated lost their capacity to produce aflatoxins. Considering there could be some alterations in other functional genes, some non-aflatoxigenic strains could be identified inaccurately as aflatoxigenic strains, although that did not occur in the present study. The growth of non-aflatoxigenic A. flavus was observed, and the most rapidly growing non-aflatoxigenic strain was selected for plate confrontation assays and toxic mixed culture experiments. The inhibition rate of non-aflatoxigenic A. flavus against aflatoxigenic A. flavus was 55.4 and 72.6% in potato dextrose agar (PDA) plate and natural soybean medium, respectively. The screened non-aflatoxigenic A. flavus strains provide a microbial resource for biological control of aflatoxin contamination.

Aflatoxins are potent Aspergillus mycotoxins that contaminate food and feed, thereby impacting health and trade. Biopesticides with atoxigenic Aspergillus flavus isolates as active ingredients are used to reduce aflatoxin contamination in crops. The mechanism of aflatoxin biocontrol is primarily attributed to competitive exclusion but, sometimes, aflatoxin is reduced by greater amounts than can be explained by displacement of aflatoxin-producing fungi on the crop. Objectives of this study were to (i) evaluate the ability of atoxigenic A. flavus genotypes to degrade aflatoxin B1 (AFB1) and (ii) characterize impacts of temperature, time, and nutrient availability on AFB1 degradation by atoxigenic A. flavus. Aflatoxin-contaminated maize was inoculated with atoxigenic isolates in three separate experiments that included different atoxigenic genotypes, temperature, and time as variables. Atoxigenic genotypes varied in aflatoxin degradation but all degraded AFB1 >44% after 7 days at 30°C. The optimum temperature for AFB1 degradation was 25 to 30°C, which is similar to the optimum range for AFB1 production. In a time-course experiment, atoxigenics degraded 40% of AFB1 within 3 days, and 80% of aflatoxin was degraded by day 21. Atoxigenic isolates were able to degrade and utilize AFB1 as a sole carbon source in a chemically defined medium but quantities of AFB1 degraded declined as glucose concentrations increased. Degradation may be an additional mechanism through which atoxigenic A. flavus biocontrol products reduce aflatoxin contamination pre- or postharvest. Thus, selection of optimal atoxigenic active ingredients can include assessment of both competitive ability in agricultural fields and their ability to degrade aflatoxins.

为掌握襄阳市主要花生种植区土壤中黄曲霉菌的分布和产毒特征，从襄阳市主要花生种植区采集土壤样品36份，进行黄曲霉菌分离、鉴定和产毒力研究。结果表明，襄阳市不同花生种植区土壤中黄曲霉菌落数平均为5997.6 cfu/g，且分布存在显著差异，菌落数由高到低依次为襄州、枣阳、宜城、谷城；鉴定获得黄曲霉菌株中产毒菌株占63.6%，产毒量范围 ND~304.9 μg/L，不产毒菌株占36.4%；产毒菌株可分为7种产毒类型组合，其中同时产AFB1、AFB2和AFG1三种类型的黄曲霉菌占比最多，为54.0%。在适宜培养条件下，产毒力分析结果为襄州地区每克土壤中黄曲霉菌产AFT的理论值最高，可达2080.0×103 μg/L，且其中分离出的菌株平均产毒量最高，为218.7 μg/L。可以看出襄阳市花生代表性产区土壤中黄曲霉菌分布数量显著高于我国南、北方花生主产区的平均水平，但其菌株的平均产毒能力却远低于全国其它地区。本研究初步得出了襄阳市花生主产区黄曲霉菌的分布特征和产毒特征，可为襄阳市花生黄曲霉毒素防控提供理论依据。

Aflatoxin contamination of food and feed stuff is a serious health problem and significant economic concerns. In the present study, the inhibitory effect of Candida parapsilosis IP1698 on mycelial growth and aflatoxin production in aflatoxigenic strains of Aspergillus species was investigated.Mycelial growth inhibitions of nine strains of aflatoxigenic and non-aflatoxigenic Aspergillus species in the presence of C. parapsilosis investigated by pour plate technique at different pH, temperature and time of incubation. Reduction of aflatoxin was evaluated in co-cultured fungi in yeast extract sucrose broth after seven days of incubation using HPLC method. The data were analyzed by SPSS 11.5.The presence of the C. parapsilosis at different pH did not affect significantly the growth rate of Aspergillus isolates. On the other hand, temperature and time of incubation showed to be significantly effective when compared to controls without C. parapsilosis (P≤0.05). In aflatoxigenic strains, minimum percentage of reductions in total aflatoxin and B1, B2, G1, G2 fractions were 92.98, 92.54, 77.48, 54.54 and 72.22 and maximum percentage of reductions were 99.59, not detectable, 94.42, and not detectable in both G1 and G2, respectively.C. parapsilosis might employ as a good biocontrol agent against growth and aflatoxin production by aflatoxigenic Aspergillus species.

为掌握湖北省花生种植区土壤中黄曲霉菌的分布和产毒特征，从罗田、红安、钟祥、襄阳四个典型花生种植区采集土壤样品40份，并进行黄曲霉菌分离、鉴定和产毒力研究。研究结果表明：湖北省不同花生种植区共分离鉴定到黄曲霉菌51株，土壤中黄曲霉菌落数为127.5cfu/g，不同种植区土壤中黄曲霉菌分布存在显著差异，钟祥土壤中黄曲霉菌落数最高，罗田最低；鉴定获得黄曲霉菌株中产毒菌株占96%，产毒量范围0～227.81μg/L，不产毒菌株占4%；产毒菌株分为只AFB1、只产AFB1和AFB2、只产AFB1、AFB2、AFG1和产AFB1、AFB2、AFG1、AFG2毒素4种类型，其中以只产AFB1和AFB2的菌株占比最高，为65%；不同种植区黄曲霉菌株产毒力研究发现，钟祥每克土壤中黄曲霉菌产AFB1的量最高，达11679.70μg/L。本研究可为湖北花生黄曲霉毒素污染预警和防控提供理论依据。