Aflatoxin-producing potential of communities of Aspergillus section Flavi from cotton producing areas in the United States

Creating large chromosomal segment deletions in Aspergillus flavus by a dual CRISPR/Cas9 system: Deletion of gene clusters for production of aflatoxin, cyclopiazonic acid, and ustiloxin B

Aspergillus flavus produces hepatocarcinogenic aflatoxin that adversely impacts human and animal health and international trade. A promising means to manage preharvest aflatoxin contamination of crops is biological control, which employs non-aflatoxigenic A. flavus isolates possessing defective aflatoxin gene clusters to outcompete field toxigenic populations. However, these isolates often produce other toxic metabolites. The CRISPR/Cas9 technology has greatly advanced genome editing and gene functional studies. Its use in deleting large chromosomal segments of filamentous fungi is rarely reported. A system of dual CRISPR/Cas9 combined with a 60-nucleotide donor DNA that allowed removal of A. flavus gene clusters involved in production of harmful specialized metabolites was established. It efficiently deleted a 102-kb segment containing both aflatoxin and cyclopiazonic acid gene clusters from toxigenic A. flavus morphotypes, L-type and S-type. It further deleted the 27-kb ustiloxin B gene cluster of a resulting L-type mutant. Overall efficiencies of deletion ranged from 66.6 % to 85.6 % and efficiencies of deletions repaired by a single copy of donor DNA ranged from 50.5 % to 72.7 %. To determine the capacity of this technique, a pigment-screening setup based on absence of aspergillic acid gene cluster was devised. Chromosomal segments of 201 kb and 301 kb were deleted with efficiencies of 57.7 % to 69.2 %, respectively. This system used natural A. flavus isolates as recipients, eliminated a forced-recycling step to produce recipients for next round deletion, and generated maker-free deletants with sequences predefined by donor DNA. The research provides a method for creating genuine atoxigenic biocontrol strains friendly for field trial release.

Research Progress Related to Aflatoxin Contamination and Prevention and Control of Soils

Aflatoxins are potent carcinogenic compounds, mainly produced by fungi species of the genus Aspergillus in the soil. Because of their stability, they are difficult to remove completely, even under extreme conditions. Aflatoxin contamination is one of the main causes of safety in peanuts, maize, wheat and other agricultural products. Aflatoxin contamination originates from the soil. Through the investigation of soil properties and soil microbial distribution, the sources of aflatoxin are identified, aflatoxin contamination is classified and analysed, and post-harvest crop detoxification and corresponding contamination prevention measures are identified. This includes the team's recent development of the biofungicide ARC-BBBE (Aflatoxin Rhizobia Couple-B. amyloliquefaciens, B. laterosporu, B. mucilaginosus, E. ludwiggi) for field application and nanomaterials for post-production detoxification of cereals and oilseed crops, providing an effective and feasible approach for the prevention and control of aflatoxin contamination. Finally, it is hoped that effective preventive and control measures can be applied to a large number of cereal and oilseed crops.

Multiple Year Influences of the Aflatoxin Biocontrol Product AF-X1 on the A. flavus Communities Associated with Maize Production in Italy

AF-X1 is a commercial aflatoxin biocontrol product containing the non-aflatoxigenic (AF-) strain of Aspergillus flavus MUCL54911 (VCG IT006), endemic to Italy, as an active ingredient. The present study aimed to evaluate the long-term persistence of VCG IT006 in the treated fields, and the multi-year influence of the biocontrol application on the A. flavus population. Soil samples were collected in 2020 and 2021 from 28 fields located in four provinces in north Italy. A vegetative compatibility analysis was conducted to monitor the occurrence of VCG IT006 on the total of the 399 isolates of A. flavus that were collected. IT006 was present in all the fields, mainly in the fields treated for 1 yr or 2 consecutive yrs (58% and 63%, respectively). The densities of the toxigenic isolates, detected using the aflR gene, were 45% vs. 22% in the untreated and treated fields, respectively. After displacement via the AF- deployment, a variability from 7% to 32% was noticed in the toxigenic isolates. The current findings support the long-term durability of the biocontrol application benefits without deleterious effects on each fungal population. Nevertheless, based on the current results, as well as on previous studies, the yearly applications of AF-X1 to Italian commercial maize fields should continue.

Impact of frequency of application on the long-term efficacy of the biocontrol product Aflasafe in reducing aflatoxin contamination in maize

Aflatoxins, produced by several Aspergillus section Flavi species in various crops, are a significant public health risk and a barrier to trade and development. In sub-Saharan Africa, maize and groundnut are particularly vulnerable to aflatoxin contamination. Aflasafe, a registered aflatoxin biocontrol product, utilizes atoxigenic A. flavus genotypes native to Nigeria to displace aflatoxin producers and mitigate aflatoxin contamination. Aflasafe was evaluated in farmers' fields for 3 years, under various regimens, to quantify carry-over of the biocontrol active ingredient genotypes. Nine maize fields were each treated either continuously for 3 years, the first two successive years, in year 1 and year 3, or once during the first year. For each treated field, a nearby untreated field was monitored. Aflatoxins were quantified in grain at harvest and after simulated poor storage. Biocontrol efficacy and frequencies of the active ingredient genotypes decreased in the absence of annual treatment. Maize treated consecutively for 2 or 3 years had significantly (p < 0.05) less aflatoxin (92% less) in grain at harvest than untreated maize. Maize grain from treated fields subjected to simulated poor storage had significantly less (p < 0.05) aflatoxin than grain from untreated fields, regardless of application regimen. Active ingredients occurred at higher frequencies in soil and grain from treated fields than from untreated fields. The incidence of active ingredients recovered in soil was significantly correlated (r = 0.898; p < 0.001) with the incidence of active ingredients in grain, which in turn was also significantly correlated (r = -0.621, p = 0.02) with aflatoxin concentration. Although there were carry-over effects, caution should be taken when drawing recommendations about discontinuing biocontrol use. Cost-benefit analyses of single season and carry-over influences are needed to optimize use by communities of smallholder farmers in sub-Saharan Africa.

Antagonism of nonaflatoxigenic Aspergillus flavus isolated from peanuts against aflatoxigenic A. flavus growth and aflatoxin B1 production in vitro

Aspergillus section Flavi constitutes several species of opportunistic fungi, notable among them are A. flavus and A. parasiticus, capable of surviving harsh conditions and colonizing a wide range of agricultural products pre- and postharvest. Physical and chemical control methods are widely applied in order to mitigate the invasion of A. flavus in crops. However, physical control is not suitable for large scale and chemical control often leads to environmental pollution, whereas biological control offers a safer, environmentally friendly, and economical alternative. The present study aimed to investigate the antagonism of several non-aflatoxigenic A. flavus strains against the aflatoxigenic ones in vitro (semisynthetic peanut growth medium; MPA) in terms of colony growth rate and AFB1 inhibition. Different peanut concentrations were used to obtain the optimum peanut concentration in the formulated growth medium. A dual culture assay was performed to assess the antagonism of nonaflatoxigenic strains against the aflatoxigenic ones. Results revealed that 9% MPA exhibited the highest growth and AFB1 inhibition by nonaflatoxigenic strains. It was also found that different nonaflatoxigenic strains exhibited different antagonism against the aflatoxigenic ones which ranged from 11.09 ± 0.65% to 14.06 ± 0.14% for growth inhibition, and 53.97 ± 2.46% to 72.64 ± 4.54% for AFB1 inhibition. This variability could be due to the difference in antagonistic metabolites produced by different nonaflatoxigenic strains assessed in the present study. Metabolomics study to ascertain the specific metabolites that conferred the growth and aflatoxin inhibition is ongoing.

Occurrence of mycotoxins in pulses

Pulses, dry grains of the Fabaceae family used for food and feed, are particularly important agricultural products with increasing commercial and nutritional relevance. Similar to other plant commodities, pulses can be affected by fungi in the field and during postharvest. Some of these fungi produce mycotoxins, which can seriously threaten human and animal health by causing acute poisoning and chronic effects. In this review, information referring to the analysis and occurrence of these compounds in pulses is summarized. An overview of the aims pursued, and of the methodologies employed for mycotoxin analysis in the different reports is presented, followed by a comprehensive review of relevant articles on mycotoxins in pulses, categorized according to the geographical region, among other considerations. Moreover, special attention was given to the effect of climatic conditions on microorganism infestation and mycotoxin accumulation. Furthermore, the limited literature available was considered to look for possible correlations between the degree of fungal infection and the mycotoxin incidence in pulses. In addition, the potential effect of certain phenolic compounds on reducing fungi infestation and mycotoxin accumulation was reviewed with examples on beans. Emphasis was also given to a specific group of mycotoxins, the phomopsins, that mainly impact lupin. Finally, the negative consequences of mycotoxin accumulation on the physiology and development of contaminated seeds and seedlings are presented, focusing on the few reports available on pulses. Given the agricultural and nutritional potential that pulses offer for human well-being, their promotion should be accompanied by attention to food safety issues, and mycotoxins might be among the most serious threats. Practical Application: According to the manuscript template available in the website, this section is for "JFS original research manuscripts ONLY; optional". Since we are publishing in CRFSFS this requirement will not be done.

Characterization of Ugandan Endemic Aspergillus Species and Identification of Non-Aflatoxigenic Isolates for Potential Biocontrol of Aflatoxins

Acute stunting in children, liver cancer, and death often occur due to human exposure to aflatoxins in food. The severity of aflatoxin contamination depends on the type of Aspergillus fungus infecting the crops. In this study, Aspergillus species were isolated from households’ staple foods and were characterized for different aflatoxin chemotypes. The non-aflatoxigenic chemotypes were evaluated for their ability to reduce aflatoxin levels produced by aflatoxigenic A. flavus strains on maize grains. Aspergillus flavus (63%), A. tamarii (14%), and A. niger (23%) were the main species present. The A. flavus species included isolates that predominantly produced aflatoxins B1 and B2, with most isolates producing a high amount (>20 ug/µL) of aflatoxin B1 (AFB1), and a marginal proportion of them also producing G aflatoxins with a higher level of aflatoxin G1 (AFG1) than AFB1. Some non-aflatoxigenic A. tamarii demonstrated a strong ability to reduce the level of AFB1 by more than 95% when co-inoculated with aflatoxigenic A. flavus. Therefore, field evaluation of both non-aflatoxigenic A. flavus and A. tamarii would be an important step toward developing biocontrol agents for mitigating field contamination of crops with aflatoxins in Uganda.

Evaluation of endoglucanase and xylanase production by Aspergillus tamarii cultivated in agro-industrial lignocellulosic biomasses

To better understand the production of enzymes of industrial interest from microorganisms with biotechnological potential using lignocellulosic biomass, we evaluated the production of endoglucanase and xylanase from Aspergillus tamarii. CAZymes domains were evaluated in the genome, and a screening of the enzymatic potential of A. tamarii in various agricultural biomasses was done. The enzymatic profile could be associated with the biomass complexity, with increased biomass recalcitrance yielding higher activity. A time-course profile defined 48 h of cultivation as the best period for cultivating A. tamarii in sugarcane bagasse reached 12.05 IU/mg for endoglucanase and 74.86 IU/mg for xylanase. Using 0.1% (w/v) tryptone as the only nitrogen source and 12 µmol/L CuSO₄ addition had an overall positive effect on the enzymatic activity and protein production. A 2² factorial central composite design was used then to investigate the simultaneous influence of tryptone and CuSO₄ on enzyme activity. Tryptone strongly affected enzymatic activity, decreasing endoglucanase activity but increasing xylanase activity. CuSO₄ supplementation was advantageous for endoglucanases, increasing their activity, and it had a negative effect on xylanases. But overall, the experimental design increased the enzymatic activity of all biomasses used. For the clean cotton residue, the experimental design was able to reach the highest enzyme activity for endoglucanase and xylanase, with 1.195 IU/mL and 6.353 IU/mL, respectively. More experimental studies are required to investigate how the biomass induction effect impacts enzyme production.

Potential of Trichoderma spp. for Biocontrol of Aflatoxin-Producing Aspergillus flavus

The inhibitory action of 20 antagonistic Trichoderma isolates against the aflatoxigenic isolate A. flavus ITEM 9 (Af-9) and their efficacy in reducing aflatoxin formation in vitro were examined. Production of metabolites with inhibitory effect by the Trichoderma isolates was also investigated. Antagonistic effect against Af-9 was assessed by inhibition of radial growth of the colonies and by fungal interactions in dual confrontation tests. A total of 8 out of 20 isolates resulted in a significant growth inhibition of 3-day-old cultures of Af-9, ranging from 13% to 65%. A total of 14 isolates reduced significantly the aflatoxin B₁ (AfB₁) content of 15-day-old Af-9 cultures; 4 were ineffective, and 2 increased AfB₁. Reduction of AfB₁ content was up to 84.9% and 71.1% in 7- and 15-day-old cultures, respectively. Since the inhibition of Af-9 growth by metabolites of Trichoderma was not necessarily associated with inhibition of AfB₁ production and vice versa, we investigated the mechanism of reduction of AfB₁ content at the molecular level by examining two strains: one (T60) that reduced both growth and mycotoxin content; and the other (T44) that reduced mycotoxin content but not Af-9 growth. The expression analyses for the two regulatory genes aflR and aflS, and the structural genes aflA, aflD, aflO and aflQ of the aflatoxin biosynthesis cluster indicated that neither strain was able to downregulate the aflatoxin synthesis, leading to the conclusion that the AfB₁ content reduction by these Trichoderma strains was based on other mechanisms, such as enzyme degradation or complexation. Although further studies are envisaged to identify the metabolites involved in the biocontrol of A. flavus and prevention of aflatoxin accumulation, as well as for assessment of the efficacy under controlled and field conditions, Trichoderma spp. qualify as promising agents and possible alternative options to other biocontrol agents already in use.

Distribution of Aspergillus Fungi and Recent Aflatoxin Reports, Health Risks, and Advances in Developments of Biological Mitigation Strategies in China

Aflatoxins (AFs) are secondary metabolites that represent serious threats to human and animal health. They are mainly produced by strains of the saprophytic fungus Aspergillus flavus, which are abundantly distributed across agricultural commodities. AF contamination is receiving increasing attention by researchers, food producers, and policy makers in China, and several interesting review papers have been published, that mainly focused on occurrences of AFs in agricultural commodities in China. The goal of this review is to provide a wider scale and up-to-date overview of AF occurrences in different agricultural products and of the distribution of A. flavus across different food and feed categories and in Chinese traditional herbal medicines in China, for the period 2000-2020. We also highlight the health impacts of chronic dietary AF exposure, the recent advances in biological AF mitigation strategies in China, and recent Chinese AF standards.

Competency of Clove and Cinnamon Essential Oil Fumigation against Toxigenic and Atoxigenic Aspergillus flavus Isolates

Aspergillus flavus is a frequent contaminant of maize grain. We isolated this fungus, determined the colony morphology and species (by internal transcribed spacer sequencing) and measured the aflatoxin content. The selected A. flavus fungi were placed into two groups, toxigenic and atoxigenic; both appeared similar morphologically, except that the atoxigenic group lacked sclerotia. An essential oil fumigation test with clove and cinnamon oils as antifungal products was performed on fungal conidial discs and fungal colonies in Petri plates. Cinnamon oil at 2.5 to 5.0 μL/plate markedly inhibited the mycelial growth from conidial discs of both strains, whereas clove oil showed less activity. The oils had different effects on fungal mycelia. The higher clove fumigation doses of 10.0 to 20.0 μL/plate controlled fungal growth, while cinnamon oil caused less inhibition. Compared with atoxigenic groups, toxigenic A. flavus responded stably. Within abnormal A. flavus hyphae, the essential oils degenerated the hyphal morphology, resulting in exfoliated flakes and shrinkage, which were related to fungal membrane injury and collapse of vacuoles and phialide. The treatments, especially those with cinnamon oil, increased the electroconductivity, which suggested a weak mycelium membrane structure. Moreover, the treatments with essential oils reduced the ergosterol content in mycelia and the aflatoxin accumulation in the culture broth. The fumigations with clove and cinnamon oils inhibited the development of both conidia and colonies of A. flavus in dose-dependent manners.

Temperature Influences on Interactions Among Aflatoxigenic Species of Aspergillus Section Flavi During Maize Colonization

Fungal species within Aspergillus section Flavi contaminate food and feed with aflatoxins. These toxic fungal metabolites compromise human and animal health and disrupt trade. Genotypically and phenotypically diverse species co-infect crops, but temporal and spatial variation in frequencies of different lineages suggests that environmental factors such as temperature may influence structure of aflatoxin-producing fungal communities. Furthermore, though most species within Aspergillus section Flavi produce sclerotia, divergent sclerotial morphologies (small or S-type sclerotia vs. large or L-type sclerotia) and differences in types and quantities of aflatoxins produced suggest lineages are adapted to different life strategies. Temperature is a key parameter influencing pre- and post-harvest aflatoxin contamination of crops. We tested the hypothesis that species of aflatoxin-producing fungi that differ in sclerotial morphology will vary in competitive ability and that outcomes of competition and aflatoxin production will be modulated by temperature. Paired competition experiments between highly aflatoxigenic S-type species (A. aflatoxiformans and Lethal Aflatoxicosis Fungus) and L-type species (A. flavus L morphotype and A. parasiticus) were conducted on maize kernels at 25 and 30°C. Proportions of each isolate growing within and sporulating on kernels were measured using quantitative pyrosequencing. At 30°C, S-type fungi were more effective at host colonization compared to L-type isolates. Total aflatoxins and the proportion of B vs. G aflatoxins were greater at 30°C compared to 25°C. Sporulation by L-type isolates was reduced during competition with S-type fungi at 30°C, while relative quantities of conidia produced by S-type species either increased or did not change during competition. Results indicate that both species interactions and temperature can shape population structure of Aspergillus section Flavi, with warmer temperatures favoring growth and dispersal of highly toxigenic species with S-type sclerotia.

Distribution of active ingredients of a commercial aflatoxin biocontrol product in naturally occurring fungal communities across Kenya

Human populations in Kenya are repeatedly exposed to dangerous aflatoxin levels through consumption of contaminated crops. Biocontrol with atoxigenic Aspergillus flavus is an effective method for preventing aflatoxin in crops. Although four atoxigenic A. flavus isolates (C6E, E63I, R7H and R7K) recovered from maize produced in Kenya are registered as active ingredients for a biocontrol product (Aflasafe KE01) directed at preventing contamination, natural distributions of these four genotypes prior to initiation of commercial use have not been reported. Distributions of the active ingredients of KE01 based on haplotypes at 17 SSR loci are reported. Incidences of the active ingredients and closely related haplotypes were determined in soil collected from 629 maize fields in consecutive long and short rains seasons of 2012. The four KE01 haplotypes were among the top ten most frequent. Haplotype H-1467 of active ingredient R7K was the most frequent and widespread haplotype in both seasons and was detected in the most soils (3.8%). The four KE01 haplotypes each belonged to large clonal groups containing 27-46 unique haplotypes distributed across multiple areas and in 21% of soils. Each of the KE01 haplotypes belonged to a distinct vegetative compatibility group (VCG), and all A. flavus with haplotypes matching a KE01 active ingredient belonged to the same VCG as the matching active ingredient as did all A. flavus haplotypes differing at only one SSR locus. Persistence of the KE01 active ingredients in Kenyan agroecosystems is demonstrated by detection of identical SSR haplotypes six years after initial isolation. The data provide baselines for assessing long-term influences of biocontrol applications in highly vulnerable production areas of Kenya.

Biocontrol of Aflatoxins Using Non-Aflatoxigenic Aspergillus flavus: A Literature Review

Aflatoxins (AFs) are mycotoxins, predominantly produced by Aspergillus flavus, A. parasiticus, A. nomius, and A. pseudotamarii. AFs are carcinogenic compounds causing liver cancer in humans and animals. Physical and biological factors significantly affect AF production during the pre-and post-harvest time. Several methodologies have been developed to control AF contamination, yet; they are usually expensive and unfriendly to the environment. Consequently, interest in using biocontrol agents has increased, as they are convenient, advanced, and friendly to the environment. Using non-aflatoxigenic strains of A. flavus (AF⁻) as biocontrol agents is the most promising method to control AFs’ contamination in cereal crops. AF⁻ strains cannot produce AFs due to the absence of polyketide synthase genes or genetic mutation. AF⁻ strains competitively exclude the AF⁺ strains in the field, giving an extra advantage to the stored grains. Several microbiological, molecular, and field-based approaches have been used to select a suitable biocontrol agent. The effectiveness of biocontrol agents in controlling AF contamination could reach up to 99.3%. Optimal inoculum rate and a perfect time of application are critical factors influencing the efficacy of biocontrol agents.

Aflasafe SN01 is the First Biocontrol Product Approved for Aflatoxin Mitigation in Two Nations, Senegal and The Gambia

Aflatoxin contamination is caused by Aspergillus flavus and closely related fungi. In The Gambia, aflatoxin contamination of groundnut and maize, two staple and economically important crops, is common. Groundnut and maize consumers are chronically exposed to aflatoxins, sometimes at alarming levels, and this has severe consequences on their health and productivity. Aflatoxin contamination also impedes commercialization in local and international premium markets. In neighboring Senegal, an aflatoxin biocontrol product containing four atoxigenic isolates of A. flavus, Aflasafe SN01, has been registered and is approved for commercial use in groundnut and maize. We detected that the four genotypes composing Aflasafe SN01 are also native to The Gambia. The biocontrol product was tested during two years in 129 maize and groundnut fields and compared with corresponding untreated fields cropped by smallholder farmers in The Gambia. Treated crops contained up to 100% less aflatoxins than untreated crops. A large portion of the crops could have been commercialized in premium markets due to the low aflatoxin content (in many cases no detectable aflatoxins), both at harvest and after storage. Substantial aflatoxin reductions were also achieved when commercially produced groundnut received treatment. Here we report for the first time the use and effectiveness of an aflatoxin biocontrol product registered for use in two nations. With the current scale-out and -up efforts of Aflasafe SN01, a large number of farmers, consumers, and traders in The Gambia and Senegal will obtain health, income, and trade benefits.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Sensitivity of Aspergillus flavus Isolates from Peanut Seeds in Georgia to Azoxystrobin, a Quinone outside Inhibitor (QoI) Fungicide

Aspergillus flavus infects peanuts and produces a mycotoxin called aflatoxin, a potent human carcinogen. In infected peanuts, it can also affect peanut seed quality by causing seed rot and reducing seed viability, resulting in low germination. In 2020, peanut seeds in Georgia had lower than expected germination and a high frequency of A. flavus contamination. A total of 76 Aspergillus isolates were collected from seven seed lots and their identity and in vitro reaction to QoI (quinone outside inhibitor) fungicide (azoxystrobin) were studied. The isolates were confirmed as A. flavus by morphological characteristics and a PCR (polymerase chain reaction)-based method using species-specific primers. In vitro, these isolates were tested for sensitivity to azoxystrobin. The mean EC50 values ranged from 0.12 to 297.22 μg/mL, suggesting that some isolates were resistant or tolerate to this fungicide. The sequences of cytochrome b gene from these isolates were compared and a single nucleotide mutation (36.8% isolates) was found as Cyt B G143A, which was associated with the total resistance to the QoIs. Another single mutation (15.8% isolates) was also observed as Cyt B F129L, which had been documented for QoI resistance. Therefore, a new major single mutation was detected in the A. flavus natural population in this study, and it might explain the cause of the bad seed quality in 2020. The high frequency of this new single nucleotide mutation exists in the natural population of A. flavus and results in the ineffectiveness of using azoxystrobin seed treatment. New seed treatment fungicides are needed.

Phenotypic Differentiation of Two Morphologically Similar Aflatoxin-Producing Fungi from West Africa

Aflatoxins (AF) are hepatocarcinogenic metabolites produced by several Aspergillus species. Crop infection by these species results in aflatoxin contamination of cereals, nuts, and spices. Etiology of aflatoxin contamination is complicated by mixed infections of multiple species with similar morphology and aflatoxin profiles. The current study investigates variation in aflatoxin production between two morphologically similar species that co-exist in West Africa, A. aflatoxiformans and A. minisclerotigenes. Consistent distinctions in aflatoxin production during liquid fermentation were discovered between these species. The two species produced similar concentrations of AFB₁ in defined media with either urea or ammonium as the sole nitrogen source. However, production of both AFB₁ and AFG₁ were inhibited (p < 0.001) for A. aflatoxiformans in a yeast extract medium with sucrose. Although production of AFG₁ by both species was similar in urea, A. minisclerotigenes produced greater concentrations of AFG₁ in ammonium (p = 0.039). Based on these differences, a reliable and convenient assay for differentiating the two species was designed. This assay will be useful for identifying specific etiologic agents of aflatoxin contamination episodes in West Africa and other regions where the two species are sympatric, especially when phylogenetic analyses based on multiple gene segments are not practical.

Founder events influence structures of Aspergillus flavus populations

In warm regions, agricultural fields are occupied by complex Aspergillus flavus communities composed of isolates in many vegetative compatibility groups (VCGs) with varying abilities to produce highly toxic, carcinogenic aflatoxins. Aflatoxin contamination is reduced with biocontrol products that enable atoxigenic isolates from atoxigenic VCGs to dominate the population. Shifts in VCG frequencies similar to those caused by the introduction of biocontrol isolates were detected in Sonora, Mexico, where biocontrol is not currently practiced. The shifts were attributed to founder events. Although VCGs reproduce clonally, significant diversity exists within VCGs. Simple sequence repeat (SSR) fingerprinting revealed that increased frequencies of VCG YV150 involved a single haplotype. This is consistent with a founder event. Additionally, great diversity was detected among 82 YV150 isolates collected over 20 years across Mexico and the United States. Thirty-six YV150 haplotypes were separated into two populations by Structure and SplitsTree analyses. Sixty-five percent of isolates had MAT1-1 and belonged to one population. The remaining had MAT1-2 and belonged to the second population. SSR alleles varied within populations, but recombination between populations was not detected despite co-occurrence at some locations. Results suggest that YV150 isolates with opposite mating-type have either strongly restrained or lost sexual reproduction among themselves.

Molecular Analysis of S-morphology Aflatoxin Producers From the United States Reveals Previously Unknown Diversity and Two New Taxa

Aflatoxins are highly toxic carcinogens that detrimentally influence profitability of agriculture and the health of humans and domestic animals. Several phylogenetically distinct fungi within Aspergillus section Flavi have S-morphology (average sclerotial size < 400 μm), and consistently produce high concentrations of aflatoxins in crops. S-morphology fungi have been implicated as important etiologic agents of aflatoxin contamination in the United States (US), but little is known about the diversity of these fungi. The current study characterized S-morphology fungi (n = 494) collected between 2002 and 2017, from soil and maize samples, in US regions where aflatoxin contamination is a perennial problem. Phylogenetic analyses based on sequences of the calmodulin (1.9 kb) and nitrate reductase (2.1 kb) genes resolved S-morphology isolates from the US into four distinct clades: (1) Aspergillus flavus S-morphotype (89.7%); (2) Aspergillus agricola sp. nov. (2.4%); (3) Aspergillus texensis (2.2%); and (4) Aspergillus toxicus sp. nov. (5.7%). All four S-morphology species produced high concentrations of aflatoxins in maize at 25, 30, and 35°C, but only the A. flavus S-morphotype produced unacceptable aflatoxin concentrations at 40°C. Genetic typing of A. flavus S isolates using 17 simple sequence repeat markers revealed high genetic diversity, with 202 haplotypes from 443 isolates. Knowledge of the occurrence of distinct species and haplotypes of S-morphology fungi that are highly aflatoxigenic under a range of environmental conditions may provide insights into the etiology, epidemiology, and management of aflatoxin contamination in North America.

The Atoxigenic Biocontrol Product Aflasafe SN01 Is a Valuable Tool to Mitigate Aflatoxin Contamination of Both Maize and Groundnut Cultivated in Senegal

Aflatoxin contamination of groundnut and maize infected by Aspergillus section Flavi fungi is common throughout Senegal. The use of biocontrol products containing atoxigenic Aspergillus flavus strains to reduce crop aflatoxin content has been successful in several regions, but no such products are available in Senegal. The biocontrol product Aflasafe SN01 was developed for use in Senegal. The four active ingredients of Aflasafe SN01 are atoxigenic A. flavus genotypes native to Senegal and distinct from active ingredients used in other biocontrol products. Efficacy tests on groundnut and maize in farmers' fields were carried out in Senegal during the course of 5 years. Active ingredients were monitored with vegetative compatibility analyses. Significant (P < 0.05) displacement of aflatoxin producers occurred in all years, districts, and crops. In addition, crops from Aflasafe SN01-treated fields contained significantly (P < 0.05) fewer aflatoxins both at harvest and after storage. Most crops from treated fields contained aflatoxin concentrations permissible in both local and international markets. Results suggest that Aflasafe SN01 is an effective tool for aflatoxin mitigation in groundnut and maize. Large-scale use of Aflasafe SN01 should provide health, trade, and economic benefits for Senegal.[Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Variation in Occurrence and Aflatoxigenicity of Aspergillus flavus from Two Climatically Varied Regions in Kenya

Aflatoxins are carcinogenic chemical metabolites produced by Aspergillus spp. of the section Flavi. In Kenya, Aspergillus flavus is the most prevalent and has been associated with several acute and chronic aflatoxin outbreaks in the past. In this study, we evaluated the occurrence of A. flavus in soils from two agro-ecological regions with contrasting climatic conditions, aflatoxin contamination histories and cropping systems. Aspergillus spp. were first isolated from soils before the identification and determination of their aflatoxigenicity. Further, we determined the occurrence of Pseudomonas and Bacillus spp. in soils from the two regions. These bacterial species have long been associated with biological control of several plant pathogens including Aspergillus spp. Our results show that A. flavus occurred widely and produced comparatively higher total aflatoxin levels in all (100%) study sites from the eastern to the western regions of Kenya. For the western region, A. flavus was detected in 4 locations (66.7%) that were previously under maize cultivation with the isolates showing low aflatoxigenicity. A. flavus was not isolated from soils under sugarcane cultivation. Distribution of the two bacterial species varied across the regions but we detected a weak relationship between occurrence of bacterial species and A. flavus. We discuss these findings in the context of the influence of climate, microbial profiles, cropping systems and applicability in the deployment of biological control remedies against aflatoxin contamination.

Control of Aflatoxigenic Molds by Antagonistic Microorganisms: Inhibitory Behaviors, Bioactive Compounds, Related Mechanisms, and Influencing Factors

Aflatoxin contamination has been causing great concern worldwide due to the major economic impact on crop production and their toxicological effects to human and animals. Contamination can occur in the field, during transportation, and also in storage. Post-harvest contamination usually derives from the pre-harvest infection of aflatoxigenic molds, especially aflatoxin-producing Aspergilli such as Aspergillusflavus and A. parasiticus. Many strategies preventing aflatoxigenic molds from entering food and feed chains have been reported, among which biological control is becoming one of the most praised strategies. The objective of this article is to review the biocontrol strategy for inhibiting the growth of and aflatoxin production by aflatoxigenic fungi. This review focuses on comparing inhibitory behaviors of different antagonistic microorganisms including various bacteria, fungi and yeasts. We also reviewed the bioactive compounds produced by microorganisms and the mechanisms leading to inhibition. The key factors influencing antifungal activities of antagonists are also discussed in this review.

"Ground-Truthing" Efficacy of Biological Control for Aflatoxin Mitigation in Farmers' Fields in Nigeria: From Field Trials to Commercial Usage, a 10-Year Study

In sub-Saharan Africa (SSA), diverse fungi belonging to Aspergillus section Flavi frequently contaminate staple crops with aflatoxins. Aflatoxins negatively impact health, income, trade, food security, and development sectors. Aspergillus flavus is the most common causal agent of contamination. However, certain A. flavus genotypes do not produce aflatoxins (i.e., are atoxigenic). An aflatoxin biocontrol technology employing atoxigenic genotypes to limit crop contamination was developed in the United States. The technology was adapted and improved for use in maize and groundnut in SSA under the trademark Aflasafe. Nigeria was the first African nation for which an aflatoxin biocontrol product was developed. The current study includes tests to assess biocontrol performance across Nigeria over the past decade. The presented data on efficacy spans years in which a relatively small number of maize and groundnut fields (8-51 per year) were treated through use on circa 36,000 ha in commercially-produced maize in 2018. During the testing phase (2009-2012), fields treated during one year were not treated in the other years while during commercial usage (2013-2019), many fields were treated in multiple years. This is the first report of a large-scale, long-term efficacy study of any biocontrol product developed to date for a field crop. Most (>95%) of 213,406 tons of maize grains harvested from treated fields contained <20 ppb total aflatoxins, and a significant proportion (>90%) contained <4 ppb total aflatoxins. Grains from treated plots had preponderantly >80% less aflatoxin content than untreated crops. The frequency of the biocontrol active ingredient atoxigenic genotypes in grains from treated fields was significantly higher than in grains from control fields. A higher proportion of grains from treated fields met various aflatoxin standards compared to grains from untreated fields. Results indicate that efficacy of the biocontrol product in limiting aflatoxin contamination is stable regardless of environment and cropping system. In summary, the biocontrol technology allows farmers across Nigeria to produce safer crops for consumption and increases potential for access to premium markets that require aflatoxin-compliant crops.

Aflatoxin-producing fungi associated with pre-harvest maize contamination in Uganda

Maize is an important staple crop for the majority of the population in Uganda. However, in tropical and subtropical climates, maize is frequently contaminated with aflatoxins, a group of cancer-causing and immuno-suppressive mycotoxins produced by Aspergillus section Flavi fungi. In Uganda, there is limited knowledge about the causal agents of aflatoxin contamination. The current study determined both the aflatoxin levels in pre-harvest maize across Uganda and the structures of communities of aflatoxin-producing fungi associated with the maize. A total of 256 pre-harvest maize samples were collected from 23 major maize-growing districts in eight agro-ecological zones (AEZ). Maize aflatoxin content ranged from 0 to 3760 ng/g although only around 5% for Ugandan thresholds. For EU it is about 16% of the samples contained aflatoxin concentrations above tolerance thresholds. A total of 3105 Aspergillus section Flavi isolates were recovered and these were dominated by the A. flavus L morphotype (89.4%). Densities of aflatoxin-producing fungi were negatively correlated with elevation. Farming systems and climatic conditions of the AEZ are thought to have influenced communities' structure composition. Fungi from different AEZ varied significantly in aflatoxin-producing abilities and several atoxigenic genotypes were identified. The extremely high aflatoxin concentrations detected in some of the studied regions indicate that management strategies should be urgently designed for use at the pre-harvest stage. Atoxigenic genotypes detected across Uganda could serve as aflatoxin biocontrol agents to reduce crop contamination from fields conditions and throughout the maize value chain.

An atoxigenic L-strain of Aspergillus flavus (Eurotiales: Trichocomaceae) is pathogenic to the coffee twig borer, Xylosandrus compactus (Coleoptera: Curculionidea: Scolytinae)

This study isolated and evaluated virulence of fungal entomopathogens of Xylosandrus compactus - an important pest of Robusta coffee in Sub-Saharan Africa. A survey was conducted in five farming systems in Uganda to isolate entomopathogens associated with X. compactus. Four fungal isolates were screened for virulence against X. compactus in the laboratory at 1 × 10⁷ conidia ml^-1 where an atoxigenic L-strain of A. flavus killed 70%-100% of all stages of X. compactus compared with other unidentified isolates which caused 20%-70% mortalities. The time taken by A. flavus to kill 50% of X. compactus eggs, larvae, pupae and adults in the laboratory was 2-3 days; whereas the other unidentified fungal isolates took 4-7 days. The concentrations of A. flavus that killed 50% of different stages of X. compactus were 5 × 10⁵ , 12 × 10⁵ , 17 × 10⁵ and 30 × 10⁵ conidia ml^-1 for larvae, eggs, pupae and adults respectively. A formulation of A. flavus in oil caused higher mortalities of X. compactus larvae, pupae and adults in the field (71%-79%) than its formulation in water (33%-47%). The atoxigenic strain of A. flavus could therefore be developed into a safe biopesticide against X. compactus.

Aflatoxin in Chili Peppers in Nigeria: Extent of Contamination and Control Using Atoxigenic Aspergillus flavus Genotypes as Biocontrol Agents

Across sub-Saharan Africa, chili peppers are fundamental ingredients of many traditional dishes. However, chili peppers may contain unsafe aflatoxin concentrations produced by Aspergillus section Flavi fungi. Aflatoxin levels were determined in chili peppers from three states in Nigeria. A total of 70 samples were collected from farmers’ stores and local markets. Over 25% of the samples contained unsafe aflatoxin concentrations. The chili peppers were associated with both aflatoxin producers and atoxigenic Aspergillus flavus genotypes. Efficacy of an atoxigenic biocontrol product, Aflasafe, registered in Nigeria for use on maize and groundnut, was tested for chili peppers grown in three states. Chili peppers treated with Aflasafe accumulated significantly less aflatoxins than nontreated chili peppers. The results suggest that Aflasafe is a valuable tool for the production of safe chili peppers. Use of Aflasafe in chili peppers could reduce human exposure to aflatoxins and increase chances to commercialize chili peppers in premium local and international markets. This is the first report of the efficacy of any atoxigenic biocontrol product for controlling aflatoxin in a spice crop.

Dual culture of atoxigenic and toxigenic strains of Aspergillus flavus to gain insight into repression of aflatoxin biosynthesis and fungal interaction

Application of atoxigenic strains to compete against toxigenic strains of Aspergillus flavus strains has emerged as one of the practical strategies for reducing aflatoxin contamination in corn, peanut, and tree nuts. The actual mechanism that results in aflatoxin reduction is not fully understood. Real-time RT-PCR and relative quantification of gene expression protocol were applied to elucidate the molecular mechanism. Transcriptional analyses of aflatoxin biosynthetic gene cluster in dual culture of toxigenic and atoxigenic A. flavus strains were carried out. Six targeted genes, aflR, aflJ, omtA, ordA, pksA, and vbs, were downregulated to variable levels depending on paired strains of toxigenic and atoxigenic A. flavus. Consistent with the decreased gene expression levels, the aflatoxin concentrations in dual cultures were reduced significantly in comparison with toxigenic cultures. Fluorescent images showed fungal hyphae in dual culture displayed green fluorescent, and contacts of live hyphae were seen. A coconut agar plate assay was used to show that toxigenic A. flavus colony produced blue fluorescence under long UV exposure, suggesting that aflatoxin is exported outside fungal hyphae. Furthermore, the assay was applied to demonstrate the potential role of thigmo-regulation in fungal interaction.

Population Subdivision and the Frequency of Aflatoxigenic Isolates in Aspergillus flavus in the United States

Consumption of food contaminated with aflatoxin, from crops infected by Aspergillus flavus, is associated with acute toxicosis, cancer, and stunted growth. Although such contamination is more common in the lower latitudes of the United States, it is unclear whether this pattern is associated with differences in the relative frequencies of aflatoxigenic individuals of A. flavus. To determine whether the frequency of the aflatoxin-producing ability of A. flavus increases as latitude decreases, we sampled 281 isolates from field soils in two north-south transects in the United States and tested them for aflatoxin production. We also genotyped 161 isolates using 10 microsatellite markers to assess population structure. Although the population density of A. flavus was highest at lower latitudes, there was no difference in the frequency of aflatoxigenic A. flavus isolates in relation to latitude. We found that the U.S. population of A. flavus is subdivided into two genetically differentiated subpopulations that are not associated with the chemotype or geographic origin of the isolates. The two populations differ markedly in allelic and genotypic diversity. The less diverse population is more abundant and may represent a clonal lineage derived from the more diverse population. Overall, increased aflatoxin contamination in lower latitudes may be explained partially by differences in the population density of A. flavus, not genetic population structure.

Atoxigenic Aspergillus flavus Isolates Endemic to Almond, Fig, and Pistachio Orchards in California with Potential to Reduce Aflatoxin Contamination in these Crops

In California, aflatoxin contamination of almond, fig, and pistachio has become a serious problem in recent years due to long periods of drought and probably other climatic changes. The atoxigenic biocontrol product Aspergillus flavus AF36 has been registered for use to limit aflatoxin contamination of pistachio since 2012 and for use in almond and fig since 2017. New biocontrol technologies employ multiple atoxigenic genotypes because those provide greater benefits than using a single genotype. Almond, fig, and pistachio industries would benefit from a multi-strain biocontrol technology for use in these three crops. Several A. flavus vegetative compatibility groups (VCGs) associated with almond, fig, and pistachio composed exclusively of atoxigenic isolates, including the VCG to which AF36 belongs to, YV36, were previously characterized in California. Here, we report additional VCGs associated with either two or all three crops. Representative isolates of 12 atoxigenic VCGs significantly (P < 0.001) reduced (>80%) aflatoxin accumulation in almond and pistachio when challenged with highly toxigenic isolates of A. flavus and A. parasiticus under laboratory conditions. Isolates of the evaluated VCGs, including AF36, constitute valuable endemic, well-adapted, and efficient germplasm to design a multi-crop, multi-strain biocontrol strategy for use in tree crops in California. Availability of such a strategy would favor long-term atoxigenic A. flavus communities across the affected areas of California, and this would result in securing domestic and export markets for the nut crop and fig farmer industries and, most importantly, health benefits to consumers.

Secondary Metabolite Dereplication and Phylogenetic Analysis Identify Various Emerging Mycotoxins and Reveal the High Intra-Species Diversity in Aspergillus flavus

Aspergillus flavus is one of the most important mycotoxigenic species from the genus Aspergillus, due to its ability to synthesize the potent hepatocarcinogen, aflatoxin B₁. Moreover, this fungus is capable of producing several other toxic metabolites from the class of indole-tetramates, non-ribosomal peptides, and indole-diterpenoids. Populations of A. flavus are characterized by considerable diversity in terms of morphological, functional and genetic features. Although for many years A. flavus was considered an asexual fungus, researchers have shown evidence that at best these fungi can exhibit a predominantly asexual existence. We now know that A. flavus contains functional genes for mating, uncovering sexuality as potential contributor for its diversification. Based on our results, we reconfirm that A. flavus is a predominant producer of B-type aflatoxins. Moreover, this fungus can decisively produce AFM₁ and AFM₂. We did not observe any clear relationship between mating-type genes and particular class of metabolites, probably other parameters such as sexual/asexual ratio should be investigated. A dynamic secondary metabolism was found also in strains intended to be used as biocontrol agents. In addition we succeeded to provide mass spectrometry fragmentation spectra for the most important classes of A. flavus metabolites, which will serve as identification cards for future studies. Both, metabolic and phylogenetic analysis proved a high intra-species diversity for A. flavus. These findings contribute to our understanding about the diversity of Aspergillus section Flavi species, raising the necessity for polyphasic approaches (morphological, metabolic, genetic, etc.) when dealing with this type of complex group of species.

Transcriptional Regulation of Aflatoxin Biosynthesis and Conidiation in Aspergillus flavus by Wickerhamomyces anomalus WRL-076 for Reduction of Aflatoxin Contamination

Aspergillus flavus is a ubiquitous saprophytic fungus found in soils across the world. The fungus is the major producer of aflatoxin (AF) B₁, which is toxic and a potent carcinogen to humans. Aflatoxin B₁ (AFB₁) is often detected in agricultural crops such as corn, peanut, almond, and pistachio. It is a serious and recurrent problem and causes substantial economic losses. Wickerhamomyces anomalus WRL-076 was identified as an effective biocontrol yeast against A. flavus. In this study, the associated molecular mechanisms of biocontrol were investigated. We found that the expression levels of eight genes, aflR, aflJ, norA, omtA, omtB, pksA, vbs, and ver-1 in the aflatoxin biosynthetic pathway cluster were suppressed. The decreases ranged from several to 10,000 fold in fungal samples co-cultured with W. anomalus. Expression levels of conidiation regulatory genes brlA, abaA, and wetA as well as sclerotial regulatory gene (sclR) were all down regulated. Consistent with the decreased gene expression levels, aflatoxin concentrations in cultural medium were reduced to barely detectable. Furthermore, fungal biomass and conidial number were significantly reduced by 60% and more than 95%, respectively. The results validate the biocontrol efficacy of W. anomalus WRL-076 observed in the field experiments.

Comparative Genomics of Aspergillus flavus S and L Morphotypes Yield Insights into Niche Adaptation

Aspergillus flavus, the primary causal agent for aflatoxin contamination on crops, consists of isolates with two distinct morphologies: isolates of the S morphotype produce numerous small sclerotia and lower numbers of conidia while isolates of the L morphotype produce fewer large sclerotia and abundant conidia. The morphotypes also differ in aflatoxin production with S isolates consistently producing high concentrations of aflatoxin, whereas L isolates range from atoxigenic to highly toxigenic. The production of abundant sclerotia by the S morphotype suggests adaptation for long-term survival in the soil, whereas the production of abundant conidia by the L morphotype suggests adaptation for aerial dispersal to the phyllosphere. To identify genomic changes that support differential niche adaption, the sequences of three S and three L morphotype isolates were compared. Differences in genome structure and gene content were identified between the morphotypes. A >530 kb inversion between the morphotypes affect a secondary metabolite gene cluster and a cutinase gene. The morphotypes also differed in proteins predicted to be involved in carbon/nitrogen metabolism, iron acquisition, antimicrobial defense, and evasion of host immunity. The S morphotype genomes contained more intact secondary metabolite clusters indicating there is higher selection pressure to maintain secondary metabolism in the soil and that it is not limited to aflatoxin production. The L morphotype genomes were enriched in amino acid transporters, suggesting efficient nitrogen transport may be critical in the nutrient limited phyllosphere. These findings indicate the genomes of the two morphotypes differ beyond developmental genes and have diverged as they adapted to their respective niches.

Inferring the presence of aflatoxin-producing Aspergillus flavus strains using RNA sequencing and electronic probes as a transcriptomic screening tool

E-probe Diagnostic for Nucleic acid Analysis (EDNA) is a bioinformatic tool originally developed to detect plant pathogens in metagenomic databases. However, enhancements made to EDNA increased its capacity to conduct hypothesis directed detection of specific gene targets present in transcriptomic databases. To target specific pathogenicity factors used by the pathogen to infect its host or other targets of interest, e-probes need to be developed for transcripts related to that function. In this study, EDNA transcriptomics (EDNAtran) was developed to detect the expression of genes related to aflatoxin production at the transcriptomic level. E-probes were designed from genes up-regulated during A. flavus aflatoxin production. EDNAtran detected gene transcripts related to aflatoxin production in a transcriptomic database from corn, where aflatoxin was produced. The results were significantly different from e-probes being used in the transcriptomic database where aflatoxin was not produced (atoxigenic AF36 strain and toxigenic AF70 in Potato Dextrose Broth).

Aspergillus flavus resident in Kenya: High genetic diversity in an ancient population primarily shaped by clonal reproduction and mutation-driven evolution

Aspergillus flavus has long been considered to be an asexual species. Although a sexual stage was recently reported for this species from in vitro studies, the amount of recombination ongoing in natural populations and the genetic distance across which meiosis occurs is largely unknown. In the current study, genetic diversity, reproduction and evolution of natural A. flavus populations endemic to Kenya were examined. A total of 2744 isolates recovered from 629 maize-field soils across southern Kenya in two consecutive seasons were characterized at 17 SSR loci, revealing high genetic diversity (9-72 alleles/locus and 2140 haplotypes). Clonal reproduction and persistence of clonal lineages predominated, with many identical haplotypes occurring in multiple soil samples and both seasons. Genetic analyses predicted three distinct lineages with linkage disequilibrium and evolutionary relationships among haplotypes within each lineage suggesting mutation-driven evolution followed by clonal reproduction. Low genetic differentiation among adjacent communities reflected frequent short distance dispersal.

Characterization of Argentinian Endemic Aspergillus flavus Isolates and Their Potential Use as Biocontrol Agents for Mycotoxins in Maize

Maize (Zea mays L.) is a highly valuable crop in Argentina, frequently contaminated with the mycotoxins produced by Aspergillus flavus. Biocontrol products formulated with atoxigenic (nontoxic) strains of this fungal species are well known as an effective method to reduce this contamination. In the present study, 83 A. flavus isolates from two maize regions of Argentina were characterized and evaluated for their ability to produce or lack of producing mycotoxins in order to select atoxigenic strains to be used as potential biocontrol agents (BCA). All of the isolates were tested for aflatoxin and cyclopiazonic acid (CPA) production in maize kernels and a liquid culture medium. Genetic diversity of the nonaflatoxigenic isolates was evaluated by analysis of vegetative compatibility groups (VCG) and confirmation of deletions in the aflatoxin biosynthesis cluster. Eight atoxigenic isolates were compared for their ability to reduce aflatoxin and CPA contamination in maize kernels in coinoculation tests. The A. flavus population was composed of 32% aflatoxin and CPA producers and 52% CPA producers, and 16% was determined as atoxigenic. All of the aflatoxin producer isolates also produced CPA. Aflatoxin and CPA production was significantly higher in maize kernels than in liquid medium. The 57 nonaflatoxigenic strains formed six VCG, with AM1 and AM5 being the dominant groups, with a frequency of 58 and 35%, respectively. In coinoculation experiments, all of the atoxigenic strains reduced aflatoxin from 54 to 83% and CPA from 60 to 97%. Members of group AM1 showed a greater aflatoxin reduction than members of AM5 (72 versus 66%) but no differences were detected in CPA production. Here, we described for the first time atoxigenic isolates of A. flavus that show promise to be used as BCA in maize crops in Argentina. This innovating biological control approach should be considered, developed further, and used by the maize industry to preserve the quality properties and food safety of maize kernels in Argentina.

Characterization and competitive ability of non-aflatoxigenic Aspergillus flavus isolated from the maize agro-ecosystem in Argentina as potential aflatoxin biocontrol agents

Aspergillus flavus is an opportunistic pathogen and may produce aflatoxins in maize, one of the most important crops in Argentina. A promising strategy to reduce aflatoxin accumulation is the biological control based on competitive exclusion. In order to select potential biocontrol agents among isolates from the maize growing region in Argentina, a total of 512 A. flavus strains were isolated from maize kernels and soil samples. Thirty-six per cent of the isolates from maize kernels did not produce detectable levels of aflatoxins, while 73% of the isolates from soil were characterized as non-aflatoxin producers. Forty percent and 49% of the isolates from maize kernels and soil samples, respectively, were not producers of cyclopiazonic acid (CPA). Sclerotia morphology was evaluated using Czapek Dox media. Eighty-six per cent of the isolates from maize kernels and 85% of the isolates from soil samples were L sclerotia morphotype (average diameter > 400 μm). The remaining isolates did not produce sclerotia. All isolates had MAT 1-1 idiomorph. The competitive ability of 9 non aflatoxigenic strains, 4 CPA(+) and 5 CPA(-), was evaluated in co-inoculations of maize kernels with an aflatoxigenic strain. All evaluated strains significantly (p < 0.05) reduced aflatoxin contamination in maize kernels. The aflatoxin B₁ (AFB₁) reduction ranged from 6 to 60%. The strain A. flavus ARG5/30 isolated from maize kernels would be a good candidate as a potential biocontrol agent to be used in maize, since it was characterized as neither aflatoxin nor CPA producer, morphotype L, MAT 1-1 idiomorph, and reduced AFB₁ content in maize kernels by 59%. This study showed the competitive ability of potential aflatoxin biocontrol agents to be evaluated under field trials in a maize agro-ecosystem in Argentina.

Prevalence of Aflatoxin Contamination in Maize and Groundnut in Ghana: Population Structure, Distribution, and Toxigenicity of the Causal Agents

Aflatoxin contamination in maize and groundnut is perennial in Ghana with substantial health and economic burden on the population. The present study examined for the first time the prevalence of aflatoxin contamination in maize and groundnut in major producing regions across three agroecological zones (AEZs) in Ghana. Furthermore, the distribution and aflatoxin-producing potential of Aspergillus species associated with both crops were studied. Out of 509 samples (326 of maize and 183 of groundnut), 35% had detectable levels of aflatoxins. Over 15% of maize and 11% of groundnut samples exceeded the aflatoxin threshold limits set by the Ghana Standards Authority of 15 and 20 ppb, respectively. Mycoflora analyses revealed various species and morphotypes within the Aspergillus section Flavi. A total of 5,083 isolates were recovered from both crops. The L morphotype of Aspergillus flavus dominated communities with 93.3% of the population, followed by Aspergillus spp. with S morphotype (6%), A. tamarii (0.4%), and A. parasiticus (0.3%). Within the L morphotype, the proportion of toxigenic members was significantly (P < 0.05) higher than that of atoxigenic members across AEZs. Observed and potential aflatoxin concentrations indicate that on-field aflatoxin management strategies need to be implemented throughout Ghana. The recovered atoxigenic L morphotype fungi are genetic resources that can be employed as biocontrol agents to limit aflatoxin contamination of maize and groundnut in Ghana. Copyright © 2018 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Frequent Shifts in Aspergillus flavus Populations Associated with Maize Production in Sonora, Mexico

Aspergillus flavus frequently contaminates maize, a critical staple for billions of people, with aflatoxins. Diversity among A. flavus L morphotype populations associated with maize in Sonora, Mexico was assessed and, in total, 869 isolates from 83 fields were placed into 136 vegetative compatibility groups (VCGs) using nitrate-nonutilizing mutants. VCG diversity indices did not differ in four agroecosystems (AES) but diversity significantly differed among years. Frequencies of certain VCGs changed manyfold over single years in both multiple fields and multiple AES. Certain VCGs were highly frequent (>1%) in 2006 but frequencies declined repeatedly in each of the two subsequent years. Other VCGs that had low frequencies in 2006 increased in 2007 and subsequently declined. None of the VCGs were consistently associated with any AES. Fourteen VCGs were considered dominant in at least a single year. However, frequencies often varied significantly among years. Only 9% of VCGs were detected all 3 years whereas 66% were detected in only 1 year. Results suggest that the most realistic measurements of both genetic diversity and the frequency of A. flavus VCGs are obtained by sampling multiple locations in multiple years. Single-season sampling in many locations should not be substituted for sampling over multiple years.

Aspergillus section Flavi community structure in Zambia influences aflatoxin contamination of maize and groundnut

Aflatoxins are cancer-causing, immuno-suppressive mycotoxins that frequently contaminate important staples in Zambia including maize and groundnut. Several species within Aspergillus section Flavi have been implicated as causal agents of aflatoxin contamination in Africa. However, Aspergillus populations associated with aflatoxin contamination in Zambia have not been adequately detailed. Most of Zambia's arable land is non-cultivated and Aspergillus communities in crops may originate in non-cultivated soil. However, relationships between Aspergillus populations on crops and those resident in non-cultivated soils have not been explored. Because characterization of similar fungal populations outside of Zambia have resulted in strategies to prevent aflatoxins, the current study sought to improve understanding of fungal communities in cultivated and non-cultivated soils and in crops. Crops (n=412) and soils from cultivated (n=160) and non-cultivated land (n=60) were assayed for Aspergillus section Flavi from 2012 to 2016. The L-strain morphotype of Aspergillus flavus and A. parasiticus were dominant on maize and groundnut (60% and 42% of Aspergillus section Flavi, respectively). Incidences of A. flavus L-morphotype were negatively correlated with aflatoxin in groundnut (log y=2.4990935-0.09966x, R2=0.79, P=0.001) but not in maize. Incidences of A. parasiticus partially explained groundnut aflatoxin concentrations in all agroecologies and maize aflatoxin in agroecology III (log y=0.1956034+0.510379x, R2=0.57, P<0.001) supporting A. parasiticus as the dominant etiologic agent of aflatoxin contamination in Zambia. Communities in both non-cultivated and cultivated soils were dominated by A. parasiticus (69% and 58%, respectively). Aspergillus parasiticus from cultivated and non-cultivated land produced statistically similar concentrations of aflatoxins. Aflatoxin-producers causing contamination of crops in Zambia may be native and, originate from non-cultivated areas, and not be introduced with non-native crops such as maize and groundnut. Non-cultivated land may be an important reservoir from which aflatoxin-producers are repeatedly introduced to cultivated areas. The potential of atoxigenic members of the A. flavus-L morphotype for management of aflatoxin in Zambia is also suggested. Characterization of the causal agents of aflatoxin contamination in agroecologies across Zambia gives support for modifying fungal community structure to reduce the aflatoxin-producing potential.

A Survey of Aflatoxin-Producing Aspergillus sp. from Peanut Field Soils in Four Agroecological Zones of China

Peanut pods are easily infected by aflatoxin-producing Aspergillus sp.ecies from field soil. To assess the aflatoxin-producing Aspergillus sp. in different peanut field soils, 344 aflatoxin-producing Aspergillus strains were isolated from 600 soil samples of four agroecological zones in China (the Southeast coastal zone (SEC), the Yangtze River zone (YZR), the Yellow River zone (YR) and the Northeast zone (NE)). Nearly 94.2% (324/344) of strains were A. flavus and 5.8% (20/344) of strains were A. parasiticus. YZR had the highest population density of Aspergillus sp. and positive rate of aflatoxin production in isolated strains (1039.3 cfu·g-1, 80.7%), the second was SEC (191.5 cfu·g-1, 48.7%), the third was YR (26.5 cfu·g-1, 22.7%), and the last was NE (2.4 cfu·g-1, 6.6%). The highest risk of AFB₁ contamination on peanut was in YZR which had the largest number of AFB₁ producing isolates in 1g soil, followed by SEC and YR, and the lowest was NE. The potential risk of AFB₁ contamination in peanuts can increase with increasing population density and a positive rate of aflatoxin-producing Aspergillus sp. in field soils, suggesting that reducing aflatoxigenic Aspergillus sp. in field soils could prevent AFB₁ contamination in peanuts.

Degeneration of aflatoxin gene clusters in Aspergillus flavus from Africa and North America

Aspergillus flavus is the most common causal agent of aflatoxin contamination of food and feed. However, aflatoxin-producing potential varies widely among A. flavus genotypes with many producing no aflatoxins. Some non-aflatoxigenic genotypes are used as biocontrol agents to prevent contamination. Aflatoxin biosynthesis genes are tightly clustered in a highly conserved order. Gene deletions and presence of single nucleotide polymorphisms (SNPs) in aflatoxin biosynthesis genes are often associated with A. flavus inability to produce aflatoxins. In order to identify mechanisms of non-aflatoxigenicity in non-aflatoxigenic genotypes of value in aflatoxin biocontrol, complete cluster sequences of 35 A. flavus genotypes from Africa and North America were analyzed. Inability of some genotypes to produce aflatoxin resulted from deletion of biosynthesis genes. In other genotypes, non-aflatoxigenicity originated from SNP formation. The process of degeneration differed across the gene cluster; genes involved in early biosynthesis stages were more likely to be deleted while genes involved in later stages displayed high frequencies of SNPs. Comparative analyses of aflatoxin gene clusters provides insight into the diversity of mechanisms of non-aflatoxigenicity in A. flavus genotypes used as biological control agents. The sequences provide resources for both diagnosis of non-aflatoxigenicity and monitoring of biocontrol genotypes during biopesticide manufacture and in the environment.

Leaf application of a sprayable bioplastic-based formulation of biocontrol Aspergillus flavus strains for reduction of aflatoxins in corn

BACKGROUND

Applying non-aflatoxin-producing Aspergillus flavus isolates to the soil has been shown to be effective in reducing aflatoxin levels in harvested crops, including peanuts, cotton and corn. The aim of this study was to evaluate the possibility of controlling aflatoxin contamination using a novel sprayable formulation consisting of a partially gelatinized starch-based bioplastic dispersion embedded with spores of biocontrol A. flavus strains, which is applied to the leaf surfaces of corn plants.

RESULTS

The formulation was shown to be adherent, resulting in colonization of leaf surfaces with the biocontrol strain of A. flavus, and to reduce aflatoxin contamination of harvested kernels by up to 80% in Northern Italy and by up to 89% in the Mississippi Delta. The percentage of aflatoxin-producing isolates in the soil reservoir under leaf-treated corn was not significantly changed, even when the soil was amended with additional A. flavus as a model of changes to the soil reservoir that occur in no-till agriculture.

CONCLUSIONS

This study indicated that it is not necessary to treat the soil reservoir in order to achieve effective biocontrol of aflatoxin contamination in kernel corn. Spraying this novel bioplastic-based formulation to leaves can be an effective alternative in the biocontrol of A. flavus in corn. © 2015 Society of Chemical Industry.

Simultaneous decontamination and drying of rough rice using combined pulsed light and holding treatment

BACKGROUND

Pulsed light (PL) technology has been proven effective in food disinfection. However, increasing the light intensity or treatment time could swiftly increase the temperature of the food product. Using the thermal effect in an appropriate way may achieve a simultaneous disinfection and drying effect. The objective of this study was to investigate the feasibility of simultaneous disinfection and drying of rough rice using PL and holding treatment.

RESULTS

Freshly harvested rice samples were inoculated by Aspergillus flavus (A. flavus) and treated using PL under different intensities and durations followed by holding treatment. The PL treatment under intensity of 1.08 W cm(-2) for 21 s led to a reduction of 0.29 log cfu g(-1) on the population size of A. flavus spores. After holding treatment, a 5.2 log cfu g(-1) reduction was achieved. The corresponding total moisture removal reached 3.3% points. No adverse effect on milling quality was detected after the treatment.

CONCLUSION

The obtained results revealed that the combined PL and holding treatment had good potential for successful application in the rice industry to simultaneously achieve disinfection and drying. © 2015 Society of Chemical Industry.

Non-aflatoxigenic Aspergillus flavus as potential biocontrol agents to reduce aflatoxin contamination in peanuts harvested in Northern Argentina

Biological control is one of the most promising strategies for preventing aflatoxin contamination in peanuts at field stage. A population of 46 native Aspergillus flavus nonaflatoxin producers were analysed based on phenotypic, physiological and genetic characteristics. Thirty-three isolates were characterized as L strain morphotype, 3 isolates as S strain morphotype, and 10 isolates did not produce sclerotia. Only 11 of 46 non-aflatoxigenic isolates did not produce cyclopiazonic acid. The vegetative compatibility group (VCG) diversity index for the population was 0.37. For field trials we selected the non-aflatoxigenic A. flavus AR27, AR100G and AFCHG2 strains. The efficacy of single and mixed inocula as potential biocontrol agents in Northern Argentina was evaluated through a 2-year study (2014-2015). During the 2014 peanut growing season, most of the treatments reduced the incidence of aflatoxigenic strains in both soil and peanut kernel samples, and no aflatoxin was detected in kernels. During the 2015 growing season, there was a reduction of aflatoxigenic strains in kernel samples from the plots treated with the potential biocontrol agents. Reductions of aflatoxin contamination between 78.36% and 89.55% were observed in treated plots in comparison with the un-inoculated control plots. This study provides the first data on aflatoxin biocontrol based on competitive exclusion in the peanut growing region of Northern Argentina, and proposes bioproducts with potential use as biocontrol agents.

Environmental Factors Related to Fungal Wound Contamination after Combat Trauma in Afghanistan, 2009-2011

Environmental characteristics, along with known risk factors, may help predict likelihood of mold contamination after injury.

During the recent war in Afghanistan (2001–2014), invasive fungal wound infections (IFIs) among US combat casualties were associated with risk factors related to the mechanism and pattern of injury. Although previous studies recognized that IFI patients primarily sustained injuries in southern Afghanistan, environmental data were not examined. We compared environmental conditions of this region with those of an area in eastern Afghanistan that was not associated with observed IFIs after injury. A larger proportion of personnel injured in the south (61%) grew mold from wound cultures than those injured in the east (20%). In a multivariable analysis, the southern location, characterized by lower elevation, warmer temperatures, and greater isothermality, was independently associated with mold contamination of wounds. These environmental characteristics, along with known risk factors related to injury characteristics, may be useful in modeling the risk for IFIs after traumatic injury in other regions.