Atoxigenic Strains Research Articles

Keeping toxigenic Aspergillus section Flavi and aflatoxin contamination at bay by deploying atoxigenic-based biocontrol products during production of groundnut and maize in Mozambique.

Aflatoxins, produced by aflatoxigenic Aspergillus section Flavi fungi, commonly occur in groundnut and maize grown in Mozambique and have long been associated with high prevalence of liver cancer, stunting, and restricted access to lucrative international markets. Effective aflatoxin control options in the country are limited and not adequately explored. Biocontrol products based on atoxigenic strains of A. flavus provide viable aflatoxin mitigation measures but require development for Mozambique. Four hundred and sixty-eight (468) and 558 groundnut and maize farmers, respectively, voluntarily evaluated the effectiveness of two biocontrol products (Aflasafe MWMZ01 and Aflasafe MZ02), each containing as active ingredients four distinct atoxigenic isolates of A. flavus belonging to native vegetative compatibility groups (VCGs), at preventing aflatoxin contamination and displacement of aflatoxigenic fungi for 2 years in various agro-ecologies. Most groundnut and maize treated with the biocontrol products were below maximum levels for food in the European Union (EU; 85%; p < 0.01) and the United States (US; 99%; p < 0.01). In contrast, most non-treated maize and groundnut (ranging from 38 to 70%; p = 0.05) were above the EU and US maximum allowable levels for food. Aflatoxin reductions ranged from 78 to 98% (p < 0.01) in treated groundnut, and from 61 to 93% (p < 0.01) in treated maize. Toxigenic fungi were almost completely displaced from soils and crops by the applied atoxigenic active ingredients. This study revealed that the atoxigenic based biocontrol technology is effective in Mozambique at displacing aflatoxigenic fungi and reducing aflatoxin accumulation in both groundnut and maize but a combination with other management tools is encouraged for better retention of crop quality along the value chain.

Application and antagonistic mechanisms of atoxigenic Aspergillus strains for the management of fungal plant diseases.

This review covers, for the first time, all methods based on the use of Aspergillus strains as biocontrol agents for the management of plant diseases caused by fungi and oomycetes. Atoxigenic Aspergillus strains have been screened in a variety of hosts, such as peanuts, maize kernels, and legumes, during the preharvest and postharvest stages. These strains have been screened against a wide range of pathogens, such as Fusarium, Phytophthora, and Pythium species, suggesting a broad applicability spectrum. The highest efficacies were generally observed when using non-toxigenic Aspergillus strains for the management of mycotoxin-producing Aspergillus strains. The modes of action included the synthesis of antifungal metabolites, such as kojic acid and volatile organic compounds (VOCs), secretion of hydrolytic enzymes, competition for space and nutrients, and induction of disease resistance. Aspergillus strains degraded Sclerotinia sclerotiorum sclerotia, showing high control efficacy against this pathogen. Collectively, although two Aspergillus strains have been commercialized for aflatoxin degradation, a new application of Aspergillus strains is emerging and needs to be optimized.

Technologies to decontaminate aflatoxins in foods: a review

SummaryAflatoxins are toxic secondary metabolites produced by Aspergillus spp., found in staple food commodities. Aflatoxins are carcinogenic, teratogenic, and mutagenic and pose a serious threat to the health of humans. The identification and quantification of aflatoxins in foods is a major challenge to guarantee food safety. Therefore, developing feasible, sensitive, and robust methods for decontamination is paramount, with short processing time and negligible impact on quality. This review evaluates recent novel technologies for aflatoxins decontamination by physical methods (microwave heating, Gama and electron beam irradiation, pulse light and ultraviolet), chemical methods (ozone, natural plant extracts, and organic acids), and biological methods (atoxigenic Aspergillus strains, Trichoderma spp., and bacteria and yeast). The study highlights on the cutting‐edge technologies of smart packaging and artificial intelligence (AI). To achieve more efficiency and adaptability to different food matrices in aflatoxins decontamination, the study suggests integrating multiple strategies. The study also recommends integrating Partnership for Delivery (P4D) to share the responsibility to increase the chance for success and control aflatoxins in foods.

Sporulation and Dispersal of the Biological Control Agent Aspergillus flavus AF36 Under Field Conditions.

Aflatoxins are carcinogens produced by the fungi Aspergillus flavus and A. parasiticus that contaminate pistachio crops. International markets reject pistachio when aflatoxins exceed permitted maximum levels. Releasing the atoxigenic strain AF36 of A. flavus is the leading aflatoxin pre-harvest control method. The product AF36 Prevail, sorghum grains coated with AF36 propagules, has been used in California since 2017. However, a high percentage of grains of the Prevail fail to sporulate in orchards. Here, the effect of soil moisture on the percentage of AF36 product grains sporulating (SG) and the quantity of spores per grain using a sporulation index (SI) was determined. Under controlled conditions, SG was higher than 85% when soil moisture was 13% or more, and SI increased with increasing soil moisture from 8.4 to 21%. The highest AF36 sporulation occurred near the micro-sprinklers when the grains were not impacted by the irrigation water drops. Arthropod predation was responsible for lost product grains, which was more pronounced in non-tilled soil than in tilled soil. Dispersal of the AF36 spores decreased markedly with the height and distance from the inoculum source, following a pattern of diffusion equations. However, AF36 spores easily reached canopies of pistachios located 10 m from the inoculum source. Our results indicate that AF36 Prevail should be applied close to the irrigation line in the moist soil area but avoiding the areas where excess irrigation causes water accumulation. The biocontrol of aflatoxins in California's pistachio production areas was optimized by improving the field realization of the biological control agent.

Response of broilers to dietary inclusion of atoxigenic Aspergillus flavus strain as a biocontrol strategy of aflatoxin

ABSTRACT The objective of this trial was to evaluate how broilers responded to Aspergillus flavus strains that are toxigenic and atoxigenic. The study included four treatments in a 2 × 2 factorial design, with six replicates of 10 birds each. As a result of this study measuring feed intake (FI), weight gain (WG), feed conversion ratio (FCR), crude protein, ether extract, and crude fibre, the interaction was insignificant between the toxigenic and atoxigenic diets (P > 0.05). Consumption of toxigenic aflatoxin B1-500 ppb diet decreased FI and WG but increased FCR, and cost to produce live broiler weight (P < 0.05) compared to the control diets. The addition of atoxigenic strains to contaminated diets significantly offset (P < 0.05) the effects. Diets with or without 500 ppb toxigenic and atoxigenic A. flavus did not affect the relative weight g/100gBW of pancreas, gizzard and bursa of Fabricius. Dietary inclusion of 500 ppb toxigenic Aspergillus spp. increased the relative weight (P < 0.05) of the kidney, liver, spleen and thymus while atoxigenic dietary addition reduced the relative weight of the same organs (P < 0.05). Dietary inclusion of toxigenic and atoxigenic Aspergillus spp. did not significantly affect the haematological parameters measured (P < 0.05). Dietary inclusion of 500 ppb toxigenic Aspergillus elevated the urea, creatine, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) in the serum of the broilers (P < 0.05). A decrease was observed when atox igenic A. flavus was used in the intervention for urea, creatinine and AST (P < 0.05), whereas an insignificant reduction was observed for ALT and ALP (P ≤ 0.05). This study concluded that dietary atoxigenic strain improved broiler performance, digestibility, and blood parameters.

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.

Preventive efficacy of preparations of vesicles of external membranes of atoxygenic strains of &lt;i&gt;Vibrio cholerae О1&lt;/i&gt; serogroup

Purpose: To evaluate the effectiveness and expediency of using vesicles of the outer membranes of atoxygenic strains of Vibrio cholerae O1 serogroup for the prevention of experimental cholera. Materials and methods: atoxigenic strains of V. cholerae O1 El Tor 18950 (ctxAB-tcpA-) and 18780 (ctxAB-tcpA+) isolated from the water of surface reservoirs were used to obtain vesicles. The protective properties of the obtained drugs were evaluated using a model of generalized cholera in white mice and a model of an isolated loop of the small intestine of an adult rabbit. Results: it has been shown that vesicles of the outer membranes isolated from atoxygenic strains of V. cholerae have a protective effect and prevent the development of infection in experimental animals when infected with a virulent strain of cholera. The obtained drugs are most effective when administered parenterally twice, with an interval of seven days, preventing the death of all white mice taken in the experiment and the development of pathogenetic processes in the small intestine of adult rabbits. Summary: the data obtained indicates the formation of pronounced immune protection against the disease in animals, as well as the possibility of using these structures to create preventive anti-cholera drugs.

Aflatoxigenic Aspergillus Modulates Aflatoxin-B1 Levels through an Antioxidative Mechanism.

Aflatoxins (AFs) are considered to play important functions in species of Aspergillus section Flavi including an antioxidative role, as a deterrent against fungivorous insects, and in antibiosis. Atoxigenic Flavi are known to degrade AF-B1 (B1). To better understand the purpose of AF degradation, we investigated the degradation of B1 and AF-G1 (G1) in an antioxidative role in Flavi. Atoxigenic and toxigenic Flavi were treated with artificial B1 and G1 with or without the antioxidant selenium (Se), which is expected to affect levels of AF. After incubations, AF levels were measured by HPLC. To estimate which population would likely be favoured between toxigenic and atoxigenic Flavi under Se, we investigated the fitness, by spore count, of the Flavi as a result of exposure to 0, 0.40, and 0.86 µg/g Se in 3%-sucrose cornmeal agar (3gCMA). Results showed that levels B1 in medium without Se were reduced in all isolates, while G1 did not significantly change. When the medium was treated with Se, toxigenic Flavi significantly digested less B1, while levels of G1 significantly increased. Se did not affect the digestion of B1 in atoxigenic Flavi, and also did not alter levels of G1. Furthermore, atoxigenic strains were significantly fitter than toxigenic strains at Se 0.86 µg/g 3gCMA. Findings show that while atoxigenic Flavi degraded B1, toxigenic Flavi modulated its levels through an antioxidative mechanism to levels less than they produced. Furthermore, B1 was preferred in the antioxidative role compared to G1 in the toxigenic isolates. The higher fitness of atoxigenic over toxigenic counterparts at a plant non-lethal dose of 0.86 µg/g would be a useful attribute for integration in the broader biocontrol prospects of toxigenic Flavi.

Pistachio Male Inflorescences as an Alternative Substrate for the Application of Atoxigenic Strains of Aspergillus flavus.

Aflatoxins are carcinogens mainly produced by Aspergillus flavus and A. parasiticus in susceptible crops, including pistachio. The primary inoculum sources of these pathogens are plant debris in the orchard soils. In Californian fields, one approach to controlling aflatoxin contamination is based on releasing the atoxigenic strain of A. flavus AF36 in inoculated (coated) sorghum grains (AF36 Prevail). However, this control method can fail due to poor sporulation of the AF36 strain or sorghum grain losses due to predation. In 2008 and 2018, we showed that toxigenic and atoxigenic isolates of Aspergillus spp. frequently colonized fallen inflorescences of male pistachio trees. Under controlled conditions, strain AF36 profusely colonized pistachio male inflorescences when humidity was higher than 90%. However, there were significant differences between types of inflorescence (aerial > fallen). In 2016, we considerably (P = 0.015) increased the population of AF36 on the canopies of trees when fallen inflorescences were inoculated with AF36, compared with untreated trees. In 2017 and 2018, these differences were not detected (P > 0.05) due to cross-contamination of strain AF36 between seasons and neighboring plots. In any case, the density of AF36 spores on the canopy of the inflorescence-treated trees was similar (P > 0.05) to that on trees treated with the commercial product. Here, we present a new method for applying strain AF36 based on using a natural, abundant, and uniformly distributed substrate in pistachio fields, and we discuss how it can be improved. Furthermore, our results indicate that, in pistachio orchards where biocontrol practices are not conducted, eliminating this important source of toxigenic Aspergillus inoculum is recommended.

Molecular characterization of aflatoxigenic and non-aflatoxigenic Aspergillus flavus strains isolated from peanut sold in northern Togo

The contamination of agricultural products and aflatoxins synthesis can be controlled and reduced by the application of a biological control product based on atoxinogenic Aspergillus flavus strains. The purpose of this work was to select atoxinogenic Aspergillus flavus strains that can be used in the biological control of aflatoxins. Thirty-four (34) strains of Aspergillus flavus were used and the Nor-1, Ver-1, Omt-A and AflR genes involved in the aflatoxin biosynthesis pathway were sought. The growth speed and ability of atoxigenic strains to inhibit the growth of toxigenic strains were also determined. The results showed that 50% of the strains have at least one of the genes sought and the percentages of inhibition (PI) of the atoxinogenic strains varied significantly from 16.98% to 62.50% at the threshold of 5% according to the Tukey test (p-value = 0.0000136). The mycelial growth speed (VCM) of the atoxinogenic strains varied from 7.5 to 10 mm/day with an average VCM of 8.4 ± 0.05 mm/day. Strains AKA-10; AGA-8; AMAN-35; ABA-28 and AGA-46 were found to be more effective in inhibiting mycelial growth of toxigenic strains.

Detoxification of Aflatoxins in Fermented Cereal Gruel (Ogi) by Probiotic Lactic Acid Bacteria and Yeasts with Differences in Amino Acid Profiles

Toxigenic members of Aspergillus flavus contaminate cereal grains, resulting in contamination by aflatoxin, a food safety hazard that causes hepatocellular carcinoma. This study identified probiotic strains as aflatoxin detoxifiers and investigated the changes to the grain amino acid concentrations during fermentation with probiotics in the presence of either A. flavus La 3228 (an aflatoxigenic strain) or A. flavus La 3279 (an atoxigenic strain). Generally, higher concentrations (p < 0.05) of amino acids were detected in the presence of toxigenic A. flavus La 3228 compared to the atoxigenic A. flavus La 3279. Compared to the control, 13/17 amino acids had elevated (p < 0.05) concentrations in the presence of the toxigenic A. flavus compared to the control, whereas in systems with the atoxigenic A. flavus 13/17 amino acids had similar (p > 0.05) concentrations to the control. There were interspecies and intraspecies differences in specific amino acid elevations or reductions among selected LAB and yeasts, respectively. Aflatoxins B1 and B2 were detoxified by Limosilactobacillus fermentum W310 (86% and 75%, respectively), Lactiplantibacillus plantarum M26 (62% and 63%, respectively), Candida tropicalis MY115 (60% and 77%, respectively), and Candida tropicalis YY25, (60% and 31%, respectively). Probiotics were useful detoxifiers; however, the extent of decontamination was species- and strain-dependent. Higher deviations in amino acid concentrations in the presence of toxigenic La 3228 compared to atoxigenic La 3279 suggests that the detoxifiers did not act by decreasing the metabolic activity of the toxigenic strain.

Identification of naturally occurring atoxigenic strains of Fusarium verticillioides and their potential as biocontrol agents of mycotoxins and ear rot pathogens of maize

Pre-harvest infection of seed with either of two major ear rot pathogens of maize, Fusarium verticillioides and Aspergillus flavus, leads to high economic losses and detrimental health effects to humans and animals through the production of mycotoxins, fumonisin and aflatoxin, respectively. These carcinogenic compounds are some of the most agriculturally important mycotoxins, consumption of which can lead to various cancers and stunted growth. While atoxigenic strains of A. flavus are used for biocontrol of aflatoxin, no similar biocontrol agent exists for F. verticillioides. We hypothesized that fumonisin non-producing (atoxigenic) F. verticillioides may competitively exclude or antagonize A. flavus and promote plant growth. We screened 150 isolates of Fusarium spp. collected from maize across Texas and identified several F. verticillioides isolates that did not produce fumonisin either in vitro or when grown on maize kernels. Atoxigenic strains of F. verticillioides, 302-A6 and PAL 401, variably affected plant growth following seed coating or soil injection. When pre-applied in a kernel bioassay, both strains significantly inhibited aflatoxin contamination compared to kernels later inoculated only with A. flavus. Applied as a seed coating, neither isolate inhibited aflatoxin or fumonisin accumulation in mature plants. Results confirmed that fumonisin is not required for virulence in Fusarium stalk rot infections. Application of F. verticillioides 302-A6 to developing ears reduced fumonisin accumulation by naturally-occurring toxigenic strains of F. verticillioides. This atoxigenic strain of F. verticillioides and others need to be further investigated to prove their efficacy and potential use as atoxigenic biocontrol agents to reduce fumonisin risk in corn.

Pre-harvest strategy for reducing aflatoxin accumulation during storage of maize in Argentina

Maize (Zea mays L.) is an important crop in Argentina. Aspergillus flavus may infect this crop at growing stage and the harvested kernels can be contaminated with aflatoxins (AFs), whose levels may increase during storage. In Argentina, silo bags, a hermetic type of storage system, are widely used. Biocontrol based on competitive exclusion by atoxigenic A. flavus strains is a useful tool for AFs management at pre-harvest stage. The aim of the present study was to evaluate the effect of pre-harvest biocontrol treatments on aflatoxin B1 (AFB1) accumulation in maize stored in silo bags during 3 and 6 months. Three bioformulations based on A. flavus AFCHG2 and ARG5/30 strains were applied during field trials as single and mixed inocula. Harvested kernels were stored in non-hermetic and hermetic silo bags. At initial time (t0), 3 and 6 months (t3 and t6) the following parameters were evaluated: percentage of damaged kernels, moisture content, water activity, Aspergillus section Flavi incidence, relative humidity, O2 and CO2 levels into the silo bags, and AFB1 levels. The biocontrol strains included in the 3 bioformulations were able to infect maize kernels during the field trial and displaced native toxigenic isolates. At t0 control plots showed 10.9 ± 0.4 μg/kg of AFB1 while no AFs were detected in all the treatments. Along the storage assay AFB1 levels varied from not detected (<1 μg/kg) to 20.1 ± 0.8 μg/kg. Hermetic bags were better than non-hermetic bags in preventing AFB1 accumulation. Both single and mixed inocula were effective to control AFB1 accumulation in maize kernels during 3 and 6 months. AFB1 was not detected in kernels from the treatment at field stage with AFCHG2 + ARG5/30 after 6 months of storage into hermetic bags. The application of the biocontrol agents at field stage is an appropriate tool to reduce AFB1 accumulation under storage in hermetic silo bags. This is the first report on biocontrol strategy based on native atoxigenic strains applied at pre-harvest stage to reduce AFB1 accumulation during storage in Argentina.

Discovery of the Relationship between Distribution and Aflatoxin Production Capacity of Aspergillusspecies and Soil Types in Peanut Planting Areas.

In order to study the relationship between the distribution and aflatoxin production capacity of Aspergillus species and soil types, 35 soil samples were collected from the main peanut planting areas in Xiangyang, which has 19.7 thousand square kilometers and is located in a special area with different soil types. The soil types of peanut planting areas in Xiangyang are mainly sandy loam and clay loam, and most of the soil is acidic, providing unique nature conditions for this study. The results showed that the Aspergillus sp. population in clay loam (9050 cfu/g) was significantly larger than that in sandy loam (3080 cfu/g). The percentage of atoxigenic Aspergillus strains isolated from sandy loam samples was higher than that from clay loam samples, reaching 58.5%. Meanwhile the proportion of high toxin-producing strains from clay loam (39.7%) was much higher than that from sandy loam (7.3%). Under suitable culture conditions, the average aflatoxin production capacity of Aspergillus isolates from clay loam samples (236.97 μg/L) was higher than that of strains from sandy loam samples (80.01 μg/L). The results inferred that under the same regional climate conditions, the density and aflatoxin production capacity of Aspergillus sp. in clay loam soil were significantly higher than that in sandy loam soil. Therefore, peanuts from these planting areas are at a relatively higher risk of contamination by Aspergillus sp. and aflatoxins.

The Analysis and Experimentation of Aspergillus flavus Colonizing Corn in West Tennessee

Aspergillus flavus is an opportunistic fungus that affects many crops including corn. A. flavus colonizes the ear of the corn, causing a disease known as Aspergillus ear rot (AER). AER contributes to yield loss in two ways; through fungal infection, which results in decreased kernel weight, and through contamination of the grain with aflatoxins. A. flavus has the ability to produce toxic secondary metabolites called aflatoxins which are harmful to humans and animals when consumed. Contamination with aflatoxin can result in reduced price, or rejection of grain depending on FDA regulatory limits. Due to their ability to compete with and displace toxigenic strains, atoxigenic (non‐toxin producing) strains of A. flavus have been used as a biological control, such as the Syngenta product Afla‐Guard®. The evaluation of local populations of A. flavus strains enables researchers to gather information about what is present in the field (atoxigenic or toxigenic) and can help make more informed management recommendations. Therefore, the purpose of this research was to evaluate the characteristics of an unknown isolate of A. flavus isolated from corn in West Tennessee in comparison to known atoxigenic (1 isolate from Afla‐Guard®) and toxigenic isolates (2 isolates). Each isolate was grown on barley seed and plated onto MDRB media three times (i.e. 3 replications) along with a negative control (autoclaved barley) (total of 15 plates). Radial growth and colony morphology of each isolate were evaluated at 3‐ and 5‐days after plating in a laboratory setting. Based on observations of the activity of the TN field collected isolate, it was predicted to grow slower than the Afla‐Guard®/atoxigenic isolate. Preliminary results demonstrate that the Afla‐Guard®/atoxigenic isolate did outgrow the TN strain as hypothesized. Additional research is required to determine the toxicity of the TN strain, as well as evaluation of other naturally occurring strains in TN in relation to potential use as biological controls.

Aflatoxin Contamination, Its Impact and Management Strategies: An Updated Review.

Aflatoxin, a type of mycotoxin, is mostly produced by Aspergillus flavus and Aspergillus parasiticus. It is responsible for the loss of billions of dollars to the world economy, by contaminating different crops such as cotton, groundnut, maize, and chilies, and causing immense effects on the health of humans and animals. More than eighteen different types of aflatoxins have been reported to date, and among them, aflatoxins B1, B2, G1, and G2 are the most prevalent and lethal. Early detection of fungal infection plays a key role in the control of aflatoxin contamination. Therefore, different methods, including culture, chromatographic techniques, and molecular assays, are used to determine aflatoxin contamination in crops and food products. Many countries have set a maximum limit of aflatoxin contamination (2–20 ppb) in their food and agriculture commodities for human or animal consumption, and the use of different methods to combat this menace is essential. Fungal infection mostly takes place during the pre- and post-harvest stage of crops, and most of the methods to control aflatoxin are employed for the latter phase. Studies have shown that if correct measures are adopted during the crop development phase, aflatoxin contamination can be reduced by a significant level. Currently, the use of bio-pesticides is the intervention employed in many countries, whereby atoxigenic strains competitively reduce the burden of toxigenic strains in the field, thereby helping to mitigate this problem. This updated review on aflatoxins sheds light on the sources of contamination, and the on occurrence, impact, detection techniques, and management strategies, with a special emphasis on bio-pesticides to control aflatoxins.

Validation and Ecological Niche Investigation of a New Fungal Intraspecific Competitor as a Biocontrol Agent for the Sustainable Containment of Aflatoxins on Maize Fields.

Crop yield and plant products quality are directly or indirectly affected by climate alterations. Adverse climatic conditions often promote the occurrence of different abiotic stresses, which can reduce or enhance the susceptibility to pests or pathogens. Aflatoxin producing fungi, in particular, whose diffusion and deleterious consequences on cereals commodities have been demonstrated to highly depend on the temperature and humidity conditions that threaten increasingly larger areas. Biological methods using intraspecific competitors to prevent fungal development and/or toxin production at the pre-harvest level are particularly promising, even if their efficacy could be affected by the ecological interaction within the resident microbial population. A previously characterized Aspergillus flavus atoxigenic strain was applied in two maize fields to validate its effectiveness as a biocontrol agent against aflatoxin contamination. At one month post-application, at the harvest stage, its persistence within the A. flavus population colonizing the maize kernels in the treated area was assessed, and its efficacy was compared in vitro with a representation of the isolated atoxigenic population. Results proved that our fungal competitor contained the aflatoxin level on maize grains as successfully as a traditional chemical strategy, even if representing less than 30% of the atoxigenic strains re-isolated, and achieved the best performance (in terms of bio-competitive potential) concerning endogenous atoxigenic isolates.

Control of aflatoxin using atoxigenic strains and irrigation management is complicated by maize hybrid diversity

AbstractMycotoxins produced by the fungus Aspergillus flavus are harmful to humans and animals that feed on contaminated products. This study was conducted to determine if there are any interactions between applications of an atoxigenic A. flavus, irrigation regimes, locations, and hybrids that affect contamination of maize (Zea mays L.). Total genotypic variation was 3.8% for transformed aflatoxin data, suggesting that the diverse hybrids used were a minor to moderate driver of aflatoxin variation in this experiment. Location (Loc) × year × irrigated (Irr) × genotype (Gen) for transformed aflatoxin explained 3.3% variation, which is useful in selecting reduced aflatoxin‐susceptible genotypes in differing environments. Variation from atoxigenic inoculation (Inoc) explained 2.7% variation and reduced aflatoxin accumulation by 11% on average. Location × Inoc explained 2.1% of variation, supporting the effectiveness of atoxigenic applications dependent on different locations. All effects containing Inoc × Gen totaled .45%, suggesting that genotypes could have a small influence on effectiveness of atoxigenic applications. These are critical components to understand that can aid a breeder in selecting aflatoxin‐tolerant germplasm.

Spatial and Temporal Population Dynamics of Aspergillus flavus in Commercial Pistachio Orchards in Arizona

Aspergillus flavus infects a wide range of crops, including pistachio, and subsequent aflatoxin contamination results in significant economic losses. Application of biocontrol products based on nonaflatoxigenic (atoxigenic) strains of A. flavus is one of the most effective tactics for controlling aflatoxins in crops. Both risk of aflatoxin contamination and effectiveness of biocontrol are influenced by the extent to which A. flavus spores move into pistachio tree canopies during periods of nut development. Thus, the purpose of this study was to evaluate spatial and temporal population dynamics of A. flavus, including the applied biocontrol strain AF36, in canopies of pistachio orchards in Arizona. Propagule densities of A. flavus were quantified on leaf samples collected from lower, middle, and upper canopies from spring through harvest in 2018 and 2019. A. flavus propagule densities peaked during periods of high temperature and rainfall in 2018 (up to 600 CFU/g) and 2019 (up to 23 CFU/g), which coincided with nut development and maturation. The applied biocontrol strain AF36 was detected at all canopy heights but overall propagule densities were greater in the upper and middle canopy (mean = 70 CFU/g) compared with the lower canopy (mean = 47 CFU/g). Results suggest that June to August is the period during which A. flavus inoculum increases in Arizona pistachio orchards and, to most effectively displace aflatoxin-producing fungi in tree canopies, biocontrol applications should precede this period. In addition, this study demonstrates that soil-applied biocontrol strains can successfully disperse throughout the canopies of commercial tree nut orchards.

Biodiversity and Distribution of &amp;lt;i&amp;gt;Aspergillus&amp;lt;/i&amp;gt; and Their Toxins in Maize from Western and Eastern Regions of South Africa

Aspergillus species and aflatoxins production are more prevalent during times of high heat and drought. In South Africa, there is frequent occurrence of drought as a result of climate change. The aim of this study was to investigate the biodiversity and distribution of Aspergillus species with their corresponding toxins in maize from main maize producing regions of South Africa; [Western Regions (WR) and Eastern Regions (ER)]. One hundred and twenty-three (64 from WR and 59 from ER) maize samples from the two agro-climatic regions in South Africa were analyzed using cultural, molecular and analytical methods. Across agro-climatic regions, Aspergillus species contaminated about 62% of the maize samples, while Aspergillus flavus was the most prevalent (47.15%) followed by Aspergillus fumigatus (4.69%) while the least was Aspergillus parasiticus (0.81%). The Western Regions showed a higher distribution of varieties of Aspergillus species compared to the Eastern Regions. Aflatoxins contaminated only 27.64% of the maize samples with a mean total aflatoxin concentration of 2.40 μg/kg which is below the South Africa’s set standard for total aflatoxin in food (5 μg/kg). About 10.57% of the samples produce aflatoxins above the 5 μg/kg permissible limit for total aflatoxin in foods. The ratio of toxigenic to atoxigenic strains of Aspergillus flavus was generally low in all the regions of South Africa. This study could aid policy makers to make informed decisions in developing remediation strategies for Aspergillus mycotoxins.