Core Ideas Biocontrol strains are effective at reducing AF levels in maize. Native and commercially available biocontrol strains are equally effective in reducing AF levels. Deploying strains of opposite mating types in combination can lead to the greatest reduction in AF contamination. The fungus Aspergillus flavus can contaminate maize (Zea mays L.) by producing aflatoxins (AFs), secondary metabolites that have been shown to have adverse health impacts for humans and animals when ingested in large quantities or over extended lengths of time. The FDA strictly regulates that corn contaminated with more than 20 parts per billion (ppb) AFs cannot be marketed for human consumption; therefore, AFs cost US corn growers billions of dollars every year. Current methods to curb aflatoxin contamination in fields involve dense applications of non‐aflatoxigenic biological control (biocontrol) strains, either Afla‐Guard or AF36, that outcompete native strains and reduce toxicity levels throughout the field. This fungus is heterothallic and sexual reproduction occurs between isolates of opposite mating types, either MAT1−1 or MAT1−2. Both biocontrol strains are of a single mating type MAT1−2. The implications of adding a strain of opposite mating type (MAT1−1) to this formulation are unknown. Here we examine the ability of native non‐aflatoxigenic strains applied singly and in combination to reduce AF concentrations in a cornfield in Rocky Mount, NC. We show that native, non‐aflatoxigenic A. flavus strains reduced aflatoxin levels and increased yield when compared with untreated controls. Moreover, the strain formulations that included sexually compatible MAT1−1 and MAT1−2 strains showed the greatest reduction in aflatoxin levels. We propose that using a combination of native isolates of opposite mating types reduces AF levels further than current biocontrol agents of a single mating‐type strain and could potentially provide a more long‐term form of control.
Aspergillus flavus is an agriculturally important fungus that causes ear rot of maize and produces aflatoxins, of which B1 is the most carcinogenic naturally-produced compound. In the US, the management of aflatoxins includes the deployment of biological control agents that comprise two nonaflatoxigenic A. flavus strains, either Afla-Guard (member of lineage IB) or AF36 (lineage IC). We used genotyping-by-sequencing to examine the influence of both biocontrol agents on native populations of A. flavus in cornfields in Texas, North Carolina, Arkansas, and Indiana. This study examined up to 27,529 single-nucleotide polymorphisms (SNPs) in a total of 815 A. flavus isolates, and 353 genome-wide haplotypes sampled before biocontrol application, three months after biocontrol application, and up to three years after initial application. Here, we report that the two distinct A. flavus evolutionary lineages IB and IC differ significantly in their frequency distributions across states. We provide evidence of increased unidirectional gene flow from lineage IB into IC, inferred to be due to the applied Afla-Guard biocontrol strain. Genetic exchange and recombination of biocontrol strains with native strains was detected in as little as three months after biocontrol application and up to one and three years later. There was limited inter-lineage migration in the untreated fields. These findings suggest that biocontrol products that include strains from lineage IB offer the greatest potential for sustained reductions in aflatoxin levels over several years. This knowledge has important implications for developing new biocontrol strategies.
Aspergillus flavus is an agriculturally important fungus that causes ear rot of maize and produces aflatoxins (AFs), of which B1 is the most potent carcinogen known. In the US, the management of AFs includes the deployment of biological control agents that comprise two nonaflatoxigenic A. flavus strains, either Afla-Guard (member of lineage IB) or AF36 (lineage IC). We used genotyping-by-sequencing to examine the influence of both biocontrol agents on native populations of A. flavus in cornfields in Texas, North Carolina, Arkansas, and Indiana. This study examined up to 27,529 single-nucleotide polymorphisms (SNPs) in a total of 815 A. flavus isolates, and 353 genome-wide haplotypes sampled before biocontrol application, three months after biocontrol application, and up to three years after initial application. Here, we report that the two distinct A. flavus evolutionary lineages IB and IC differ significantly in their frequency distributions across states. We provide evidence of increased unidirectional gene flow from lineage IB into IC, inferred to be due to the applied Afla-Guard biocontrol strain. Genetic exchange and recombination of biocontrol strains with native strains was detected in as little as three months after biocontrol application and up to one and three years later. There was limited inter-lineage migration in the untreated fields. These findings suggest that biocontrol products that include strains from lineage IB offer the greatest potential for sustained reductions in aflatoxin levels over several years. This knowledge has important implications for developing new biocontrol strategies.
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