Aflatoxins are potent Aspergillus mycotoxins that contaminate food and feed, thereby impacting health and trade. Biopesticides with atoxigenic A. flavus as active ingredients are used to reduce aflatoxin contamination in crops. The mechanism of aflatoxin biocontrol is primarily attributed to competitive exclusion but sometimes aflatoxin is reduced by greater amounts than can be explained by displacement of aflatoxin-producing fungi on the crop. Objectives of this study were to 1) evaluate the ability of atoxigenic A. flavus genotypes to degrade aflatoxin B1 (AFB1) and 2) characterize impacts of temperature, time, and nutrient availability on AFB1 degradation by atoxigenic A. flavus. Aflatoxin-contaminated maize was inoculated with atoxigenic isolates in three separate experiments that included different atoxigenic genotypes, temperature, and time as variables. Atoxigenic genotypes varied in aflatoxin degradation, but all degraded AFB1 > 44% after seven days at 30°C. The optimum temperature for AFB1 degradation was 25-30°C which is similar to the optimum range for AFB1 production. In a time-course experiment, atoxigenics degraded 40% of AFB1 within three days, and 80% of aflatoxin was degraded by day 21. Atoxigenic isolates were able to degrade and utilize AFB1 as a sole carbon source in a chemically defined medium, but quantities of AFB1 degraded declined as glucose concentrations increased. Degradation may be an additional mechanism through which atoxigenic A. flavus biocontrol products reduce aflatoxin contamination pre- and/or post-harvest. Thus, selection of optimal atoxigenic active ingredients can include assessment of both competitive ability in agricultural fields and their ability to degrade aflatoxins.

Fungi can synthesize a broad array of secondary metabolite chemicals. The genes underpinning their biosynthesis are typically arranged in tightly linked clusters in the genome. For example, ∼25 genes responsible for the biosynthesis of carcinogenic aflatoxins by Aspergillus section Flavi species are grouped in a ∼70 Kb cluster. Assembly fragmentation prevents assessment of the role of structural genomic variation in secondary metabolite evolution in this clade. More comprehensive analyses of secondary metabolite evolution will be possible by working with more complete and accurate genomes of taxonomically diverse Aspergillus species. Here, we combined short and long read DNA sequencing to generate a highly contiguous genome of the aflatoxigenic fungus, Aspergillus pseudotamarii (isolate NRRL 25517 = CBS 766.97; scaffold N50 = 5.5 Mb). The nuclear genome is 39.4 Mb, encompassing 12,639 putative protein-encoding genes and 74-97 candidate secondary metabolite biosynthesis gene clusters. The circular mitogenome is 29.7 Kb and contains 14 protein-encoding genes that are highly conserved across the genus. This highly contiguous A. pseudotamarii genome assembly enables comparisons of genomic rearrangements between Aspergillus section Flavi series Kitamyces and series Flavi. Although the aflatoxin biosynthesis gene cluster of A. pseudotamarii is conserved with Aspergillus flavus, the cluster has an inverted orientation relative to the telomere and occurs on a different chromosome.

Tomato is among the most cultivated vegetable crops worldwide, and bacterial wilt (BW) caused by the Ralstonia solanacearum species complex (RSSC) is the most devastating disease affecting tomato, impacting food and nutrition security in many areas. Pesticides used for controlling plant diseases are hazardous to producers, consumers, and the environment, whereas biological control is potentially a sustainable and environmentally safe alternative for disease management. To identify efficient biocontrol agents (BCAs), twenty-five potential BCA isolates were screened for control efficacy to BW on ten-day-old tomato seedlings of highly susceptible (L390) and moderately resistant (L180) cultivars previously inoculated with R. solanacearum strain PSS4 (=Asian origin, Race 1, Phylotype I; Biovar 3). After ten days incubation at 28 °C in the growth chamber, wilting (W%) and biocontrol efficacy (BE%) percent were evaluated. Of the 25 BCAs tested, four significantly reduced W%, with BE% ranging from 50% to 80% for both varieties. The four BCA isolates were identified as Talaromyces sp., Trichoderma sp., Bacillus sp., and Variovorax sp. The seedling method allows the rapid and cost-effective in vivo screening of many potential BCAs to reliably identify those with higher bacterial wilt control efficacy for further testing.