Location: Pest Management and Biocontrol Research
2023 Annual Report
Accomplishments
1. Identification of potential biocontrol isolates for mitigation of aflatoxin contamination in chilies. Dried red chili is frequently contaminated with aflatoxins. Although aflatoxin biocontrol products have been developed specifically for mitigation of aflatoxin contamination in oil seed crops, biocontrol strains with superior ability to reduce aflatoxin contamination in chilies have not been previously identified. Non-aflatoxigenic Aspergillus flavus genotypes associated with chilies collected in Nigeria were isolated and characterized by ARS researchers in Maricopa, Arizona, and in laboratory tests they reduced aflatoxins in chilies significantly more than biocontrol strains that are active ingredients in currently registered biocontrol products. These isolates are a potential resource for developing new biocontrol products specifically for control of aflatoxins in red chilies.
2. An analysis of natural Aspergillus flavus populations from Greece, Spain, and Serbia is a close relative of a registered biocontrol product present across southern Europe. To date, there is one aflatoxin biocontrol product in Europe, AF-X1, and it is currently registered for use only in Italy. Aspergillus flavus populations were examined on corn from Spain, Greece, and Serbia, all countries with an aflatoxin problem, to determine whether use of AF-X1 would require the introduction of novel genetic types. Using simple sequence repeat (SSR) markers, ARS researchers in Maricopa, Arizona, discovered that close relatives of AF-X1 were found in all three countries, suggesting that AF-X1 can be safely and effectively used throughout southern Europe where aflatoxin mitigation is needed.
3. Characterization of crop host influences on competition between species of aflatoxin-producing fungi. Maize and groundnuts, two crop hosts that differ in nutrient composition and physiology, are staple crops that are highly susceptible to aflatoxin contamination. Aflatoxins are produced by several Aspergillus species that co-occur and compete on crops. Results of a series of co-inoculation experiments on maize and groundnut kernels by ARS researchers in Maricopa, Arizona, indicated that complex interactions between crop hosts and different Aspergillus species modulate Aspergillus community structure and subsequent aflatoxin contamination. Understanding factors that impact sporulation, dispersal, crop infection, and aflatoxin production by different Aspergillus species is critical for developing crop management practices that will minimize aflatoxin contamination.
4. A new chromosome-level genome assembly of Aspergillus pseudotamarii reveals extensive genomic rearrangements relative to A. flavus. Aspergillus pseudotamarii is an understudied aflatoxin-producing fungus related to A. flavus. A highly contiguous genome of this species was generated by ARS researchers in Maricopa, Arizona, using a combination of short read and long read sequencing technologies. This contiguous genome showed numerous large-scale genomic rearrangements relative to A. flavus, including the region containing the aflatoxin biosynthesis cluster. Better quality genomes of Aspergillus species will be useful for developing genetic screens to identify opportunistic pathogens in crops and stored food products and for understanding the molecular evolution of secondary metabolite biosynthesis gene clusters in molds.
Review Publications
Garcia-Gonzalez, J., Mehl, H.L., Langston, D.B., Rideout, S.L. 2022. Planting date and cultivar selection to manage southern blight in potatoes in the mid-Atlantic United States. Crop Protection. 162. Article 106077. https://doi.org/10.1016/j.cropro.2022.106077.
Kaur, N., Mehl, H.L. 2022. Distribution of G143A mutations conferring fungicide resistance in Virginia populations of Parastagonospora nodorum infecting wheat. Plant Health Progress. 23(1):28-32. https://doi.org/10.1094/PHP-05-21-0082-RS.
Singh, P., Mehl, H.L., Orbach, M.J., Callicott, K.A., Cotty, P.J. 2022. Genetic diversity of Aspergillus flavus associated with chili in Nigeria and identification of haplotypes with potential in aflatoxin mitigation. Plant Disease. 106(7):1818-1825. https://doi.org/10.1094/PDIS-07-21-1464-RE.
Weaver, M.A., Callicott, K.A., Mehl, H.L., Opoku, J., Park, L.C., Fields, K., Mandel, J.R. 2022. Characterization of the Aspergillus flavus population from highly aflatoxin-contaminated corn in the United States. Toxins. 14(11). Article 755. https://doi.org/10.3390/toxins14110755.
Hagler, J.R., Casey, M.T., Hull, J.J., Machtley, S.A. 2022. A labor-saving marking and sampling technique for mark-release-recapture research. Entomologia Experimentalis et Applicata. 171(2):138-145. https://doi.org/10.1111/eea.13259.
Brent, C.S., Heu, C., Gross, R.J., Fan, B., Langhorst, D.R., Hull, J.J. 2022. RNAi-mediated manipulation of cuticle coloration genes in Lygus hesperus Knight (Hemiptera: Miridae). Insects. 13(11). Article 986. https://doi.org/10.3390/insects13110986.
