Genetic diversity of Aspergillus flavus associated with chili in Nigeria and identification of haplotypes with potential in aflatoxin mitigation

Authors: SINGH, PUMMI - University Of Arizona; Mehl, Hillary; ORBACH, MARC - University Of Arizona; Callicott, Kenneth; Cotty, Peter

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2022
Publication Date: 1/27/2022
Citation: 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.
DOI: https://doi.org/10.1094/PDIS-07-21-1464-RE

Interpretive Summary: Aflatoxins are produced by the fungus Aspergillus flavus and its close relatives. In mammals, low dose exposure to aflatoxins can decrease immunity, stunt growth, and cause liver cancer. High doses can cause death. Some A. flavus isolates with a distinctive appearance (called ‘L isolates”) produce no aflatoxins (‘atoxigenic isolates’) and can be used to biologically control aflatoxins on crops as they grow by displacing toxigenic strains. The current study examined L isolates associated with chilies in Nigeria and identified atoxigenic isolates with potential for aflatoxin biological control in chilies. Genetic diversity was assessed using 17 markers. A total of 152 genetic types were detected from 325 isolates. Most of these genetic types (65%) produced B aflatoxins in laboratory tests. Atoxigenic isolates were examined for deletions in the genes necessary to make aflatoxins, and these isolates had either no deletions or one of three distinct deletion patterns. To test whether these isolates might be useful for biological control, seven atoxigenic isolates from chilies and four isolates currently used in Nigeria on corn and peanuts were individually grown on chili along with an isolate from a related species that produces high levels of aflatoxins. The atoxigenic isolates sampled from chilies reduced aflatoxins in these laboratory tests significantly more than did the isolates typically used on corn and peanuts and may represent a potential resource for developing new, targeted biological control for chilies in Nigeria.

Technical Abstract: Dried red chili (Capsicum spp.), a widely produced and consumed spice in Nigeria, is frequently contaminated by aflatoxins. Aflatoxins are potent mycotoxins of severe health and economic concern worldwide. Aspergillus flavus frequently contaminates crops with aflatoxins in warm regions; however, not all isolates are aflatoxin producers. Non-aflatoxigenic isolates have potential as biocontrol agents for aflatoxin mitigation. The current study examined the genetic diversity of A. flavus (n = 325) associated with chilies in Nigeria and identified 123 non-aflatoxigenic isolates. The Nigerian A. flavus isolates from chili were diverse at 17 microsatellite loci, with 5 to 36 alleles per locus, and included 152 haplotypes. The isolates that are active ingredients in Aflasafe, registered for aflatoxin biocontrol on maize and groundnuts in Nigeria, did not share haplotypes with the chili isolates. Of the 152 haplotypes, 65% produced aflatoxins in autoclaved maize, some of which (17%) produced more than 100,000 µg/kg of aflatoxins. Aflatoxins were not detected in 35% of the haplotypes. Cluster amplification pattern assay detected large deletion(s) in the aflatoxin biosynthetic clusters of some (32%) of the non-aflatoxigenic haplotypes. Co-infection of chili with non-aflatoxigenic isolates from chilies (n = 7) and A. aflatoxiformans resulted in a significantly greater average reduction in total aflatoxins compared to that achieved by Aflasafe active ingredient isolates (P < 0.01). These non-aflatoxigenic isolates are a genetic resource for the development of biological control products for aflatoxin mitigation in chilies in Nigeria and should be evaluated under field conditions.