Induced selection of tebuconazole-resistant Aspergillus flavus isolates during germination of treated corn seeds

Authors: MORENA, CHIARA - University Of Bologna, Italy; ACCINELLI, CESARE - University Of Bologna, Italy; BRUNO, VERONICA - University Of Bologna, Italy; Abbas, Hamed; Paulk, Ryan; SHIER, WAYNE - University Of Minnesota

Submitted to: Journal of Agriculture and Food Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2024
Publication Date: 12/6/2024
Citation: Morena, C., Accinelli, C., Bruno, V., Abbas, H.K., Paulk, R.T., Shier, W.T. 2024. Induced selection of tebuconazole-resistant Aspergillus flavus isolates during germination of treated corn seeds. Journal of Agriculture and Food Research. 19(2025)101566.
DOI: https://doi.org/10.1016/j.jafr.2024.101566

Interpretive Summary: Unfettered use of antifungal azoles in agricultural applications has the potential for selecting for azole-resistant species of medically important Aspergillus fungi such as A. fumigatus and A. flavus. Identifying hotspots that induce fungal resistance to azoles is important for controlling their development. In this study, corn seeds coated with tebuconazole were evaluated for their selection of tebuconazole-resistant A. flavus isolates and their aflatoxigenicity. The abundance of aflatoxin-producing and tebuconazole-resistant isolates of A. flavus were both positively correlated with tebuconazole dosage.

Technical Abstract: Azoles are a class of antifungals widely used in human medicine and crop protection. Agricultural uses of these chemicals have raised concerns over the potential risk of selecting azole-resistant Aspergillus species, including A. fumigatus and A. flavus, and thus reducing the medical effectiveness of azoles. Azole fungicides are used for spraying crops and also in seed treatments of corn, wheat and other important agricultural crops, in which seeds are dressed with a plastic-like coat containing an azole fungicide and other seed and seedling protection agents. In this study, the effect of tebuconazole in corn seed treatment on selecting for tebuconazole-resistant A. flavus isolates was investigated. Seed-borne A. flavus isolates growing during seed germination were tested for tebuconazole resistance. When seeds were treated with increasing dosages of tebuconazole, the relative abundance of resistant isolates increased. At the recommended dosage, up to 72.1 % of the seed borne A. flavus isolates that emerged from germinating seeds were resistant to tebuconazole. Resistance increased to 83.4 and 95.1%, when dosages were doubled or tripled, respectively. Application of tebuconazole also increased the abundance of aflatoxin-producing isolates of A. flavus, from 32.2% in untreated seeds to 67.4% in seeds receiving the highest dosage. Results from this study suggest that seed treatment with tebuconazole should be included in the list of hotspots that induce resistance to azole antifungals and that measures and strategies, such as alternative fungicides with different metabolic targets, should be considered for reducing this risk.