Identification of mutations potentially associated with fungicide resistance in thecaphora frezii, a pathogen of peanut crops

Authors: BADARIOTTI, ESTEBAN - Catholic University Of Córdoba; Faustinelli, Paola; DIAZ, MARIA - Center Of Excellence For Products And Processes Of Córdoba (CEPROCOR); FIGUEROA, ANA - Center Of Excellence For Products And Processes Of Córdoba (CEPROCOR); ALASINO, VALERIA - Center Of Excellence For Products And Processes Of Córdoba (CEPROCOR); BELTRAMO, DANTE - Center Of Excellence For Products And Processes Of Córdoba (CEPROCOR); SORIA, NESTOR - Catholic University Of Córdoba

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2025
Publication Date: 11/7/2025
Citation: Badariotti, E.H., Faustinelli, P.C., Diaz, M.S., Figueroa, A.C., Alasino, V.R., Beltramo, D.M., Soria, N.W. 2025. Identification of mutations potentially associated with fungicide resistance in thecaphora frezii, a pathogen of peanut crops. Peanut Science. 52:1. https://doi.org/10.3146/0095-3679-52.1-PS1663.
DOI: https://doi.org/10.3146/0095-3679-52.1-PS1663

Interpretive Summary: Thecaphora frezii (T. frezii) is a fungal pathogen that causes significant losses in peanut production, especially in countries like Argentina. The primary management strategy is chemical control. However, the intensive and repeated use of fungicides has led to the emergence of resistant fungal populations. This study explores genetic variants in key T. frezii genes associated with resistance to four major fungicide classes: strobilurins (Cytochrome b), benzimidazoles (Tubulin b), carboxamides (Succinate dehydrogenase B, C, D – SDHB, SDHC, SDHD), and triazoles (CYP51). Using the T. frezii transcriptome and its reference genome from GenBank, protein sequence alignments were performed with orthologous genes from fungal species to identify potential resistance-related variants. Novel mutations were identified in genes related to carboxamides and triazoles resistance, while no variants were found in genes associated to strobilurins and benzimidazoles. These findings are important as they will enable early detection of resistant strains, optimizing fungicide use, and slowing the spread of resistance.

Technical Abstract: Thecaphora frezii (T. frezii) is the causal agent of peanut smut, a destructive disease responsible for substantial yield losses in Argentina and other peanut-producing regions. Management practices such as crop rotation, resistant cultivars, and fungicide applications have not prevented recurring outbreaks. Continuous fungicide exposure can exert selection pressure favoring resistant fungal populations.This study analyzed genetic variants in genes associated with four major fungicide classes: triazoles (CYP51), carboxamides (SDHB, SDHC, SDHD), strobilurins (CYTB), and benzimidazoles (TUBB). Protein-coding sequences from the T. frezii transcriptome and reference genome were compared with orthologous genes from related Ustilaginales species to detect amino-acid substitutions potentially related to resistance. Three conserved substitutions were identified in CYP51 (R164K, K256R, I339L) and one in SDHB (H257R), while additional non-conserved variants occurred in CYP51 (R336L), SDHB (R255A) and SDHC (A93I). No variants were observed in SDHD, CYTB, or TUBB.These results suggest that some T. frezii variants could reduce fungicide sensitivity, whereas others indicate that strobilurins and benzimidazoles may still be effective. Because the sample size was limited, our conclusions are exploratory. Nevertheless, this study provides the first genetic evidence of potential fungicide-resistance-related variants in T. frezii, emphasizing the importance of monitoring resistance evolution to ensure sustainable peanut-smut management.