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Article

Context-Dependent Fitness Trade-Offs in Penicillium expansum Isolates Resistant to Multiple Postharvest Fungicides

Department of Plant Pathology, Tree Fruit Research and Extension Center, Washington State University, 1100 N. Western Ave., Wenatchee, WA 98801, USA
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Author to whom correspondence should be addressed.
Microorganisms 2025, 13(8), 1846; https://doi.org/10.3390/microorganisms13081846 (registering DOI)
Submission received: 20 June 2025 / Revised: 30 July 2025 / Accepted: 5 August 2025 / Published: 7 August 2025
(This article belongs to the Section Antimicrobial Agents and Resistance)

Abstract

Blue mold of pome fruit, caused by Penicillium expansum, is controlled through postharvest applications of thiabendazole (TBZ), pyrimethanil (PYR), and fludioxonil (FDL). However, multi-fungicide-resistant isolates have emerged in the U.S. Pacific Northwest and their impact on decay control in long-term storage is unknown. This study evaluated the fitness of P. expansum isolates sensitive to all three postharvest fungicides (wild-types) and those resistant to TBZ (single-resistant), TBZ and PYR, or PYR and FDL (dual-resistant), and triple-resistant to the three fungicides. On nutrient-poor media, resistant isolates showed reduced conidial germination, whereas no significant differences were observed in germination, mycelial growth, or sporulation between phenotypes on nutrient-rich media at 1.5 and 20 °C. Regardless of their sensitivity phenotype, FDL-resistant isolates showed increased sensitivity to osmotic and oxidative stresses. Pathogenicity and virulence were not affected by the sensitivity phenotype on apples after six months of storage at 1.5 °C. Analysis of cumulative fitness changes indicated fitness loss under low-temperature in vitro and increased fitness under fungicide selection pressure on fruit in most resistant phenotypes. Gene expression analysis showed differential regulation of fitness-related genes, with most being up-regulated by TBZ. Overall, the results suggest that resistance in P. expansum may carry context-dependent fitness penalties, especially under high-stress conditions.
Keywords: pome fruit; blue mold; fitness; gene expression; fludioxonil; pyrimethanil; thiabendazole; cumulative fitness pome fruit; blue mold; fitness; gene expression; fludioxonil; pyrimethanil; thiabendazole; cumulative fitness

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MDPI and ACS Style

Puglisi, J.T.; Amiri, A. Context-Dependent Fitness Trade-Offs in Penicillium expansum Isolates Resistant to Multiple Postharvest Fungicides. Microorganisms 2025, 13, 1846. https://doi.org/10.3390/microorganisms13081846

AMA Style

Puglisi JT, Amiri A. Context-Dependent Fitness Trade-Offs in Penicillium expansum Isolates Resistant to Multiple Postharvest Fungicides. Microorganisms. 2025; 13(8):1846. https://doi.org/10.3390/microorganisms13081846

Chicago/Turabian Style

Puglisi, Jonathan T., and Achour Amiri. 2025. "Context-Dependent Fitness Trade-Offs in Penicillium expansum Isolates Resistant to Multiple Postharvest Fungicides" Microorganisms 13, no. 8: 1846. https://doi.org/10.3390/microorganisms13081846

APA Style

Puglisi, J. T., & Amiri, A. (2025). Context-Dependent Fitness Trade-Offs in Penicillium expansum Isolates Resistant to Multiple Postharvest Fungicides. Microorganisms, 13(8), 1846. https://doi.org/10.3390/microorganisms13081846

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