Fungicide sensitivity of Fusarium spp. isolated from decaying potato seed tubers

Abstract

One of the most detrimental seed and storage diseases affecting potato agriculture is the fungal disease known as dry rot. This disease is caused by various species of <em>Fusarium</em>, which enter tubers through ruptures in the skin, that occur frequently during mechanized harvesting and handling, as well as during seed cutting prior to planting. Disease symptoms appear as sunken patches of darkened tissue which are often lined with mycelia and spores. <em>Fusarium</em> dry rot can cause losses in storage as well as reduced emergence when affected seed is planted. Post-harvest and seed treatment applications of chemical fungicides are the most common treatment methods, however, in the spring of 2024, Agriculture and Agri-Food Canada (AAFC) received seed tuber samples from growers in Prince Edward Island (PEI) that presented with dry rot despite having been treated with prothioconazole. Resistance to this chemical in <em>Fusarium</em> species has not yet been observed in PEI. As such, the resistance profile of the pathogen was determined by testing three isolates obtained from sample tissue (PEF 3355-2, 3355-3, and 3355-6) against eight concentrations (0, 0.01, 0.1, 1.0, 5.0, 10.0, 50.0, and 100.0 &mu;g/ml) of fungicides commonly used for dry rot management, including difenoconazole, fludioxonil, prothioconazole, and thiabendazole. DNA sequencing was also conducted which identified the species of the pathogen as <em>F. sambucinum</em>. This strain showed resistance to thiabendazole for all isolates tested (EC₅₀ of 17.82, 16.91, and 21.82 &mu;g/ml for PEF 3355-2, 3355-3, and 3355-6, respectively), but had no high level resistance to difenoconazole or prothioconazole. Resistance to fludioxonil was originally absent, but the development of mutations <em>in vitro</em> resulted in fungal sectors with resistance to this chemical in some isolates.