Resistance to fungicides in the plant pathogen Microdochium nivale

Samples of Microdochium nivale were collected from British Columbia and Ontario. The sampled isolates (161) and previously collected isolates (129) were tested for fungicide sensitivity by growing on amended media. Iprodione and propiconazole EC50 values ranged from 1 to 543 μg mL-1¬ and 0.001 to 0.87 μg mL-1 respectively. In field trials, resistance was significantly correlated with less disease. Draft genome assemblies of 13 isolates were searched for sequences associated with resistance. Alignments of the mnos-1 gene revealed a mutation (A3503G) and a deletion (Δ430-462) in iprodione-resistant isolates. Mutations in mnos-4 (G49A and C396T), and mutations in skn7 (214 SNPs, six deletions, two insertions) were associated with a subset of iprodione-resistant isolates. Mutations in the mrr1 gene (G2237A and G2392A) were associated with resistance to both fungicides in some isolates. No mutations in the propiconazole target site (cyp51) were found to be associated with propiconazole-resistant isolates of M. nivale.