Pathogenicity, host specificity and genetic diversity in Norwegian isolates of Microdochium nivale and Microdochium majus

Microdochium majusandMicrodochium nivalecause serious disease problems in grasses and cereal crops in the temperate regions. Both fungi can infect the plants during winter (causing pink snow mould) as well as under cool humid conditions during spring and fall. We conducted a pathogenicity test of 15 M. nivaleisolates and twoM. majusisolates from Norway at low temperature on four different grass cultivars ofLolium perenneandFestuloliumhybrids. Significant differences betweenM. nivaleisolates in the ability to cause pink snow mould were detected. TheM. nivalestrains originally isolated from grasses were more pathogenic than isolates from cereals. The genetic diversity ofM. nivaleandM. majusisolates was studied by sequencing four genetic regions; Elongation factor-1 alpha (EF-1α), β-tubulin, RNA polymerase II (RPB2)and the Internal Transcribed Spacer (ITS). Phylogenetic trees based on the sequences of these four genetic regions resolvedM. nivaleandM. majusisolates into separate clades. Higher genetic diversity was found amongM. nivaleisolates than amongM. majusisolates.M. nivaleisolates revealed genetic differences related to different host plants (grasses vs. cereals) and different geographic regions (Norway and UK vs. North America). Sequence results from theRPB2and β-tubulin genes were more informative than those from ITS andEF-1α. The genetic and phenotypic differences detected between NorwegianM. nivaleisolates from cereals and grasses support the assumption that host specialization exist withinM. nivaleisolates.