Search

Pink snow mould is a serious disease on grasses and winter cereals in cold and temperate zones during winter. To better understand the basis for the variation in pathogenicity between different isolates of Microdochium nivale and M. majus and to simplify selection of highly pathogenic isolates to use when screening for resistance to pink snow mould in perennial ryegrass, we sought traits correlated with pathogenicity. Isolates of M. nivale were more pathogenic on perennial ryegrass than isolates of M. majus, as measured by survival and regrowth of perennial ryegrass after infection and incubation under simulated snow cover. Pathogenicity as measured by relative regrowth was highly correlated with fungal growth rate on potato dextrose agar (PDA) at 2°C. Measuring fungal growth on PDA therefore seems to be a relatively simple method of screening for potentially highly pathogenic isolates. In a study of a limited number of isolates, highly pathogenic isolates showed an earlier increase and a higher total specific activity of β-glucosidase, a cell wall-degrading enzyme, compared with less pathogenic isolates. None of the M. majus isolates was highly pathogenic on perennial ryegrass. Our results indicate biological differences between M. nivale and M. majus and thus strengthen the recently published sequence-based evidence for the elevation of these former varieties to species status. [ABSTRACT FROM AUTHOR]

Resistance to pink snow mould, caused by Microdochium nivale, was investigated in four resistant winter wheat lines from the USDA World Cereal Collection (CI9342, CI14106, PI173440 and PI181268) and three Nordic wheat lines (Bjørke, Rida and V1004). Pink snow mould resistance was tested in non-hardened and cold-hardened plants incubated under artificial snow cover and in detached leaf segments mounted on water agar and incubated at either 3°C in darkness or at room temperature with light during the day. The wheat lines CI9342, CI14106 and PI181268 were more resistant than the Nordic lines, both before and after cold hardening. Thus, although cold hardening strongly increases the level of snow mould resistance in all the wheat lines, some resistance mechanisms are also present prior to cold hardening in some of the resistant lines. CI9342, CI14106 and PI181268 also had a higher level of resistance than the other lines in the detached leaf assay, indicating that these lines have some resistance mechanisms acting in the leaves. The resistance of PI173440 was expressed only in intact hardened plants and not in non-hardened plants or in detached leaves. This indicates that this line relies on cold hardening-related changes in the crown for its resistance. In the detached leaf assay the rate of lesion development varied greatly between leaves of different order. The highest correlation with the whole plant test was obtained when using secondary leaves and incubation at 3°C in the dark. [ABSTRACT FROM AUTHOR]

The effects of chitosan on resistance to pink snow mould (Microdochium nivale) were studied in young winter wheat (Triticum aestivumL.) and perennial ryegrass (Lolium perenneL.) under controlled environmental conditions. In perennial ryegrass, the putative defence activator Bion was also tested. Resistance was measured as regrowth of plants after inoculation withM. nivaleand incubation in darkness at 2°C. In winter wheat, pre-treatment with chitosan at 1000 μg per plant increased resistance to subsequent infection byM. nivale, but this effect was less significant in a replicate experiment. Chitosan-treated winter wheat plants expressed the gene for the pathogenesis-related protein chitinase at higher levels than non-treated plants. Chitinase gene expression was also stimulated byM. nivaleinfection in winter wheat. Perennial ryegrass pre-treated with Bion or chitosan and inoculated withM. nivaledid not display better regrowth after incubation than non-treated, inoculated plants. Rather, regrowth was reduced in some of the Bion-treated plants after incubation. We speculate that the cost or the mechanism of induced resistance makes Bion non-effective in plants that are not actively growing. Bion at concentrations of 10, 100 and 1000 μg active ingredient per ml, and the highest concentration of chitosan used (2000 μg per ml) reducedin vitrogrowth of the pathogen, suggesting that both defence activators possess antifungal activity. [ABSTRACT FROM AUTHOR]