Submitted to: Journal of Phytopathology
Publication Type: Trade Journal
Publication Acceptance Date: 11/28/2005
Publication Date: 5/1/2006
Citation: Hofgaard, I.S., Wanner, L.A., Hageskal, G., Henriksen, B., Klemsdal, S.S., Tronsmo, A.M. 2006. Isolates of microdochium nivale and m. majus differentiated by pathogenicity on perennial ryegrass (lolium perenne l.) and in vitro growth at low temperature. Journal of Phytopathology. Volume 154, Issue 5: 267-274. Interpretive Summary: Snow mold fungi grow under snow in winter, causing damage to grass in lawns, on golf courses, and to winter cereal crops, including winter wheat. The damage shows up in spring after snow melts as dead or dead-looking areas, with cottony growth of the fungus visible on careful inspection. Some grass and cereal varieties are more susceptible to snow mold than others, and plant breeders need reliable methods of testing for resistance to snow molds so that they can select the most winter-hardy varieties. Ideally, grasses or cereals are planted in the field to test their winter survival, but such field tests take several growing seasons, and differences in weather, growing conditions, and what snow mold fungi are present in different fields and different years produce variable field test results. Greenhouse tests are more reproducible, but still require many months to complete, and are therefore costly. We sought ways to make testing for snow mold resistance more reliable and less expensive. Snow mold fungi that are known to cause serious damage (aggressive isolates) are needed for both greenhouse and field tests. We compared several methods for evaluating the potential of different snow molds to damage plants (aggressiveness). Measuring growth of different fungi at low temperature was the simplest and quickest way to pick aggressive fungi, which researchers and plant breeders can use for more reliable greenhouse or field tests. Also, two methods for comparing snow mold susceptibility of grass varieties that are less time-consuming than traditional greenhouse tests were evaluated, but were not found to be reliable enough to replace greenhouse tests. The results of this research will be useful to grass and cereal breeders who want to improve winter hardiness in these crops.
Technical Abstract: The fungus Microdochium nivale causes pink snow mould damage on cereals and grasses in cold and temperate zones during winter. To better understand the basis for the great variation in aggressiveness between different isolates of M. nivale and to simplify the selection for aggressive isolates to use when screening for resistance to M. nivale in perennial ryegrass, we sought for traits correlated to aggressiveness. Aggressiveness, as measured by survival and regrowth of perennial ryegrass after infection with M. nivale isolates and incubation under simulated snow cover, was compared with growth of fungus on a rich medium (PDA), on detached wheat leaves and in perennial ryegrass plants during incubation under simulated snow cover by the use of PCR (polymerase chain reaction). The activity of fungal cell-wall degrading proteins secreted into a minimal medium containing ryegrass cell walls as carbon source was also measured. We found that aggressive isolates grew rapidly on detached leaves and on PDA at 2 C. Measuring fungal growth on PDA or on detached leaves seems therefore to be relatively simple methods of screening for potentially aggressive isolates. Aggressive isolates of M. nivale had an earlier increase and a higher total specific activity of -glucosidase compared to less aggressive isolates. These findings indicate that both vigorous growth of mycelium and a rapid increase, or a high specific activity, of cell-wall degrading enzymes at 2C, are traits characteristic of isolates of M. nivale regarded as aggressive on perennial ryegrass when incubated under a simulated snow cower at 2C.