Abstract
The degree of frost hardiness, the carbohydrates content, and the degree of resistance to Sclerotinia snow blight disease (Scleotinia borealis Buback & Vleugel) were compared in eastern Hokkaido among 27 cultivars collected from various geographical regions. The frost hardiness of seedlings of cultivars determined by the artifical crown freezing method in the beginning of winter, were positively correlated with the mean temperature in January of their breeding sites (r=-0.707). The increasing order of content of carbohydrates fractions accumulated in seedling, was reducing sugars (RS)<nonreducing sugars (NS)<total sugars (TS)<Fructosans (FS)<water soluble carbohydrates (WSC: TS+FS). All of these fractions except the RS showed significant correlations with both of the frost hardiness and the dry matter percentage. Higher correlation coefficients were obtained between the WSC content and the frost hardiness (r=+0.673), and between the WSC content and the dry matter percentage (r=+0.710). Resistance to Sclerotinia snow blight disease of mature plants of 17 cultivars was evaluated at the end of snow cover with the percentage of tillers which were damaged by Sclerotinia. The percentage of the damaged showed significant negative correlation with the frost hardiness (r=-0.617), the NS content, the TS content, the FS content and the WSC content (r=-0.657). North European, North American and Hokkaido cultivars were more resistant to Sclerotinia snow blight disease than others. The WSC content seemed to be a useful measure both in breeding of winter hardy cultivars and in cultivation of orchardgrass of soil freezing area, and the dry matter percentage could be used as a measure of the WSC content.
