Breeding winter hardy grasses

Summary Perennial grasses are vital for Norwegian agricultural production. The nature and extent of winter damage on grasslands is highly dependent on climatic conditions, and determines both persistency and yield. Physical stresses such as frost and ice encasement predominate in coastal regions with an unstable winter climate, while biotic stresses such as low temperature fungi are more common in the inland regions. Development of hardening depends on plant adaptation and climatic conditions during autumn and winter. New winter-hardy cultivars should be bred for wide adaptation to winter stresses. The genetic background for the most important character, freezing tolerance, seems to be of polygenic nature with mainly additive gene action. Selection for increased freezing tolerance has been effective over generations in grasses, and in most grass species ample variation still exists to be exploited by breeding. However, in some species like perennial ryegrass, modern biotechnological methods should be used to improve freezing tolerance and winter hardiness.