Freeze Tolerance of Perennial Ryegrass and Implications for Future Species Distribution

Poor winter hardiness is one of the factors limiting the use of the palatable and productive cool‐season forage grass perennial ryegrass ( Lolium perenne L) in the northeastern United States. We compared freeze tolerance among seedlings of 13 commercial cultivars of perennial ryegrass in a controlled environment chamber. After a 14‐d acclimation period, plants were chilled to −10, −15, or −20°C for 1 h, then gradually warmed. After 36 d, surviving plants were counted then harvested and weighed. Mortality rate varied significantly among cultivars (0–13% at −10°C, 47–100% at −20°C). The temperature at which 50% of plants would die (LT50) ranged from −12.9 to −20.8°C. Hardiness ratings provided by the breeder did not match well with LT50 except for the most hardy cultivars. Extreme minimum temperature predictions were extracted from regional climate forecasts for three 30‐yr periods: baseline (1960–1989), short‐term future (2015–2044), and long‐term future (2070–2099). During the baseline period, only 2 to 33% of the northeastern United States was warm enough for these cultivars to survive during at least 50% of winters. Potential tolerable area may increase to 57 to 88% by 2099. Although other factors such as snow cover and variability of winter temperatures affect winter survival in the field, breeding for freeze tolerance has increased the potential extent of perennial ryegrass. Further improvements and the changing climate may greatly increase the utility of perennial ryegrass as a forage in the northeastern United States.