Abstract
Perennial ryegrass (Lolium perenne L.), one of the most important forage grasses for temperate regions, exhibits lower winter survival than other temperate grasses. Freezing hardiness is one of the primary factors associated with winter survival. The objectives of this study are to elucidate the differentiation in freezing hardiness among cultivar groups of perennial ryegrass, and then to examine the relationships of freezing hardiness with some agronomic characters. Freezing hardiness was assessed for 152 diploid and 25 tetraploid cultivars released in various nations using the crown-freezing test. Survival rate (%) after freezing ranged from 0% to 100% among the cultivars. Diploids overall had higher freezing hardiness compared to the tetraploids. Freezing hardiness also varied among the cultivar groups based on the utility type ; turf-types were the most hardy, the forage-types were the most sensitive to freezing, while the dual-purpose types were intermediate. Hardy cultivars tended to be small in plant height, leaf width and forage yield. It was also diverse among the cultivar groups based on nations of origin ; the cultivars released in U.S.A. were more hardy than the ones released in Europe.
