Abstract
Perennial ryegrass (Lolium perenne L.), one of the most important forage grasses for temperate regions, exhibits lower winter survival than the other temperate grasses. Freezing hardiness is one of the primary factors associated with winter survival. The purpose of this study is to consider the freezing hardiness in relation to winter survival in diploid and tetraploid cultivars of perennial ryegrass. Twelve diploid and seven tetraploid cultivars were evaluated for viability over winter under field condition, and for freezing hardiness using the modified technique of Lorenzetti et al. The results obtained are summarized as follows. 1) Between-cultivar differences in winter survival were assessed for both diploid and tetraploid cultivars. Tetraploids had a higher degree of winter survival compared to the diploids. 2) Freezing hardiness varied greatly among the diploid cultivars, but not among the tetraploids. Tetraploids overall had lower freezing hardiness compared to the diploids. 3) These results suggest that the contribution of freezing hardiness to winter survival may be different between diploids and tetraploids. Therefore, the improvement of freezing hardiness in tetraploids would enhance the degree of winter survival in perennial ryegrass cultivars.
