Varietal differences in cold tolerance of temperate grasses

Abe, J.

Varietal differences in cold tolerance of 5 important temperatre grasses, timothy, meadow fescue, cocksfoot, tall fescue and perennial ryegrass, were assessed by means of the modified laboratory technique of Lorenzetti et al. Seedlings artificially hardened were exposed to -12.degree. C for 16 h for 4 grasses excluding cocksfoot which was subjected to -10.degree. C for 16 h. Cold tolerance of seedlings was ranked in the following order of decreasing tolerance, based on percentage plant survival: timothy (98-89%) .gtoreq. meadow fescue (94-68%) > tall fescue (50-25%) .gtoreq. perennial ryegrass (34-11%) > cocksfoot (73-16% at -10.degree. C). These freezing treatments were suitable for meadow fescue and cocksfoot, while the treatment with -12.degree. C for 16 h was too mild to detect differences among timothy varieties and was too severe for tall fescue and for perennial ryegrass, showing that it is necessary to improve the freezing methods. Cold tolerance in adult plants of temperate grasses gives the same rank as in seedlings mentioned above with the exception of cocksfoot, whose cold tolerance is at least greater than that of perennial ryegrass. This suggests that cocksfoot should increase tolerance with time to a greater degree than perennial ryegrass and/or the others. The most important factor common to these grasses responsible for cold tolerance is winter cold in the original habitat of breeding materials. In general, the Scandinavian and the Canadian varieties were hardy, the Japanese ones moderate, and the southern European and the British ones tender. The varieties classified as the most tender in this experiment may be vulnerable to winter cold, so that caution should be used when introducing them to the eastern Hokkaido, where the winters are the most severe in Japan.