A COMPARISON OF COLD HARDINESS AND ICE ENCASEMENT TOLERANCE OF TIMOTHY GRASS AND WINTER WHEAT

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Abstract
In the falls of 1979 and 1980 Salvo timothy grass (Phleum pratense L.) showed cold hardiness similar to Norstar winter wheat (Triticum aestivum L.) but significantly greater hardiness than Fredrick winter wheat. Ice tolerance of Salvo, with LI50 values of 29 and 45 days in the 2 yr, was more than twice that of the wheats. In controlled environments, seedlings of three timothy cultivars showed relatively low cold hardiness, but about threefold greater ice tolerance than the wheats. An Icelandic timothy cultivar, Korpa, showed greater ice tolerance than the Norwegian Engmo, and the Canadian cultivar Salvo. Fredrick wheat, and Korpa timothy cold hardened at a similar rate for 4 wk, but Korpa continued to harden to − 18 °C up to 6 wk of low temperature growth. Korpa rapidly attained a high tolerance to ice encasement in 2 wk of low temperature growth while Fredrick attained relatively low ice tolerance reaching a maximum at 3 wk of growth. There is little association between cold and ice tolerance in timothy, and there is a major difference in the ice tolerances of timothy and winter wheat. This high ice tolerance is likely to be a major cause of the superior survival of timothy in conditions of high winter stress. Key. words: Triticum, Phleum, acclimation, resistance, low temperature, frost