Effect of temperature on cold dehardening of Lolium perenne L. seedlings

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Abstract
SUMMARY: Cold dehardening responses of seedlings of three cultivars of Lolium perenne L. (Premo, S.23 and Grasslands Ruanui) were studied in different temperature regimes following hardening at 2 °C. Seedlings of the three cultivars dehardened rapidly at 15 °C after partial hardening for 4 days, whereas there was a lag before dehardening occurred in seedlings of Premo and S.23 which were hardened for 28 days. At 10 °C dehardening did not occur in Premo and S.23 and occurred only slowly in Grasslands Ruanui. Alternating temperature regimes of 15 °C(day): 2 °C (night) gave increased levels of hardiness when the daily period of exposure to 15 °C was 8 h but only maintained the level of hardiness when it was extended to 16 h.A tentative scheme of threshold temperatures for hardening and dehardening is proposed.