عنوان مقاله [English]
In order to evaluate freezing tolerance of some clover species as well as planting date and acclimation period effects on plant tolerance, an experiment was conducted in 2012-13 in Faculty of agriculture, Ferdowsi University of Mashhad in completely Randomized Design with factorial arrangement and four replications. Experimental factors included two planting dates (late September and late October), four clover species (red clover T. pratense, white clover T. repense, Persian clover T. resupinatum (autumn species) and crimson clover T. incarnatum (spring spieces) and eight freezing temperatures (0 (control), -3, -6, -9, -12, -15, -18, -21ºC). Electrolyte leakage percentage of leaf and crown was measured and used to determine lethal temperature for 50% of plants (LT50el(l) and LT50el(c) for leaf and crown, respectively). Results indicated that interaction of planting dates, species and freezing temperatures on electrolyte leakage of leaf was significant in a way that a lower mean of this parameter was observed in autumn species in first planting date compared to the second planting date but the reverse was found in spring species. Decreasing temperature to less than -12 and -15 ˚C resulted in an increase in electrolyte leakage of crown in red and Persian clovers, and white and crimson clovers, respectively). The least LT50el(l) in first planting date was found in red and Persian species and the highest in crimson species while in the second planting date, the lowest mean was observed in Persian and crimson and the highest in red species.
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