Given prevalence of clover cultivation in Iran, it is likely to face with environmental stresses, such as cold stress for this plant. Therefore, the present study was done to investigate the relationship of carbohydrate concentration and morphological characteristics of roots with cold stress tolerance in clover genotypes using a split-plot design in time. Planting date at three levels as the main factor, 10 clover genotypes as a sub-factor, and also cutting time at three levels as a sub-factor

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... were all considered in a randomized complete block design with four replications in two crop years. With delay in planting, root length, root weight, crown diameter, and crown weight were decreased in clover genotypes and root –to- shoot ratio was increased. Red clover and Persian clover (late maturity) had higher concentrations of soluble carbohydrate, fructose, glucose, and starch in the roots, while Persian clover (one cutting) and crimson clover showed the lowest concentrations. Delay in planting caused a 13% decrease in total soluble carbohydrate concentration and glucose, fructose, and starch concentration was decreased by 20, 21, and 9%, respectively. Slope of the sugar storage curve between the two stages of winter dormancy and spring regrowth was milder in the red, berseem, Persian (one cutting), and crimson clover, respectively and root sugar storage curve was used less. Slope of carbohydrate storage curve was higher in berseem and crimson clover from regrowth until the first cutting, and because of this rapid growth, these genotypes can be used in the areas with low-stress temperatures within this time range.