Rice is a plant that is sensitive to low temperature stress. This study aims to identify a suitable technique to estimate rice (Oriza sativa L.) cold tolerance at the germination stage and identify the variability among 12 genotypes. Cold tolerance was evaluated in two experiments: in experiment I, seeds were germinated under two conditions; 28 days in 13°C and seven days in 28°C; in experiment II, seeds were germinated at 72 hours with 28°C, 96 hours at 13°C and again 72 hours at 28°C. In experiment I percentages of reduction in radicle and coleoptile length and germination index were measured. In experiment II radicle and coleoptile regrowth after the cold period were measured. Results showed that low temperature effects in both experiments were varied among studied genotypes. Germination index in PR27137-CR153 and Hashemi genotypes had the highest and the lowest level respectively. Percentage of reduction in radicle length by low temperature was varied from 54 to 85% and the range of reduction in coleoptiles length was 31 to 72%. In experiment II, radicle regrowth values varied from 3.5 to 21.7 mm, and PR27137-CR153, Khazar, Hasani and Gil2 were four genotypes with high radicle regrowth, more than 18 mm. PR27137-CR153, Khazar and Hasani showed the highest coleoptiles regrowth of over 18.5 mm.

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