Abstract

Rice is the second most important crop in the world after wheat, with more than 90 per cent grown in Asia. In order to evaluate the effects of cold stress in the period of germination and seedling and recovery percent of rice cultivars, two independent tests were performed in 2006-2007 in Rice Research Institution at Amol city. An experiment was conducted by split split plots within a randomized block design (CRD) with 54 caring composition, 3 replications and 6 cultivars were used. In this study, main plots were temperature, sub plots were length of stress and sub sub plots were cultivars. The levels of temperature including 10 oc (intense stress), 14⁰C (critical temperature) and 32⁰C (improving temperature, control) and levels of stress time 12, 24, 48 hours and cultivars of local Tarom, Domsiya, Hybrid, Nemat, Gerde, Unda were selected two by two based on quality of product and then performed in unit area and finally resistance against cold respectively. On the period of germination with decreasing temperature from 32⁰C to 14⁰C and from 14⁰C to 10⁰C, total decrease studied indices with exception of percentage of damage to seed are meaningful and similar reaction in recovery section of germination is obvious. In the period of seedling, we can see a meaningful decrease in significant level 1% about of decreasing temperature of total stress, percentage of damage to seedling, vigour of seedling. By increasing temperature in the period of stress of germination, there is a meaningful increase level 1% of total studied features with the exception of damage of seed. In the period of recovery of germination, there is a meaningful increase in significant level 1% of total studied features with the exception of damage to seed. In the period of stress of germination, there is a meaningful decrease at total features with the exception of sensitive to stress, percentage of damage to seedling and vigour of seedling and aceous recovery are similar in the period of seedling. By decreasing time of stress in the period of germination, there is a meaningful decrease by percent of damage total features with exception of rate of germination, percentage of germination. In the period of germination recovery, there is a meaningful increase in length if radicle, length of stem, percentage of germination and rate of germination and other features have meaningful decrease. In the period of seedling recovery, by decreasing time of stress, length of shoot, length of radicle, weight of wet, dry root and other features have meaningful increase. The effects of cultivar in total tests and stages, was significant level 1%. The results show that, feature of germination and length of stem and percentage of damage to seed in different cultivars are various. In the period of recovery, percentage of germination, rate of germination and percentage of damage to seeds, had correct criteria for selecting cultivars sensitive to cold stress. Low temperature can delay pitch and growth of transplant for more time. We can use height of shoot in rice as an index for determining of cultivars resistant to cold. According to these results, we decide precisely for re cultivate rice store or selecting to resistant cultivar by introducing Nemat cultivar in the period of germination and hybrid cultivar in the period of seedling aceous as resistant cultivar during occurring stress of cold.

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