Evaluation of rice germplasm to low temperature stress during germination and seedling stages.

Rice is a tropical and sub-topical crop، which is sensitive to low temperature. This study was conducted in two different experiments during two consecutive years. In the first experiment based on among 200 Iranian cultivars 26 cultivars selected for study. The seeds of selected cultivars were studied in 4different thermal levels including 5, 10, 15 and 25 (control) factorial design with based on CRD with three replications. Results showed that, low temperature reduced the survival and seedling growth. However, germination percentage, seedling vigor, shoots and root length were the best characteristics for selection of tolerant genotypes. Among the genotypes, Gerdeh Zanjan, Anbori ghermez were the tolerant genotypes, while Hovaizeh was the most susceptible genotype. Also, results showed that, during seedling stage Gerdeh, Onda and Rasmi were the most tolerant genotypes to low temperature stress. In the second experiment, 77 rice genotypes including 49 line of International Rice Cold Tolerance Nursery (IRCTN 2005) and 28 Iranian rice were tested in split plot arrangement using completely Randomized Design (CRD) in phytotrone for screening and monitoring of their performance. International Rice Research Institute (IRRI) scoring system used for ranking of genotypes at normal and stress conditions. Chlorophyll fluorescence attributes, Chlorophyll content (SPAD values) as well as root and shoot dry weight was measured. Results showed that in low temperature 13/10 oC (night/ day, respectively) qP, ETR,_PSII, Fv:Fm, SPAD value and vigor of seedlings as well as root and shoot dry weight significantly reduced as compared with normal temperature 22/29 oC (night/day, respectively). Among genotypes of IRCTN No. 33, 34, 36 and 44 (the Philippines) had the highest values and stability of Fv:Fm and_PSII parameters in low and normal temperatures while Hoveizeh (from Iran) had the lowest tolerance to low temperature. In addition, there was a highly significant correlation between root dry matter and vigor, showing sensitivity of root to low temperature. Therefore, this parameter could be used as a criterion for selection of tolerant cultivars and genotypes to low temperature stress.