Evaluation of Cold Tolerance in Rapeseed (Brassica napus L.) Genotypes at Seedling Stage and its Association withMicrosatellite Markers

Cold is one of the most important abiotic stresses, limiting growth and yield of rapeseed in cold prone areas in Iran. In order to study the cold tolerance of selected popular rapeseed genotypes in Iran and its relationship with SSR markers, this research was conducted in two separate experiments. In the first experiment 24 genotypes of rapeseed were exposed to 25˚C (as control) and 5˚C (as cold stress) treatments at seedling stage. Ten days after implementing cold treatment (about 30 days after sowing), an array of morphological and physiological characteristics were measured. A wide genetic variation was observed among genotypes for the measured traits. The maximum of the genetic diversities of morphological characters in cold and non-stress conditions  (60.77 and 62.22, respectively) was observed for the root dry weight. Cluster analysis classified genotypes into four groups based on the measured characters and CR3198 was the genotype identified as cold tolerant at seedling stage. This genotype indicated the greatest root length (18.25 cm), root dry weight (0.3 g), SPAD value (39.71) and Fv/Fm (0.79) and the smallest electrolyte leakage (13.02) under cold stress (5˚C) treatment. Cold tolerant genotypes were characterized by a high seedling vigor. In the second experiment relationships between ten pairs of SSR markers and cold-related traits were investigated. Results of binary logistic regression showed that some SSR markers were associated with shoot and root dry weight and cold stress tolerance index. Three SSR markers including Na10-B08, Na12-E09 and Ra2-E11 were found to be related to cold stress tolerance index of rapeseed at seedling stage. In general, results of this investigation can be used for improving cold tolerance of rapeseed seedlings in breeding programs.