Evaluation of Cold Tolerance in Rapeseed (Brassica napus L.) Using Stress Tolerance Indices

In order to study the response of 120 genotypes of rapeseed (including 100 hybrids and 20 parents) in terms of cold stress tolerance, an experiment was conducted in α-lattice design with two replications under normal (September) and late sowing (October) conditions during two years. Combined analysis of variance showed that genotypes were significantly different at 1% and there was a significant genetic variation among the studied genotypes. In addition, there was a significant difference between the environments (normal and late sowing) at 1% in both years and the effect of late sowing on the yield of rapeseed was different from that of normal sowing. Total mean of seed yield in non-stressed condition was 4.9 ton/ha and in cold stress condition was 2.72 t/ha (34% reduction compared to normal sowing conditions). Principal component analysis (PCA) using six indices of cold stress tolerance (MP, GMP, HARM, TOL, SSI and STI) showed that the first two components justify about 99.85% of the variation in the population. The biplot of first and second components divided the genotypes into four different groups and identified 29 high yielding and cold tolerant genotypes. Similarly, cluster analysis divided the genotypes into four different groups and grouping of genotypes using cluster analysis showed good agreement with the results of principal component analysis. Correlation between different indices of stress tolerance and yield in stress (YP) and non- stress (YS) condition showed that TOL and SSI had positive correlation with YP and negative correlation with YS. Furthermore, the four indices of MP, GMP, HARM and STI showed positive and significant correlation with yield in both stressed and non-stress conditions. The results of this study showed that the STI index has a high efficiency in selection of rapeseed genotypes for cold tolerance and can be successfully applied in breeding programs.