Study of salinity tolerance in rapeseed

Eight diverse Brassica napus genotypes and their 28 F1s were evaluated in nonsaline and saline environments in sand culture. Combined analysis based on two salinity levels revealed significant salinity-level effects for shoot dry weight, plant height, root length, and ions in shoot tissues, including potassium (K), sodium (Na), Ca/Na, and K/Na. Salinity had no significant effect on shoot calcium (Ca) concentration. Stress intensity (SI) estimates, its larger values indicating the more severe stress intensities, were high for all studied traits except for root length, Ca, and Na. The mean of Na in a saline environment was more than seven times the mean in a nonsaline environment, therefore SI was not calculated for this parameter. Low estimates of SI for root length and Ca indicated the effects of a saline environment for these two traits were less than for the other traits. Significant interactions of genotype and salinity levels were observed for all studied traits. The results of factor analysis based on minimum eigenvalue revealed two factors for eight studied traits in a saline environment. Factor one was detected as a nutritional trait in which Ca, K, Ca/Na, and K/Na had a high coefficients factor loading. Factor two was detected as morphological traits. The results of factor analysis indicated that selection for nutritional traits should be more efficient than selection for morphological traits and, specifically, that selection based on K and K/Na should be more efficient than Ca and Ca/Na. Significant positive correlations were found between shoot dry weight and other traits, including Ca, K, Ca/Na, and K/Na in a saline environment; therefore, these ion relations can be used as good selection criteria for improving shoot dry weight. On the basis of low estimates of the tolerance index (TOL) for shoot dry weight (its large value represents more sensitivity to stress), it was concluded that the genotypes including BL2, Ceres, Shiralee, Falcon x BL2, PF7045/91 x Ceres, and BL2 x Ceres had suitable salinity tolerance in early stages of growth.