Effect of Salt Stress on Growth and Ion Distribution of Rape Genotypes (Brassica napus L.) Differing in Salt Tolerance

To examine the response of three rapeseed varieties to salinity stress, a pot experiment was conducted in a glasshouse using a factorial experiment based on a randomized complete block design with three replications. Three levels of NaCl (0, 100 and 200 mM NaCl) were imposed as the salinity treatments at root establishment (leaf 4) stage. In this study, sodium (Na+) and potassium (K+) concentrations and K+/Na+ ratio were compared in different tissues in three  varieties of rapeseed (PP-401-15E, Hyola401 and Hyola60) known to differ in salt tolerance, 30 days after salt treatment commencement. Effect of salinity was significant on all measured characters. The decline in shoot and root biomass and grain yield of salt sensitive genotype (PP-401-15E), were higher than those of the salt tolerants (Hyola401 and Hyola602) in response to salt stress. It seemed that the decrease in shoot biomass was primarily due to the osmotic effect of the salt, rather than the Na+-specific effects. The salt tolerant genotypes accumulated smaller quantities of Na+ in the shoot and root, indicating that the degree of salt tolerance in these genotypes depend upon the degree of salt exclusion from the plants. The salt sensitive genotype maintained a smaller K+/Na+ ratios in youngest fully expanded leaf than the salt tolerant genotypes. The ion partitioning capability in rape, thus, can considerably improve its salt tolerance. Relative membrane permeability was more notably increased in 200 mM NaCl in sensitive genotype (PP-401-15E) than the tolerant ones, and hence, can be used as selection criteria for improving salt tolerance