Appraisal of physiological and biochemical selection criteria for evaluation of salt tolerance in canola (Brassica napus L.)

Of Brassica species, canola (Brassica napus L.) is potentially important due to its good quality edible oil and potential to grow on salt affected areas. A greenhouse experiment was conducted to screen 34 local and exotic accessions of canola (Brassica napus L.) for salt tolerance and to identify suitable traits as selection criteria. Six week-old hydroponically grown plants of canola cultivars were subjected to 0 or 150 mM NaCl for five weeks. Various physiological and biochemical traits such as net CO2 assimilation rate, stomatal conductance, transpiration rate, water use efficiency, leaf proline, leaf glycinebetaine, leaf Na+, leaf K+ and leaf K+/Na+ ratio, leaf osmotic potential and leaf relative water content were measured. All canola cultivars were ranked on the basis of relative salt tolerance using various physiological and biochemical attributes and then correlated with plant salt tolerance (plant growth) to identify the suitable selection criteria. Thus, the 34 lines were possible to categorize into three groups, i.e., salt sensitive, moderately salt tolerant, and salt tolerant. Dunkeld followed by Con-II, Rainbow were highly salt tolerant, while Westar, Balero, Oscar, RGS 003, Option-500 and Cyclone were salt sensitive. However, cvs BLN-877, Haanza, Goliath, and Olga were also considered potential candidates as salt tolerant cultivars. According to the analysis of linear regression of the scores of the physiological traits against those of plant growth, except leaf K+, leaf osmotic potential and RWC, all physiological and biochemical traits were positively related with their salt tolerance. However, A and gs were found as the most suitable determinants. Overall, photosynthetic capacity, proline and GB accumulation ability, and ion discrimination can be used as potential biochemical or physiological selection criteria for salt tolerance in canola. Although leaf Na+, leaf K+/Na+ ratio, proline and GB accumulation were positively related with salt tolerance, the strength of relationship was week.