Evaluation of the agronomic characteristics and some physiological traits of canola varieties under drought stress

In order to evaluate the agronomic characteristics and some physiological traits of canola varieties under drought conditions, separate experiments were carried out at the Research Field of Yazd Agricultural and Natural Resources Research Center in 2011-2012. Each experiment was conducted in a randomized complete block design with three replications. In the first experiment (control) that was conducted under optimal irrigation, plants were irrigated based on 80 mm evaporation from pan class A at all stages of plant growth, in the second experiment, drought stress was applied at stem elongation up to maturity stage, in the third experiment, drought stress was performed at flowering up to maturity stage and in the fourth experiment, drought stress was performed at silique formation up to the end of maturity stage using three canola varieties including GKH2005, Opera and Okapi. The results of combined analysis showed that withholding irrigation started at stem elongation, flowering stage and silique formation reduced the silique number in the main stem by 44, 34 and 9 %, silique number per branches by 60, 34 and 17 %, seed number in silique per main stem by 62, 35 and 5 %, seed number in silique per branches by 73, 46 and 11 %, 1000- seed weight by 19, 28 and 26 % and seed yield by 62, 51 and 27 %, compared with the control conditions, respectively. The greatest grain yield was obtained from the control experiment as 3110 kg/ha and followed by withholding irrigation from silique formation, flowering stage and stem elongation with corresponding values of 2510, 1773 and 1450 kg/ha, respectively. Drought stress reduced the stomatal conductivity, relative water content (RWC) and cell membrane stability, whereas SPAD value was higher under drought conditions as compared with the control experiment. Under drought stress among studied cultivars, GKH had the maximum silique number, seed number in silique and seed yield due to the least electrolyte leakage percentage, higher stomatal conductivity and relative water content (RWC). The overall results of the experiments showed that withholding irrigation from silique formation owing to the reduction in irrigation frequency and efficient use of it in summer crops irrigation accompanied with the employment of drought tolerant varieties can be effective in increasing productivity and canola cultivation areas in arid and semi-arid regions.