Effect of elevated CO2, drought stress and ultra violet on quantity and quality characteristics in two autumn cultivars of canola (Brassica napus L.)

Drought, UV radiation and increased carbon dioxide concentrations are the most important abiotic stress factors threatening human food security. In the recent decades, several studies have been carried out for understanding the individual effect of each of these factors on crop growth and production. However, there is no comprehensive study encompassing the interaction between these factors on qualitative and quantitative traits of canola. Accordingly, an experiment was conducted to evaluate the role of irrigation levels, CO2 concentration levels and ultraviolet levels on two autumn cultivars of canola. the experiment was carried out as a Randomized Complete Block Design with a Factorial arrangement with three replications in 2013. The factors in this study included the two cultivars ‘Okapi’ and ‘Talaye’ and the irrigation strategy had two levels: normal irrigation as the control and drought stress from the flowering stage to physiological maturity (irrigation on base 60 percent of field capacity). CO2 concentration was allotted at two levels, namely ambient (400 μmol mol-1) and enriched (900 μmol mol-1) carbon dioxide (CO2) concentrations and ultraviolet radiation at three levels as follows: ultraviolet-A radiation (18μWcm-2 intensity), ultraviolet-B radiation (25μWcm-2 intensity) and ultraviolet-C radiation (40μWcm-2 intensity) respectively. In this study, the number of pods per plant, number of grains per pod, one thousand grain weight, grain yield and oil yield, flavonoid pigment, anthocyanin pigment and fluorescence were all determined. The results showed that irrigation strategy significantly affected all the studied traits except for oil yield. Water stress significantly decreased the number of siliques per plant, number of seeds per silique, 1000-seed weight, the final yield and fluorescence but increased flavonoid and anthocyanin pigments. An increase in the CO2 level was not significant on silique number per plant, flavonoid and anthocyanin content but it significantly increased seed weight, final yield, oil yield and fluorescence in plants. The effect of UV radiation was significant on all studied traits, and UV radiation decreased all of the traits in this experiment except for flavonoid and anthocyanin pigments. Triple interaction between experimental factors was significant on seed yield and oil yield at 0.01 and 0.05 probability levels, respectively. Comparison of means indicated that either under full irrigation conditions or water stress conditions the maximum seed yield was related to 900 ppm CO2 and UVA treatment. Overall, elevated CO2 could ameliorate the adverse effects of UV radiation in 1000-seed weight, the final yield, oil yield and fluorescence and improve these traits.