The Effect of Planting Date and Late Season Drought Stress on Eco-Physiological Characteristics of the New Varieties of Canola (Brassica napus L.)

Development of new canola (Brassica napus L.) varieties need effective tools to monitor characterizes association in yield and its components. Although, determination of the response of canola cultivars to environmental variables is one of the principal of agriculture planning to achieve maximum qualitative and quantitative yield. Drought stress and planting date are the most important factor which limit yield production in arid and semiarid regions. Iran is considered as the arid and semiarid with average rainfall of 250 mm. On the other hand, 33% of agricultural land is devoted to dry cultivation. Changing plant date will change yield and product quality by affecting on vegetative and reproductive growth period and balance between them. In order to study the responses of four winter canola cultivars to late season drought stress and different planting dates on physiological, morphology characteristics and yield, a split factorial experiment was carried out in Randomized Complete Block Design with three replication in 2011-2012 in Karaj province. Planting date in two levels, normally sowing dates and delayed planting date and irrigation in two levels, normal and cutting off irrigation from pod stage to next, both in main plot and four cultivars included (Trapper, Makro, Smilla and Agamax) in sub plot. Drought stress was applied by control of irrigation during the pod lengthening stage. Thus, drought was applied by withholding water when the first pod appeared at the beginning of pod filling (April 27th). At this stage, chlorophyll and total sugar solution content was measured as index of drought stress damage. Eleven traits were measured on 10 random plant/plot at physiological maturity stage (June 24th). The traits were plant height, no. of branches/plot, number of pods /plant, pod length, number of seeds/plant,1000-seed weight, seed yield, biomass yield, oil percentage, oil yield and harvest index. The results showed all characteristics except harvest index, significantly (p≥0.05) were influenced by planting date, drought and cultivars. Interaction of sowing date in irrigated was significant in attributes of soluble carbohydrates, plant height, number of pods per plant and oil content. The triple effect was significant only in the concentration of soluble carbohydrates. Due to late planting and irrigation disruption, increasing in soluble carbohydrates and reducing the concentration of chlorophyll was occurred. The yield components of canola decreased because of delays in planting and irrigation disruption which leads to lower grain and canola oil yield. Among cultivars, two cultivars Trapper and Agamax narrowly to each other had better outperformed comparing to Smilla and Marko. Using different sowing dates can change the time of plant growth and development, helping the plant to survive better, under the stress of heat and drought. Water stress along with end of the season delayed planting, reduces yield components and increasing concentrations of soluble carbohydrates. Non-significant interaction effects of planting dates and cultivars for seed and oil yield indicated that yield reduction of the cultivars in late planting dates had similar trend. Drought not only causes dramatic loss of pigments but also leads to disorganization of thylakoid membranes. Therefore reduction in chlorophyll contents is expected. The sowing date may influence plant growth that can be attributed to the favorable climatic conditions (rain and temperature). Correlation between drought tolerance and yield in all cultivars, identify the most suitable indicators for monitoring drought tolerance cultivars. According to these results, Trapper and Agamax can be recommended for semiarid regions due to maximum seed and oil yield among the stress and non-stress condition. Delayed planting decrease seed oil percent, grain and oil yield of Smilla and Makro than the other cultivars.