Study effect time of terminal irrigation on grain yield, oil and some agronomic traits of canola cultivars (Brassica napus L.).

Introduction Drought stress is an important factors limiting growth and yield in crops that influencing 60% of agricultural lands in world (Shao et al., 2006). Rapeseed is one most important oil seeds in many arid and semi-arid regions, which often yield its limited due to water shortages and high temperatures during reproductive period (Ahmadi and Bahrani, 2009). The water deficiency can influence inversely the grain of canola but this effect depends on the genotype and, development and growth stage the plant adaption to the drought (Azizi et al., 1999). Increase percentage of seed and Silique abortion due to the reduction in provides photosynthetic products in the last season stress has been reported important reson reduction yield in rapeseed (Fanaei et al., 2013). Ahmadi and Bahrani (2009) reported that highest plant height, Siliques per plant, grain yield and oil yield were obtained in the full irrigation treatments, and the flowering was the most sensitive stage. Majidi, (2012) reported there is a significant variation in the tolerance to drought stress among cultivars and hybrids canola.  This experiment was conducted with the aim of determining most suitable time for the last irrigation for to minimize reduction grain and oil yield in canola cultivars. Materials and Methods In order to evaluate grain yield, oil and some agronomic traits of canola (Brassica napus L.) cultivars in final irrigation times an experiment as split-plot was conducted based on randomized complete blocks design with 3 replications in Zahak research station during three cropping seasons (2008, 2009 and 2010). Time of irrigation were at six levels: (I1=Last irrigation 5 days after end of flowering), I2= Last irrigation at 20 percent remained flowers in plants, I3= Last irrigation in start of color changing in siliqes of origin stem. I4= Last irrigation at 50 percent of Siliqueding.  T5= Last irrigation at 10 percent of color that changed in siliqes of origin stem.  I6= Last irrigation in flowering, these treatments were assigned as main plots and rapeseed cultivars at three levels including; (V1= Hyola 401 V2=RGS003 and V3=Sarigol) were assigned as sub-plots. Fertilizers were applied at ratio of 150 kg/ha super-phosphate triple, 200 kg/ha sulphate dipotash, respectively prior to sowing, along 180 kg/ha pure N based on Urea at ratio 40,30 and 30 percent prior to sowing, rosset and flowering start stages respectively. All other agricultural practices were performed when they were required. A random sample of five plants was selected from each plot in physiological ripening to estimate the different parameters. Data were analyzed by using MSTAT-C statistical package. Duncan Multiple Range Test was used to do mean comparisons Results & Discussion The effect Time of irrigation and cultivar were showed significant different on grain yield, components yield. Highest number of Siliques per plant and seed in Silique were produced in I1 (control) and I3 treatments with a mean 167 and 160 Siliques in plant and 22 and 21 seed in Silique respectively and lowest achieved in I6 treatment, with mean of 123 Siliques in plant and 18 seed in Silique.  It seems that water deficiet in during reproductive phase causing Silique decreases by increasing the flower and Silique abortion. Many researchers have reported that flowering and Silique development stages have a high sensitivity to drought stress (Ahmadi and Bahrani, 2009؛ Fanaei et al., 2013). The highest number of seeds per silique, seed in Silique and 1000 seed wieght belonged to Hyola 401 and RGS003. Among levels of irrigation time, the highest 1000 seed weight was observed in treatments I3 (3.6 g), I1 (3.5 g), I4 (3.48 g) and lowest 1000 seed weight with mean 2.97 g in I6 treatment. The highest grain yield was applied to I1 treatment, and I3 treatment, the highest grain yield was applied in I1, and I3 treatments respectively with mean of 3340 and 3132 kg/ha. In these treatments, enough provide of water during growth different stages due to positive effect on yield components caused improved seed yield of canola. It has been determined that the flowering and Silique development stages have a high sensitivity to drought stress and stress in these stages will caused to more reduction in grain yield (Ahmadi and Bahrani, 2009؛ Fanaei et al., 2013؛ Sinaki et al., 2007؛). Hybrid Hyoli 401 and RGS 003 had the highest grain yield with 3169 and 3029 kg ha-1. Conclusion Based on the result, it can be concluded terminal irrigation for high grain and oil yield could be conducted 5 days after end of flowering or in start of color changing in siliques of origin stem in both Hyola401 cultivar and RGS003 in Sistan and similar regions.