Effect of Supplemental Irrigation on Seed Yield and Yield Components of Canola (Brassica napus L.) Cultivars in Gonbad Region of Iran

In canola (Brassica napus L.), such as in most plant species, drought stress affects sink and source relationship as well as photosynthates assimilation, hence reduces seed yield. To evaluate the effect of supplemental irrigation on seed yield and yield components of canola cultivars, an experiment was conducted in 2004–2007 growing seasons at Agricultural Research Station of Gonbad, Iran. The experiment was arranged as factorial in randomized complete block design with three replications. Experimental factors included four irrigation levels (1-without irrigation, 2-irrigation in flowering stage, 3-irrigation in seed filling stage and 4-irrigation in flowering + seed filling stages), and three canola cultivars (Hyola401, RGS003 and Option500). Combined analysis of variance showed that the effect of year was significant on all studied traits. Mean of pod number plant-1 in without irrigation, irrigation in flowering, irrigation in seed filling and irrigation in flowering + seed filling stages was 150, 145, 163 and 143 pods in 2004-05, 85, 113, 104 and 108 pods in 2005-06, and 73, 95, 95 and 106 pods in 2006-07 growing seasons, respectively. The number of sunny hours during seed formation was a determinant factor of seed production. Mean seed number pod-1 in the first, second and third growing seasons was 15.1, 21.6 and 13.4 seed, respectively. In different growing seasons, the effect of irrigation on seed yield was different, and depended on rainfall at irrigation time. Mean of seed yield in without irrigation, irrigation in flowering, irrigation in seed filling and irrigation in flowering + seed filling treatments was 3283, 3520, 3709 and 3890 kg ha-1 in 2004-05, 3093, 3339, 3047 and 3922 kg ha-1 in 2005-06, and 2802, 2494, 2687 and 2804 kg ha-1 in 2006-07 growing seasons, respectively. Hyola401 had higher seed number pod-1, higher seed weight and the highest seed yield. Mean of seed yield of Hyola401, RGS003 and Option 500 cultivars was 3984, 3552 and 3266 kg ha-1 in 2004-05, 4035, 3109 and 2908 kg ha-1 in 2005-06, and 4093, 2500 and 1497 kg ha-1 in 2006-07 growing seasons, respectively. Results of this study showed that RGS003 is a suitable cultivar to be grown side by side of Hyola401 in Gonbad region of Iran.