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In order to comparison of antioxidant enzymes and proline roles in drought tolerance of rapeseed, an experiment was conducted at the research field of Yazd Agricultural and Natural Resources Research Center in 2011-2012. In this study, three commercial rapeseed genotypes (GKH2005, Opera and Okapi) were examined for response to irrigation treatments such as non-stress conditions (control) and withholding irrigation from stem elongation, flowering and silique formation stages in four separate experiments based on randomized complete block (RCB) design. The results indicated that proline accumulation, activity of catalase and proxidase enzyme and lipid peroxidation index (content of malondealdehyde) were higher in drought stress treatments, but these amounts were different in three rapeseed genotypes. Maximum activity of antioxidant enzymes and low content of malondealdehyde was observed in GKH2005 compared with others, in drought stress conditions. Between these genotypes, GKH2005 produced the highest seed yield under non-stress conditions and withholding irrigation from stem elongation, flowering and silique formation stages as 3110, 1450, 1773 and 2510 kg.ha-1, respectively. These results showed that role of antioxidant enzymes on reduction of lipid peroxidation and increasing the drought tolerance is more than proline. Also, an effective antioxidant system along with lower malondealdehyde and high silique number per secondary branch had the greatest role to productivity maintenance of Rapeseed under drought stress conditions

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In order to evaluate the effect of different nitrogen fertilizer levels on physiological traits, plant height, yield components, and seed yield of rapeseed genotypes a split-plot experiment based on a randomized complete block design with three replications was carried out at the Baykola Agriculture Research Station, Mazaandaran during 2010-11. Four levels of nitrogen, as urea fertilizer, including of 0, 70, 140 and 210 kg ha-1 were considered as main plots and four rapeseed genotypes including of L7, Zafar, RGS003 and Hyola401 were considered as subplots. The result of analysis of variance revealed that the traits, including number of days to flowering, number of days to end of flowering, number of days to maturity, plant height, siliques pods per plant, seeds per silique, seed yield and oil yield were significantly affected by nitrogen levels. Genotype effect was significant effect on all the traits except seeds per silique. Hyloa401 and Zafar respectively with 3831.2 and 3893.7 kg ha-1 of seed yield, and also 1638 and 1591 kg ha-1 of oil yield were classified at the same statistical group. Non significant interaction effects of nitrogen fertilizer application and genotypes were achieved for all of the studied traits, indicated that the trend of variation of these traits due to nitrogen levels were similar in all genotypes. A significant positive correlation of seed yield with the other studied the traits, except days to flowering, indicated that increasing of nitrogen level application made increasing of the traits and finally seed yield.