Canola oil seed species currently hold the third position among oil seed crops and has lowest saturated fatty acids content (Ashraf and Mcneilly 2014). When commercial production was first considered in Iran, site location and planting date were thought to be the two most important cultural decisions. A long term drought stress effects on plant metabolic reactions associates with, plant growth stage, water storage capacity of the soil and physiological aspects of plant. Generally, the number of seed per plant, number of seeds per pod and also seeds weight are considered the yield components of canola (Angadi et al., 2003). A study by Kajdi and Pocsai (1993) on the effects of irrigation on 21 rapeseed cultivars showed that, as irrigation frequency increased, the seed yield increased as well. Indeed, they noticed the high seed yield only in the cultivars with high levels of erucic acid and glucosinolate. Moreover, it has been reported that drought or heat stress during flowering and seed filling stages could stop the flowering and caused decrease of seed formation, oil percentage and the seed yield to decrease (Johnston et al., 2002). If cultivars could be selected in a way that produce an acceptable economic yield in less watering condition and are more stress tolerant under the stress intensity conditions, they would be practically very useful for developing rapeseed cultivation in such regions.
In order to study the effect of delayed planting and drought stress on grain yield grain component, saturated and unsaturated fatty acids, oil content and glucosinolate of seeds and proline content of rapeseed, a field experiment was conducted as split-plot arrenged in a Randomized Complete Block Design (CRBD) with three replication in Seed and Plant Improvement Research Institute of karaj in 2014-2016. Experimental treatments were included sowing dates in two levels included: 20th of October (normal cultivation) and 5th of November (delayed cultivation), Irrigation in 2 levels includes: normal Irrigation (control) and drought stress (irrigation withholding in pod formation) as well as hybrids and hybrids Rapeseed autumn included: Neptune, Elvise, Okapi, Tassilo, GKH0224, GKH2624 and GKH3705.
The results of the experiment showed that planting date, irrigation and cultivar were significant on all traits Except for eicosenoic acid, Results showed that delaying the planting date decreased pod number per plant, 1000-grain weight yield, oil content, eicosenoic acid proline, whereas behenic acid and seed glucosinolate were increased. The highest oil content (45.59%) was in normal irrigation and normal cultivation, And the lowest (42.16%) was observed in irrigation withholding in pod formation stage and delayed cultivation. The highest content of proline (21.59 mg.g. Fw) was observed in normal cultivation and GKH3705 cultivar. The cultivar of GKH3705 was the most appropriate in terms of yield and its components, oil content, saturated and unsaturated fatty acids and glucosinolate of seeds. According to the results, it seems that normal cultivation and GKH3705 cultivar under without stress and drought stress can be recommended as the best treatment for the benefit of rapeseed production in the Karaj region.
According to the results of this experiment, the most suitable planting date for the studied cultivars of canola is 20th of October in Karaj area. Among the cultivars under study, GKH3705 also produced the highest grain yield in normal and delayed planting, as well as in normal irrigation and stress conditions. In terms of grain and oil production potential and the composition of unsaturated fatty acids are in the optimum level.
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