Study of ecophysiology of reaction of wintering rapeseed (Brassica napus L.) cultivars to end of season drought stress in delayed culture

Rapeseed (Brassica napus L.) is one of the most important oilseed plants that has been ranked third in the oil production after soybeans and oil palm (Oil World, 2012). Drought stress is the most important limiting factor in the production of agricultural products in arid and semiarid regions (Debaeke and Aboudrare, 2004). Although water shortage in many developmental stages reduces the yield of rapeseed, the negative effects of stress during flowering and growth stages are much more pronounced (Sinaki et al, 2007).

In order to study the ecophysiology of new winter varieties of rapeseed (six lines ready for introduction and Ahmadi's native species as control), the drought stress of the end of the season was observed in two latent cultivation conditions including the usual sowing date (11th of October) and the latent planting date (26th of October) and Irrigation was carried out in two levels including irrigation (control) and irrigation cut off from stepping stage to a factorial split plot design in a randomized complete block design with three replications in two years of cultivars 2015-2016 and 2016-2017 at the Research Institute for Correction And planting seedlings and seeds of Karaj. Planting dates and irrigation will be the main factor and the cultivars of the sub-cultivar. Data analysis was performed using SAS software. First, the Bartlett test is performed and then the combined analysis of the two-year data is tested. Comparison of mean of main effects by LSD method at 5% level and in the case of meaningful interactions, cutting and comparing the meanings were done using L.S.Means test. The results showed that the main effect of cultivar, and the effects of year on planting date and cultivar, were significant on planting date on seed oil.

Results showed that in the first year and sowing date of 11th of October, the highest seed oil was obtained in the amount of 24.31%. The lowest amount was obtained in the second year and the sowing date of October 26th. In general, the seeding date of Oct. 11, in both years, had more seed oil yields. Regarding the interaction between sowing date and cultivar, results showed that the highest seed oil at the planting date of 11th of October and L72 was 54.44 percent. The lowest values were obtained on the 26th of October and the HW3 cultivar. In general, L72 had more seed oil in both dates. The results showed that the main effect of year, main effect of irrigation, main effect of cultivar, main effect of sowing date and interaction effects of planting date on cultivar on seed yield was significant. In the second year, oil yields more than the first year. In irrigation, the yield of oil was 231.2 kg/ha, which was 21% more than irrigation treatment. The results of interaction between sowing date and cultivar showed that the highest yield of seed oil (2576.6 kg/ha) was obtained on the 20th of September and L72 cultivars. The lowest values were obtained on the 5th of November and the HW3 cultivar. In general, the L72 had more seed oil yields on both dates. The results showed that the main effect of year, main effect of irrigation, main effect of cultivar, main effect of planting date and interaction effects of planting date on cultivar was significant on grain yield. In the second year, grain yield was more than the first year. In irrigation, grain yield was 4444.72 kg/ha, which was 30% more than irrigation treatment. The results of interaction between sowing date and cultivar showed that the highest grain yield was obtained at 4231.2 kg / ha in sowing date of 11th of October and L72 cultivar. The lowest values were obtained on the 26th of October and the HW3 cultivar. In general, the L72 had more seed yield on both dates.