Investigation of water stress and planting date (atumn & spring) effect on á-tocopherol content in spring rapeseed cultivars.

In order to study water stress and planting date(atumn & winter), on á-tocopherol content of spring rapeseed cultivars; an experiment was carried out in a factoriel split plot design based on RCBD with three replications for two years in Karaj. Treatments were included: 1-Irrigation in two levels as main plots such as common irrigation and no irrigation from flowering to end of growth. 2- Planting dates in two levels as main plots such as atumn planting (15 Mehr) and winter planting (20 Esfand). 3- Varieties & Hybrids as sub plots in 10 levels including of RGS003, Sarigol , Hyola401, Hyola420, Hyola330, RGS006, RG4403, RG405/03, RGAS0324 and RG405/02. Tocophrrol fractions, á,ã and ä tocopherols were analysed with HPLC. The results showed simple effect of planting date, irrigation & variety and also interaction effect of planting date & variety, irrigation & variety and planting date & irrigation & variety on á-tocopherol content were significant at 1% level probability. But interaction effect of planting date & irrigation was not significant. Atumn planting had significant preference to winter planting at 5% level probability with means of 25.71 & 25.08 mg/kg seed, respectively. Also no irrigation from flowering to end of growth was better than common irrigation with means of 29.88 & 23.88 mg/kg seed, respectively. Atumn planting & no irrigation had significant preference to atumn planting & common irrigation, with means of 28.82 and 22.60 mg/kg seed, respectively. Finaly, Sarigol in atumn planting & no irrigation from flowering to end of growth with mean of 53.27 mg/kg seed and Hyola401 in atumn planting & common irrigation with mean of 14.46 mg/kg seed had the highest and the lowest content of á-tocopherol, respectively. Also, RG405/03 in atumn planting & common hrrigation, Sarigol in in atumn planting & no irrigation from flowering to end of growth, RGS003 in winter planting & common irrigation, RGS006 in winter planthng & no irrigation from flowering to end of growth had the highest content of á-tocopherol.