Effect of planting date and source - sink limitation on grain yield and yield components in three rapeseed (Brassica napus L.) cultivars

To study the effect of different planting dates and source-sink limitations on grain yield and its components in three rapeseed cultivars, a field experiment was conducted using split-factorial arrangements in randomized complete block design with three replications at Bayekola Research Station, Sari, Iran, in 2006 and 2007 cropping seasons. Planting dates; 22 October and 01 November were assigned to main plots and three rapeseedcultivars: Hayola 401, RGS 003 and Sarigol and source-sink limitations at five levels: removing 1/3 of leaves from lower, middle and upper parts of plant, removing 1/3 of flowers and control in factorial arrangement were randomized in sub-plots. Results showed that rapeseed cultivars had very significant (P<0.01) differences for allmeasured traits, except for grain number.silique-1 (P<0.05). Planting date had significant effect on plant height, grain yield, silique number.plant-1 and silique length. The first sowing date was more suitable than the second date for growing rapeseed cultivars. Hayola 401 and RGS 003 had the highest grain yield (2911 and 2808 kg.ha-1) in the second cropping season, and the highest grain yield (2988 kg.ha-1) at the first planting date was related to Hayola 401. The lowest grain yield was obtained from RGS 003 (974 kg.ha-1) in 2006 cropping season and, the second planting date (1556 kg.ha-1). All treatments - significantly (P<0.01) affected the silique number.plant-1. Furthermore, all traits except silique number.plant-1 (248.08 siliques in 2007) and 1000 grain weight (4.08 g in 2007), had greater scores in 2007 in comparison with the 2006 cropping season. It seems that source limitation might not be determining factor for mentioned rapeseed cultivars, because of better yield in cutting of one third lower leaves compared to control.