Seed Yield Response of Rapeseed Genotypes to Delayed Sowing under Karaj Environmental Conditions

To investigate the effect of delayed sowing on seed and oil yields of rapeseed (Brassica napus L.) genotypes, a field experiment was carried out at the research field station of Seed and Plant Improvement Institute, Karaj, Iran in 2015-2016 and 2016-2017 cropping seasons. The experimental design was split plot arrangements in randomized complete block design with three replications. Optimal sowing dates (02 October) and delayed sowing date (01 November) were assigned to the main plots, and 17 rapeseed genotypes [French (eight), Iranian (five), Hungarian (two) and German (two)] were randomized in sub-plots. Combined analysis of variance showed that all main and interactions effects were significant on all studied traits (except the main effect of year on seed oil content). Plant developmental stages experienced different environmental conditions due to delayed sowing and led to decreases in seed yield and yield components, seed oil yield and biological yield. The highest seed yield in optimal sowing date belonged to Garou (in the first year) and HL2012 (in the second year) genotypes with an average of 5240 and 5805 kg ha-1, respectively. However, Okapi (in the first year) and Garou (in the second year) had the lowest seed yield in delayed sowing date with an average of 3624 and 2702 kg ha-1, respectively. Lauren (in the first year) and Darko genotypes (in the second year) had the lowest grain yield reduction (%) in delayed sowing date which accounted for 21.5% and 35.9%, respectively.