quantifying factors determining seed weight in open pollinated and hybrid oilseed rape (brassica napus l.) cultivars

seed weight (sw) in oilseed rape (brassica napus l.) is determined during the seed filling period (sfp). a great proportion of variation in sw is associated with environmental conditions in this period. to quantify factors determining sw in open pollinated (op) and hybrid cultivars of oilseed rape, 12 field experiments were conducted at agricultural research station of gonbad, iran, during 2000-07 growing seasons. the experiments were often carried out under optimal growing conditions. results clearly showed the importance of air temperature in determining the duration of the sfp, and consequently sw. the sw was maximized for the cultivars when exposed to the lower temperatures during the sfp. the ability of cultivars to produce photosynthetic assimilates for developing seeds was an effective determinant factor for sw. the relationships between sw with leaf area index (lai) and aboveground dry matter, (adm) at the onset of sfp, was positive and strong, showing a greater response of hybrid cultivars to increase in lai and adm as compared to ops. in both groups, temperature and radiation interactions during sfp, as showed by photo-thermal quotient (ptq), reasonably explained variation in sw. therefore, further increase in seed yield (sy) through increasing sw could be obtained by improvement in one or a combination of these environmental factors as well as crop characteristics. these relationships are simple tools that could be applied to simulation models of sw in oilseed rape.