effects of drought stress in reproductive stages on photoassimilates partitioning of rapeseed (brassica napus)

partitioning of photoassimilates between the sinks is one of the most important physiological processes related to the yield of crops which are affected by drought stress. therefore, the effect of drought stress in flowering and grain filling stages, on the percentage partitioning of photoassimilates among different organs was studied in 14 rapeseed cultivars in a split plot experiment based on completely randomized block design with 3 replications. main plot included 3 regimes of irrigation and sub plot included 14 cultivars of rapeseed. drought stress was imposed at two stages of flowering and grain filling stages by stopping irrigation. in the former treatment plots were rewatered when soil water potential reached -1.5 mpa and in the latter plots were not ireirrigated until maturity. seed yield, dry weight per plant, percentage dry weight of pod, leaf, stem and root measured after ripening and harvest. the results showed that drought stress at flowering and grain filling stages play an important influence in the partitioning of photoassimilates among different plant organs so that the stress at flowering stage decreased seed yield by 51 percent through increasing dry weight percent of leaf, stem and root or in other words percentage partitioning of photoassimilates to growing organs were more than reproductive organs. drought stress in seed filling increased somewhat seed yield through remobilization of photoassimilates in leaves to other organs. however, this increase didn’t make significant changes on the yield. among the cultivars studied, opera, hayola308, hayola420, p.f and zarfam that before of flowering stage have high dry weight per plant and equal partitioning among organs, after ripening in normal condition have high seed yield by partitioning of photoassimilates to pods. in this study interaction of irrigation and cultivar on the partitioning of photoassimilates was not significant so that all cultivars with a similar process were affected by drought stress.