Study the effects of planting date and low irrigation stress on quantitative traits of spring sunflower (Helianthus annuus L.).

Water stress is a major limiting factor for sunflower production in the arid and semi arid regions in the world. In order to study the effects of sowing date and limited irrigation stress on plant height, head diameter, seed number per head, thousand seed weight, seed yield, biologic yield and harvest index of spring sunflower cultivar (Mehr), an experiment was conducted using a split plot arrangement based on randomised complete block design with three replications in Karaj, Iran, during 2008 and 2009.The present study showed that optimal environmental conditions around reproductive stages, provided by early sowing not only enhanced plant growth but also produced higher yield compared with those of late sowing dates. The April 20 th and May 9 th sowing produced larger seed yield, biologic yield and harvest index with no water stress treatment compared to late May sowing date with limited irrigation stress at stem elongation, flowering and grain filling stages respectively. The results showed that the limited irrigation stress resulted in reduction of seed yield due to limited vegetative and reproductive development. It is of prior concern to consider optimum sowing date so that high temperature of late sowing would not coincide with the reproductive stages of sunflower.