Investigation of the effect of water deficit stress on yield and yield components in sunflower hybrids

In order to study the effect of water deficit stress on seed yield, yield component and some quantitative characteristics of sunflower hybrids, under three irrigation regimes (irrigation after 50 [normal irrigation], 100 [mild stress] and 150 [intense stress] mm cumulative evaporation from evaporation pan class A) and four sunflower hybrids (Azargol, Alstar, Hysun 33 and Hysun 25), an experimental split plot design based on a RCB was conducted in 2009 in the research station of university of Tehran, college of Abouraihan in Pakdasht region, Iran. Water stress significantly decreased seed yield, yield components and seed oil content but increased seed protein content in all sunflower hybrids. The highest seed yield of 2591 kg/ha was obtained from normal irrigation. An increase of the seed protein content and a decrease of the seed oil content occurred when water input decreased, although at different level for each hybrid according to their genetic constitution. Allstar hybrid had highest amount of all characteristics, except of seed oil and protein content. Results indicated that under normal irrigation, mild and intense water deficit stress, maximum seed yield was obtained by Azargol (3448 kg/ha), Alstar (2121 kg/ha) and Alstar (829 kg/ha) respectively. Therefore, Alstar hybrid under both levels of water deficit stress conditions in aspect of seed yield and related traits such as seed number per head, 1000 seed weight and head diameter had the most tolerance to these conditions. However, with normal irrigation, Azargol hybrid had highest seed yield.   Key words: Seed oil content, seed yield, sunflower, water deficit stress, yield component.