affected seed yield when sunflower

affected seed yield when sunflower plants grown under the well-irrigated and extreme water deficit conditions (Table 5
and 7). While, seed weight was the main yield component determined seed yield when sunflower plants endured
moderate water stress (Table 6). The decrease of LAI in some filed crops exposed to water stress stage has been reported previously (Connor and Jones, 1985; Pandey et al., 2000; Mansouri-Far et al., 2010). It found that reducing radiation capture due to loss in LAI under water shortage conditions resulted in assimilation reduction (Shangguan et al., 2000: Saneoka et al., 2004). The previous studies showed that limited irrigation-water can significantly decrease sunflower seed yields (Stone et al., 1996), especially during three growth periods: heading, flowering, and milking stages
(Osman and Talha, 1975). A decrease in the number of seeds per head and seed weight after the irrigation deficit at
different growth periods was also reported (Göksoy et al., 2004; Beheshti and Behboodi fard, 2010). The number of
seeds per head is positively associated with seed yield in sunflower (Punia and Gill, 1994; Doddamani et al., 1997).
The results showed that the Euroflor and Allestar hybrids had the highest seed yield under full and limited irrigation
conditions, respectively (Table 4). The results of correlation analysis showed that a significant, high and negative
relationship between seed yield and LAI when sunflower plants grown under water irrigation deficit conditions (Table
6 and 7). The Allester hybrid with the less LAI had the highest seed yield when it was grown under water irrigation
deficit condition (Table 4). Thus, the hybrids with less LAI could be more benefit in water stress conditions. It was found that there was a diversity between cultivars to response drought stress, and these variations involve in resistant
reactions (Tollenaar and Lee, 2002; Casadebaig et al. 2008; Mansouri-Far et al., 2010). Among drought adaptation
strategies, the minimization of water loss can be achieved through the lowering of either leaf area, stomatal conductance
or a reduction of the energy load of the plant (Sadras et al., 1993; Rauf and Sadaqat, 2008). Casadebaig et al. (2008)
found that a robust relationship between leaf expansion or daily transpiration and available soil water content. Pandy et
al. (2000) found that reducing LAI to decrease transpiration and a deeper root system to increase water extraction are the
adaptive strategies in maize plant under water stress.