In order to study the effect of irrigation regimes on growth, photosynthesis, leaf proline content and grain yield of safflower, a 4-replicate split plot RCBD field experiment was performed at Lavark Reasrch Farm, Isfahan University of Technology, Isfahan, Iran in 2007. Two Irrigation levels, including irrigating after 80 mm (I 1 =control) and 140 mm (I 2 =drought) evaporation from a Standard Net photosynthetic rate differed among irrigation levels and genotypes. At both heading and flowering stages drought decreased net photosynthetic rate by 51 and 56 % at heading and flowering, respectively. While the net photosynthetic rate was maximum in Kuseh, it was minimum in S 149 and C 111 at both heading and flowering stages. Moisture deficit in safflower increased leaf proline content by %83, averaged over genotypes, though the leaf proline level was not positively correlated to the grain yield. Maximum and minimum proline accumulations were observed in Kuseh and S 149 , respectively. LAI differed among irrigation levels and genotypes. Drought decreased LAI by 27.56%. A greater seed/head (%2.21), head/plant (%35.68) and seed weight (%12.34) was observed in I 1 , compared to the I 2 irrigation level. Grain yield decreased with drought, I 1 out yielding I 2 by %46. Oil yield and biological yield per plant and per hectare were decreased by irrigation level. Both grain yield and biological yield were positively correlated with photosynthetic rate at flowering and heading. It could be concluded that with genotypes used in this experiment and the environmental conditions in 2007 in Isfahan, drought negatively affects both photosynthetic rate and LAI in safflower, resulting in significant decreases in grain and biological yield. An increased level of leaf proline content under drought is an indicative of the stress level, rather than the resistance of this oil seed crop to the later environmental constrain. Key word: Safflower, photosynthetic rate, proline, grain yield, biological yield .
