Drougt is the most important single constraint to world’s crop production and arid and semiarid climate accounts for nearly 96.7 percent of terrestrial areas of Iran . Therefore studying the effect of irrigatin regimes on growth, physiological attributes and grain yield and components of crop plants such as safflower is important. A 4-replicate split plot RCBD field study was performed at Lavark Reasrch Farm, Isfahan University of Technology, Isfahan , Iran in 2007. Three Irrigation levels, including irrigation after 75 mm (I 1 ), 105 mm (I 2 ) and 135mm (I 3 ) evaporation from a Standard Arak 2811, Kooseh, Nebraska-10, C 111 , S 149 and K 12 was considered as subplots. Chlorophyll fluorescence parameters ( F 0 , F M and F V /F M ) at heading and pollination, leaf earea index (LAI) at %50 flowering, head/plant, seed/head, 1000seed weght, grain and biological yield, oil content and oil yield and harvest index were measured. LAI differed among irrigation leveles and genotypes, amounting to 5.05 and 2.33 with I 1 and I 3 levels of irrigation and 4.42 and 2.99 for S 149 and Nebraska , respectively. Among chlorophyll fluorescence parameters, F V /F M decreased under I 3 level of irrigation at both stages. Grain yield decreased with drought, I 1 outyielding I 3 by %39, due apparently to a greater seed/head (%26) , head/plant (%33) and 1000seed weight (%10) in the I 1 compared to I 3 irrigation level. Oil yield was affected by irrigation level, resulting in 699.35 and 367.07 kgha -1 for I 1 and I 3 respectively. Among grain yield components, head/plant and 1000seed weight indicated the greatest (0.86 ** )and smallest (0.62 ** ) corrolation with safflower grain yield. Irrigation level affected biological yield, with 37.18 and 24.65 gr/plant for I 1 and I 3 respectively. it coud be concluded that with genotypes used in this experiment and the environmental conditions in 2007 in Isfahan, drougth negatively affects on grain yield and it’s attributes and photosynthetic quantum efficiency in safflower.
