تاثیر منفی تنش خشکی بر عملکرد گلرنگ از طریق کاهش سطح فتوسنتزکننده و کارایی کوانتومی فتوسیستم ii

drought is considered as the most important constraint to world’s crop production. furthermore arid and semiarid climate accounts for nearly most of terrestrial areas of iran. therefore in order to study the effect of irrigation regimes on growth, physiological attributes and grain yield as well as components of such a crop plant as safflower 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 (i1), 105 mm (i2) and 135mm (i3) evaporation from a standard class a pan served as main plots, while six safflower genotypes including arak2811, kooseh, nebraska-10, c111, s149 and k12 constituted the subplots. chlorophyll fluorescence parameters (f0, fm and fv/fm) at heading and at pollination, leaf area index (lai) at %50 flowering, head/plant, seed/head, 1000 seed weight, grain and biological yield, oil content and harvest index were the traits assessed. lai differed among irrigation levels and genotypes, amounting to 5.05 and 2.33 for i1 and i3 levels of irrigation and 4.42 and 2.99 for s149 and nebraska, respectively. among chlorophyll fluorescence parameters, fv/fm decreased under i3 level of irrigation at both stages. grain yield decreased with drought, i1 outyielding i3 by 39%, due apparently to a greater seed/head (26%), head/plant (33%) and 1000 seed weight (10%) in the i1 as compared to i3 irrigation level. among grain yield components, head/plant and 1000 seed weight indicated the highest (0.86**) and the lowest (0.62**) correlation with safflower grain yield. irrigation level affected biological yield, with 37.18 and 24.65 g/plant for i1 and i3 respectively. it could be concluded that with genotypes employed in this experiment and the environmental conditions in 2007 in isfahan, drought negatively affects grain yield and it’s attributes due apparently to decrease in photosynthetic quantum efficiency and photosynthetic surfaces in safflower. chlorophyll fluorescence parameters proved useful in studying photosynthetic activity of safflower under drought stress.