Effect of Drought Stress at Different Growth Stages on Seed Yield and some

Effects of drought stress through interruption of irrigation at different growth stages on seed yield and some agro-physiological traits of safflower were studied at Seed and Plant Improvement Institute, Karaj during 2002-2004 cropping seasons. The experiment design was a split plot that arranged in completely randomized block with three replications. Six interrupting irrigation treatments S1 (blooming and seed development), S2 (blooming and flowering), S3 (blooming), S4 (flowering), S5 (seed delopment) and S6 (control) were arranged in main plots and three spring safflower cultivars Isfahan local, Arak 2811 and FO2 in subplots. The results of combined analysis demonstrated that the differences among treatments were significant(P<0.01) for seed yield. The highest seed yield belonged to Isfahan local (1258 kgha-1) in non-stress condition, that was not significantly different from that of S5(seed developing) treatment (1159 kgha-1).The highest damage on seed yield caused by S2(blooming and flowering stress) indicated that blooming and flowering are two important stages in safflower growth period. The lowest damage was observed in S5(seed developing) treatment. It was concluded therefore that S5 stage could be a suitable stage for irrigation interruption in safflower cultivars. The crop growth rate (CGR) increased in different interrupting irrigation levels up to flowering stage and decreased afterward. The lowest amount of RGR observed at S2 stress treatment. Based on the results, interruption of irrigation at seed development stage has less effect on seed yield but can save irrigation water in safflower farms.