a two year experiment was carried out in a split plot design based on RCBD with four replications at the research field of Seed and Plant Improvement Institute, Karaj, Iran during 2002-2004 crop years with the objective to determine the drought stress tolerance of spring rapeseed (Brassica napus L.) varieties using drought stress tolerance indices (STI, MP and GMP) and identifying the most appropriate index for drought stress tolerance evaluation. Treatments were included Irrigation in two levels (I: I1: irrigation after 80 mm evaporation from the class A pan (normal irrigation,) and I2: no irrigation from stem elongation stage up to the end of growth (water stress) as main plots and varieties in 20 levels (V1: Sarigol, V2: Goliath, V3: Heros, V4: Comet, V5: Amica, V6: SW 5001, V7: Cracker Jack, V8: Eagle, V9: Wild cat, V10: SW Hot shot, V11: Ogla, V12: 19-H, V13: Hyola 401 (Canada), V14: Hyola 401 (Safi abad), V15: Hyola 401 (Borazjan), V16: Hyola 420, V17: Syn 3, V18: Option 500, V19: Hyola 308, V20: Quantum) as sub plots. The results of combined analysis indicated that no irrigation from stem elongation stage up to the end of growth decreased seed yield. Syn 3 variety produced the highest seed yield and STI under water stress condition among varieties, while under normal irrigation condition the highest seed yield obtained by Hyola 401 (Canada) variety. Quantum variety with the lowest seed yield under normal irrigation, low seed yield in water stress condition and the lowest STI was known as the most susceptible variety to drought stress. STI known as the most appropriate index for drought stress tolerance evaluation due to highest correlation with seed yield in both water and non water stress conditions.
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