Effect of drought stress on photosynthesis characteristics in flag leaf of wheat cultivars in different years in the central Shaanxi plain

Winter wheat cultivars which have been popularized with large area in the central Shaanxi plain in recent 70 years were used as materials to study the effect of post-anthesis drought stress on photosynthesis characteristics in flag leaf.The results indicated that the drought resistance was increased with the replacement of wheat cultivars,under drought stress the yield of the wheat cultivars Wuzhi and Bima 1 which were the wheat cultivars before 1950 s was decreased by 18.2% and 38.3% compared with that under optimal water condition,but the yield of Xiaoyan 22 after 1990s was only decreased by 2.3%.The rate of photosynthesis and transpiration,stomatal conductance,single leaf water use efficiency in flag leaf under drought stress all decreased except the Ci which showed increasing trend before harvesting,the Gs in flag leaf of Bima 1 and Xiaoyan 22 averagely decreased by 5% and 18% on each stage after anthesis,but the Ci increased by 9% and 8%,which showed that the decrease of Pn in flag leaf was not caused by the decrease of Gs under drought stress.