Abstract: 【Objective】This study investigated the effects of supplemental irrigation based on soil moisture measurement on flag leaf chlorophyll fluorescence and senescence characteristics in two wheat cultivars. 【Method】Under field conditions, the experiments were conducted in the growth seasons of 2013-2015 using the cultivars Jimai 22 (J22) and Tainong 18 (T18). Three treatments were applied, namely, no-irrigation during whole growth season (W0); an average relative soil water content of 65% in 0-40 cm soil layers at jointing and anthesis, respectively, by supplemental irrigation based on measured soil moisture (W1); and irrigation with 60 mm each at jointing and anthesis (W2, local supplemental irrigation practice). 【Result】W1 regulated the amount of irrigation at jointing and anthesis, maintained the relative water content of soil by 65% after irrigation, and prevented excessive or too low irrigation to create suitable soil moisture environment for wheat growth and development. On the 14, 21, and 28 day after anthesis, the electron transport rate, photochemical quenching of chlorophyll fluorescence, actual photochemical efficiency, and sucrose content of flag leaves were significantly higher under W1 than those under W2. The activity of sucrose phosphate synthase in flag leaves of W1 on 14 and 21 day after anthesis was significantly higher than that of W2. On the 14, 21, and 28 day after anthesis, the activities of superoxide dismutase and catalase in flag leaves in W1 were significantly higher than those in W2 for two cultivars. In addition, the MDA content in flag leaves was significantly lower than that of W2, and a high level of soluble protein content was maintained in flag leaves. During the two growing seasons, the grain yield, water use efficiency, and irrigation efficiency of W1 treatment for T18 and J22 were significantly higher than that of W2. Comparison among cultivars, on the 21, and 28 day after anthesis, the electron transport rate, photochemical quenching of chlorophyll fluorescence, actual photochemical efficiency, and sucrose content of flag leaves were significantly higher of T18 under W1 and W2 than those of J22. The activity of sucrose phosphate synthase in flag leaves of T18 on the 7, 14 and 21 day after anthesis was significantly higher than that of J22. On the 21, and 28 day after anthesis, the activities of superoxide dismutase and catalase in flag leaves of T18 were significantly higher than those of J22 in W1 and W2. In addition, the MDA content in flag leaves of T18 was significantly lower than that of J22, and a high level of soluble protein content was maintained in flag leaves. In the same growing season under the same treatment, no significant difference in total water consumption and water use efficiency was observed between T18 and J22. Grain yield and irrigation efficiency of T18 in W1 and W2 treatments were significantly higher than those of J22. However, the yield of T18 in W0 was significantly lower than that of J22. 【Conclusion】Supplemental irrigation based on soil moisture measurement (W1) could regulate the relative water content in soil to the targeted level at jointing and anthesis. W1 was suitable for two wheat varieties and effective in achieving both high yield and saving water. Under irrigation conditions, the yield potential of T18 was higher than that of J22. Under drought conditions, however, the sensitivity to moisture and yield of T18 were lower than those of J22.

Key words: wheat, soil relative water content, chlorophyll fluorescence, flag senescence, yield