Yield formation of wheat with different ear types under water-saving supplementary irrigation conditions

To investigate the effects of water-saving supplemental irrigation on photosynthesis, senescence, and grain filling characteristics of flag leaves in tillers of wheat varieties with different spike types, and to elucidate the physiological mechanisms underlying yield formation under supplemental irrigation, an experiment was conducted using two wheat varieties: the medium-spike Jimai 22 (J22) and the large-spike Shannong 23 (S23). Three irrigation regimes were applied: no irrigation throughout the growing season (W0); water-saving supplemental irrigation (W70), which maintained 70% relative soil moisture in the 0-40 cm layer at both the jointing and flowering stages; and full supplemental irrigation (W90), which maintained 90% relative soil moisture at the same stages and depth. A total of six treatment combinations were evaluated to compare photosynthetic performance senescence characteristics of flag leaves on tillers, and grain filling parameters between the two spike-type varieties. Results showed that under water-saving supplemental irrigation, S23 exhibited higher relative chlorophyll content, net photosynthetic rate, sucrose content, superoxide dismutase activity, and soluble protein content in the flag leaves of tillers after flowering, along with lower malondialdehyde content, compared with other treatments. Additionally, the average grain filling rate, maximum grain filling rate, and duration of the active grain filling period were significantly higher, contributing to a significantly greater grain weight. Under water-saving supplemental irrigation, the single-plant grain yield of S23 increased by 8.39% to 45.16%, and the grain yield per hectare increased by 5.76% to 44.32%, compared with other treatments. Although no significant yield difference was observed between the water-saving and fully irrigated S23 treatments, the total irrigation volume under water-saving irrigation was 14.82% to 52.61% lower, while irrigation water use efficiency was 22.33% to 122.74% higher, In conclusion, the water-saving supplemental irrigation treatment for S23 achieved higher grain yield and the highest irrigation efficiency by enhancing the accumulation of photosynthetic products in tillers and their branches, making it the most effective treatment under the experimental conditions.