Agronomic Evaluation of Wheat (Triticum aestivum L.) Under Different Degrees of Drought–Rehydration Conditions Under Drip Irrigation

Establishing an optimal population structure is the fundamental approach to achieving high crop yield. By studying the changes in spring wheat yield and population structure under varying degrees of drought–rehydration conditions under drip irrigation, we can understand the balance between growth and stress response, explore the potential of wheat for biological water saving, and provide scientific evidence for the efficient production of drip-irrigated wheat in drought-prone areas. In this study, we used “Xinchun 6” (water-insensitive variety, XC 6) and “Xinchun 22” (water-sensitive variety, XC 22) as materials. Under two-year field planting conditions, mild (T1, J1, 60~65% FC, FC represents field capacity) and moderate (T2, J2, 45~50% FC) drought stress treatments were applied during the tillering and jointing stages, followed by drip irrigation for rehydration. The conventional drip irrigation served as the control (CK, 75~80% FC). We analyzed the relationship between the population quality and yield of different genotypes of wheat under water stress during the growth period and clarified the response of dry matter translocation to grains and high-quality populations to drought–rehydration. The results showed that drought stress reduced the tiller number (NT), leaf area index (LAI), grain number–leaf ratio (GNL), grain weight–leaf ratio (GWL), and dry matter weight. After rehydration, LAI, specific leaf weight (SLW), GNL, GWL, dry matter of vegetative organ and grain weight, and grain yield all reached their maximum values under T1 treatment. Compared with CK and moderate drought treatments (T2 and J2, respectively), these indicators under T1 treatment increased by an average of 1.04~30.96%, 0.82~6.28%, 0.57~26.10%, 0.41~8.01%, 0.48~41.10%, 0.53~13.97%, and 0.17~49.75%, respectively. Additionally, T1 treatment improved the post-flowering dry matter translocation rate and contribution rate. The compensatory effects on NT, LAI, GNL, GWL, and yield under drought–rehydration treatments during the tillering stage (T1 and T2) were superior to those during the jointing stage (J1 and J2). Correlation and path analysis indicated that yield was significantly positively correlated with LAI, GNL, and GWL, and increasing LAI had the best effect on yield increase. This suggests that rehydration after mild drought stress (T1) during the tillering stage can maintain a suitable leaf area for the population, enhance the grain–leaf ratio, promote post-anthesis material production and storage material transportation, coordinate the source–sink relationship, and achieve high yields for drip-irrigated spring wheat.