| To investigate the physiological response mechanism of different degrees of water stress on the development of superior and inferior grains in maize, a 2-year continuous pond planting maize experiment was conducted under controlled conditions. Two maize varieties with differences in drought tolerance were selected as experimental materials, and a total of six treatments were set up, including T1 (drought tolerant variety - no stress), T2 (drought tolerant variety - moderate water stress), T3 (drought tolerant variety - severe water stress), T4 (drought sensitive variety - no stress), T5 (drought sensitive variety - moderate water stress), and T6 (drought sensitive variety - severe water stress). Study the changes in grain filling characteristics, starch synthesis, hormone content, and yield of superior and inferior grains of maize under different degrees of water stress. The research results indicate that water stress significantly affects the filling process of superior and inferior grains in maize. The filling rate of inferior grains in drought sensitive maize varieties during the late filling stage (45 d, 55 d) and the decrease in 100-grain weight during each sampling period were higher than those in drought resistant maize varieties. The filling rate under moderate and severe water stress decreased by an average of 30.73% and 35.36%, respectively. The decrease in maximum grain filling rate (Gmax) and average grain filling rate (Vmean) of inferior grains was higher than that of drought resistant maize varieties. Among them, under moderate and severe water stress, the Gmax decreased by an average of 24.97% and 39.68%, and the Vmean decreased by 23.54% and 36.70%, respectively. Water stress can significantly affect the starch content, acid sucrose invertase, starch synthase, sucrose synthase, and ADPG pyrophosphorylase activities, as well as the content of auxin, cytokinin, and abscisic acid in superior and inferior grains of maize. The drought sensitive maize variety has the highest degree of change in inferior grains. Compared with untreated maize varieties, drought sensitive maize varieties showed a higher decrease in yield, ear length, ear diameter, and number of grains per ear. Among them, maize yield decreased by an average of 9.83% and 18.57% under moderate and severe water stress, and the decrease in 100 grains weight of inferior grains during maturity was higher. Under moderate and severe water stress, the average decrease was 23.51% and 36.34%. In summary, water stress has a significant impact on the final yield formation of maize by affecting the starch synthesis and filling of inferior grains, and severe water stress has a more significant impact on it. The research results can provide theoretical basis and reference for maize production and drought resistant maize variety selection in semi-arid areas. |