Shade Resistance of Maize Cultivars Released from the 1990s to the 2010s in the North China Plain

Low-light stress poses an increasing threat to maize yield, yet the changes in low-light adaptability of cultivars during breeding progress remain unclear. A two-year field experiment was conducted using maize cultivars released in the 1990s, 2000s, and 2010s, with 6-day shading imposed at the tasseling stage. Yield, dry matter allocation, silk growth, sugar metabolism enzyme activities, and endogenous hormones were analyzed to characterize changes in shade tolerance. Low-light stress reduced maize yield, but the yield reduction was lower in cultivars from the 2010s than in earlier cultivars. The reduction in kernel number per ear was closely related to the reduction in yield. Silk number showed a highly significant positive correlation with kernel number per ear. Compared with the control, the silk numbers of maize cultivars from the 1990s, 2000s, and 2010s decreased by 38.09%, 40.57%, and 26.62%, respectively. Furthermore, we found that the sugar content, related enzyme activities, and hormone content in the silks of cultivar from the 2010s were more stable. These findings provide a basis for improving shade tolerance and developing maize cultivars adapted to low-light environments.