Morphological, physiological and biochemical trait analysis of maize inbreds under drought conditions

Maize (Zea mays L.) is a crucial cereal crop that is highly sensitive to drought, which disrupts its morphological, physiological and biochemical traits, impairing photoassimilate allocation. A 2-year field experiment was conducted to assess drought tolerance mechanisms in 6 maize inbred lines—CBM-DL 38, CBM-DL 111, CBM-DL 238, CBM-DL 448, CBM-DL 360 and UMI 1200—by evaluating morphological, physiological, biochemical changes as well as carbohydrate assimilation during sensitive growth stages. Drought stress was applied at different growth stages and observations were recorded 10 days after stress initiation. Drought stress significantly affected growth stages, canopy traits, carbon assimilation and yields. The chlorophyll index decreased by 17–23%, the vegetative index by 33–36% and chlorophyll fluorescence by 47–48%. Meanwhile, the leaf angle increased to 25–30° and the flagging point ratio was reduced to 0.8, resulting in 56–59% yield reduction. However, CBM-DL 38, CBM-DL 111, CBM-DL 448 and CBM-DL 360 demonstrated enhanced drought tolerance, with reduced malondialdehyde (1.5–1.8 times), increased proline (75–93%), improved antioxidant activities [catalase (52–76%), peroxidase (45–57%)] and higher leaf tissue water content (43–59%). Improved leaf architecture enhanced light captures and resource allocation, reducing oxidative damage and maintaining yields. In contrast, CBM-DL 238 and UMI 1200 showed greater reductions in cob weight and 100-grain weight (47–49%). Drought stress during 35–75 days after sowing (DAS) severely impaired photosynthesis, leading to reduced yields. Enhanced canopy traits and biochemical resilience made CBM-DL 38, CBM-DL 111, CBM-DL 448 and CBM-DL 360 more drought-tolerant.