Low-nitrogen-tolerant maize hybrid can alleviate the effects of low light and low nitrogen stress on grain physical and starch quality

The physical properties and starch quality of maize grains are critical for industrial processing, yet the combined effects of low light and low nitrogen (N) on these traits in different positional grains of hybrids with varying low-N-tolerance remain unclear. This two-year field experiment compared the low-N-tolerant hybrid ZhengHong 311 (ZH311) and the low-N-sensitive hybrid XianYu 508 (XY508), under natural light (CS) and 35% shading (SS), combined with low N (150 kg ha −1 ) and normal N (240 kg ha −1 ). We evaluated the grain morphological characteristics, test weight and hardness, starch and protein contents and their fractions, and starch granule morphology and pasting properties. The results showed that low light and low N significantly reduced soluble sugars, starch and protein contents and their fractions (particularly soluble sugars, albumin, and globulin), leading to decrease the grain size, test weight, and hardness. Under low light and low N, starch granules became more irregular and porous, and the proportion of large granules increased, which raised starch peak viscosity (PV), trough viscosity (TV), and final viscosity (FV), especially in XY508. Overall, apical grains were more negatively affected by low light and low N, particularly in XY508, whereas ZH311 maintained relatively stable grain quality under combined stress. This study provides insights for breeding maize hybrids resilient to low N and low light, and for developing management strategies to mitigate the effects of combined low light and low N stress. • Low light and low N reduced maize grain physical and starch quality; • Low light exerted a greater effect on starch quality, while low N on protein content; • Low light and low N had greater effects on XY508 and on apical grains; • Starch granule size distribution is the primary factor influencing its pasting properties.