Alterations in plant architecture and physiology allow maize to sustain yield after early defoliation

Abstract Maize ( Zea mays L.) tolerance to early defoliation is shaped by genotype‐specific physiological and morphological responses. Defoliation disrupts the source–sink balance, altering carbon allocation and plant development. Understanding these responses is crucial for optimizing breeding programs and agronomic management. In this study, the effects of complete canopy defoliation at vegetative stage 4 on growth parameters, root morphology, chlorophyll fluorescence, and yield stability in four maize genotypes were evaluated. Defoliation significantly reduced total leaf area, plant height, and root biomass while increasing root tissue density and the harvest index across all genotypes. Despite these structural changes, no significant differences were observed in key yield components, especially grain yield. Chlorophyll fluorescence analysis revealed distinct genotype‐specific responses. Under defoliation, KWS9606 VIP3 exhibited enhanced photochemical efficiency at 9 days after defoliation (DAD) and increased quenching photochemical (qP) at 17 and 24 DAD. While BRS1010, qP increased under defoliation at all dates, suggesting greater openness of PSII reaction centers. NPQ responses were variable and lacked a consistent pattern, indicating diverse energy dissipation strategies. NS90 PRO2 exhibited no significant differences between genotype × defoliation level combinations, reflecting limited physiological response. Principal component analysis highlighted the trade‐offs between morphological and physiological adaptations, with root traits dominating first principal component and chlorophyll fluorescence parameters influencing second principal component. These findings indicate that maize genotypes exhibit diverse acclimation mechanisms to mitigate defoliation stress while maintaining yield stability. Understanding genotype‐specific responses supports breeding programs aimed at improving tolerance to foliar loss and informs more resilient crop management strategies.