Exogenous GA3 improves wheat yield by increasing proximal grain weight

Wheat grain weight is determined by the contributions of both proximal and distal grains. To investigate whether exogenous hormones can enhance grain weight by differentially modulating assimilate distribution, we applied auxin (IAA), 6-benzylaminopurine (6-BA), gibberellic acid 3 (GA 3 ), abscisic acid (ABA), and ethylene to wheat at 1–4 d post-anthesis. Results indicated that only GA 3 significantly increased average grain weight (by 5.17–7.09%) and yield (by 8.66–9.15%) across two growing seasons. Exogenous GA 3 application increased proximal grain weight by 5.85–10.17% through accelerated filling rates and an extended duration during the gradual-growing phase. This improvement was driven by elevated endogenous GA 3 and IAA levels, as well as enhanced activities of sucrose synthase (SS) and ADP-glucose pyrophosphorylase (AGPase). Conversely, distal grain weight decreased by 5.05–7.22% under GA 3 treatment due to reduced filling rates during the same phase, and this decline was associated with increased levels of zeatin riboside (ZR), GA 3 , and IAA and suppressed SS and soluble starch synthase (SSS) activities. Under the field conditions of this study, exogenous GA 3 application notably boosted wheat yield by preferentially enhancing proximal grain filling. These findings suggest that prioritizing the enhancement of proximal grain weight via exogenous hormone regulation is a viable strategy for increasing average grain weight in wheat.