Regulating female ear morphogenesis in maize by uniconazole and 5-aminolevulinic acid for yield improvement

Female ear development during the pre- and post-silking period is critical for maize yield. Although plant growth regulators can enhance yield, their specific effects on ear morphogenesis and underlying mechanisms are not fully understood. In this study, two maize hybrids were foliar-treated with uniconazole (UCZ, 25 mg L⁻¹) or 5-aminolevulinic acid (ALA, 40 mg L⁻¹) at the 12-leaf stage. UCZ and ALA increased grain yield by 6.8% to 12.0% and 8.3% to 13.9%, respectively. This yield improvement resulted not only from increased 100-grain weight but, more importantly, from a greater kernel number per ear achieved through enhanced row number (by UCZ) and grains per row (by ALA). Morphological analysis revealed that UCZ significantly increased ear diameter, whereas ALA markedly promoted ear elongation. Physiologically, UCZ lowered IAA and GA levels but raised ABA, while ALA exerted opposite effects on these hormones. Both regulators enhanced ZR and carbohydrate contents. In conclusion, UCZ and ALA enhance maize yield through distinct pathways: UCZ favors radial growth and yield components related to ear thickness, whereas ALA promotes longitudinal growth and components related to ear length.