Maize leaf angle genetic gain is slowing down in the last decades

Abstract Quantifying historical changes in maize leaf angle and factors affecting it can enhance our understanding of canopy architecture and light capture, and hence crop productivity. Our objectives were to (1) quantify leaf angle genetic gain per canopy position in Bayer's legacy maize ( Zea mays L.) hybrids; (2) dissect the contribution of breeding from plant density on historical changes in leaf angle; and (3) synthesize our findings with literature to determine leaf angle changes over a century of breeding. We measured leaf angle in 78 maize hybrids released between 1980 and 2020 across eight environments in the US Corn Belt. We found that new hybrids had on average 6° more erect leaves than old hybrids. The leaf angle genetic gain (toward more erect leaves) was on average 0.08% year −1 for the middle canopy leaves and eightfold larger for the flag leaf. Our results revealed a synergistic effect with similar contributions of maize breeding and plant density on historical leaf angle changes in the middle canopy. However, changes in the bottom and top canopy leaves were due to breeding. Our results, combined with literature, revealed consistent trends toward more vertical leaves over a century of maize breeding, but the leaf angle genetic gain is slowing down in the last decades. This suggests that leaf angle may have reached near‐optimum levels and that multiple ways to maintain the grain yield genetic gain have been functioning in maize breeding. Our study provides prospects to inform breeders and crop modelers to better understand maize leaf architecture and crop yields.