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

Authors: ELLI, ELVIS - Iowa State University; Edwards, Jode; YU, JIANMING - Iowa State University; TRIFUNOVIC, SLOBODAN - Bayer Cropscience; EUDY, DOUGLAS - Bayer Cropscience; KOSOLA, KEVIN - Bayer Cropscience; SCHNABLE, PATRICK - Iowa State University; LAMKEY, KENDALL - Iowa State University; ARCHONTOULIS, SOTIRIOS - Iowa State University

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2023
Publication Date: 9/29/2023
Citation: Elli, E.F., Edwards, J.W., Yu, J., Trifunovic, S., Eudy, D.M., Kosola, K.R., Schnable, P.S., Lamkey, K.R., Archontoulis, S.V. 2023. Maize leaf angle genetic gain is slowing down in the last decades. Crop Science. 63(6):3520-3533. https://doi.org/10.1002/csc2.21111.
DOI: https://doi.org/10.1002/csc2.21111

Interpretive Summary: Continued genetic improvement in crop cultivars will be needed to meet global grain demands and to adapt to changes in climate. In order to maintain genetic progress is elite maize cultivars, breeders need to understand what traits to target in order to maintain continued improvement. Changes in orientation of maize leaves were examined in maize hybrids representing modern hybrids and hybrids grown during the last 40 years. The orientation of leaves has become more vertical in hybrids developed over the 40 years. However, it was also apparent that leaf orientation is reaching a maximum (nearly vertical) which will limit future yield gains from improvements in this trait. The results indicate that other traits may become more important for future genetic gain. The results from this study will benefit breeders and scientists who developing new hybrids and improved breeding methods.

Technical 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. We measured leaf angle in 78 maize hybrids released between 1980 and 2020 across eight environments in the US Corn Belt. Our objectives were to (i) quantify leaf angle genetic gain per canopy position in Bayer's legacy hybrids; (ii) dissect the contribution of breeding from plant density on historical changes in leaf angle, and (iii) synthesize our findings with literature to determine leaf angle changes over a century of breeding. We found that new hybrids had on average 6° more erect leaves than old hybrids. The leaf angle genetic gain (towards more erect leaves) was on average 0.08% year-1 for the middle canopy leaves and 8-fold 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 towards 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 maize breeding has found alternative avenues to continue increasing grain yields. Our study provides prospects to inform breeders and crop modelers to better understand maize leaf architecture and crop yields.