Historical trends in maize morphology from the 1950s to the 2010s in China

The morphology of the plant and ear is a preliminary selection characteristic in breeding new varieties of maize. As new maize cultivars were developed from the 1950s through the 2010s in China, most had changes in both plant and ear morphological characteristics that contributed substantially to maize yield gains. Over the seven decades, plant and ear height fluctuated with a small increase from the 1950s to 2000s, and then a decrease in the 2010s, while the ear ratio and internodes length below the ear decreased significantly. Leaf angles became significantly more upright, especially for the leaves above the ear, and the leaf area per plant improved markedly. Leaf orientation increased from the 1950s to the 2000s then decreased in the 2010s. Tassel size and the anthesis–silking interval were both reduced substantially.Ear diameter, kernel number, and kernel weight increased from the 1950 to the 2000s, then decreased in the 2010s under the same cultivation conditions. We found that modern maize hybrids have a lower plant height, ear height and ear ratio which increased lodging resistance, a more erect leaf which increased high-density planting tolerance, and smaller ears and kernels which facilitated rapid dehydration during late grain filling. These morphological selection criteria, which are suitable for mechanized operations, are proposed as the focus for future maize breeding.