Selection for Lower Ear Placement in Two Synthetic Populations of Maize 1

Selection for lower ear placement in corn ( Zea mays L.) was done to obtain synthetics with a high plant to ear height ratio, to maintain maturities at or near the original materials, and to obtain additional information on whether selection for lower ear placement would reduce the number and length of internodes below the ear. An early and a late flowering synthetic was selected for lower ear placement by sib‐mating over a 10‐generation period; then the 10 cycles were compared in performance trials. Ear height was reduced from 67 to 41 cm in 10 cycles of selection in the early synthetic, or an average decrease of 4.3% per cycle. In the late synthetic, the reduction was from 69 to 51 cm, or an average decrease of 2.9% per cycle. Plant heights remained fairly constant in both synthetics. Plant to ear height ratios increased from 2.7 to 4.2 in the early synthetic and from 2.7 to 3.7 in the late synthetic. In both synthetics one less leaf was produced below the ear and one leaf added above the ear, while the total number of leaves remained fairly constant. Average internode lengths below the ear were reduced from 10.1 to 7.3 cm in the early synthetic and from 9.0 to 7.7 cm in the late synthetic after 10 generations. The effect of selection for lower ears was therefore shorter internodes and the ears being borne at a lower node. There was no change in number of days to silking in the early synthetic but there was a 2‐day delay in the late synthetic. Slightly higher grain moistures were obtained in the later cycles of both synthetics. Grain yield decreased in successive cycles of selection with correlations of 0.97 and .87 (both significant at the 0.01 level) between ear height and yield in the early and late synthetics, respectively. Stalk lodging was generally reduced as ear height was lowered but correlations were not significant. Uses of the synthetics in breeding programs are discussed.