Selection for Early Flowering in Corn: Seven Late Synthetics

Seven corn ( Zea mays L.) synthetics adapted to southern Iowa were grown in southern Minnesota at high plant density, and the earliest 5% to flower were sibmated for five generations. The original populations and the five selected cycles were then compared in performance trials at three plant densities over 2 years. Selection effect per cycle averaged: 1.1 q/ha yield increase, 2.2 ears/100 p.lants increase (1‐year data), 1.6 percentage points grain moisture decrease, 2.8% stalk breakage increase, 6.1 cm plant height decrease, 4.1 cm ear height decrease, 1.7 days less to flower, and 0.4 days less silk delay. We observed a cycle‐by‐density interaction wherein advanced cycles exhibited prolificacy at a low density after selection against barrenness at high densities. The decrease in silk delay and increase in ears per plant indicate that selection for early flowering during stress is effective in adapting materials to high plant densities. Flowering date is highly heritable and responds readily to selection. Selection for early flowering is an effective way to adapt late corns to an earlier area. It provides more genetic divergence than the pedigree method or other breeding schemes that use early germplasm as donor of maturity genes. Strong correlated responses to selection for early flowering were found for lower kernel moisture, lower plant and ear height, and higher stalk breakage. Earlier flowering increased yields among late flowering corns and decreased yields among early ones. Earlier flowering increased yields in a short, cool season and decreased yields in a long, warm season. These phenomena can be explained by the contrasting relationships of flowering date with plant size and length of grain filling period: earlier flowering increases yield when longer grain filling period is critical and decreases yield when larger plant size is more important.