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Selection for Early Flowering in Corn: Three Adapted Synthetics

Res. and Development Dep. DeKalb-Pfizer Genetics, DeKalb, IL 60115

^* Corresponding author.

Corn (Zea mays L.) breeders strive to broaden genetic diversity within shorter-season growing areas by selecting for early flowering in late-maturity germplasm. This creates earlier flowering material with most of the characteristics of the late germplasm, thus broadening the diversity of germplasm grown in the shorter-season area. The present study evaluates selection for early flowering in adapted germplasm; relative to flowering date of selection materials, not only place of selection but also place of intended use differs from the usual approach. This study measures the selection response for early flowering in three adapted synthetics. The synthetics were grown at high plant density (87 000 plants ha^-1) near Mankato, MN; the earliest 5% to flower (55 of 1100 plants) were selected for four generations, then the original populations and the four cycles for each synthetic were compared in performance trials at 48 300,62 600 and 75 500 plants ha^-1 for 5 yr. Selection response for early flowering for four cycles averaged 0.8 d less to flowering, 10 g kg^-1 less grain moisture, 4.0 cm less plant height, 2.7 cm less ear height, 0.2 d less silk delay, 0.15 Mg ha-1 (3%) less yield, and 4% more broken stalks. The decrease in yield due to selection showed close association with decrease in plant size (r = 0.98**, significant at P = 0.01), which probably reduced photosynthetic capacity. Later-flowering synthetics respond more to selection for early flowering than do earlier flowering synthetics. Shorter-season growing areas with longer, cooler days at flowering favor selection for early flowering. The results indicate that selection for early flowering can help export new, diverse germplasm to shorter-season growing areas, to broaden genetic diversity in the shorter-season area.

Received for publication August 11, 1989.