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Divergent Mass Selection for Ear Length in Maize¹

Mass selection for increased and decreased ear length was conducted in ‘Iowa Long Ear Synthetic’ of maize (Zea mays L.) for 10 generations. Evaluation trials of the selected populations were conducted in five environments, and measurements were made for ear length and eight other plant and ear traits. The objectives of the study were to determine the direct and correlated responses for 10 cycles of divergent mass selection for ear length in Iowa Long Ear Synthetic.

Direct response to 10 cycles of divergent mass selection for ear length was asymmetrical. The predicted and realized responses for increased ear length were nearly the same. Realized response for decreased ear length, however, was twice as great as for increased ear length. It seemed that unequal gene frequencies and directional dominance of genes affecting ear length were responsible for the asymmetry observed for ear length.

The correlated responses of grain yield per plant, ear diameter, kernel depth, ear height, and days to silking also were asymmetrical. Selection response for increased ear length was not accompanied by a correlated response in grain yield per plant. Selection response for decreased ear length, however, was accompanied by a significant response for decreased grain yield per plant. A significant decrease in kernel depth with selection for increased ear length caused the lack of yield response with selection for increased ear length. Other correlated responses to selection for increased ear length were taller plants, later silking, and decreased diameter. Selection for decreased ear length resulted in shorter plants, but there was no change in days to flower, ear diameter, and kernel depth. Selection for increased ear length was not effective for increasing yield.

Key Words: Zea mays L. • Breeding methods • Direct selection • Indirect selection • Correlated responses

² Maize and sorghum breeder, Satilla, Mexico; and research geneticist, AR, SEA, USDA, and professor of plant breeding, Iowa State Univ., Ames, IA 50011.

Received for publication August 25, 1978.

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