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Effects of Population Density upon Agronomic Traits Associated with Genetic Increases in Yield of Zea mays L.¹

Several long term recurrent selection programs with strains of Zea mays L., which were initiated from one to three decades ago, are being carried out at plant densities considerably below those currently used in commercial production. The question arises whether responses realized at low plant densities will be maintained at higher plant densities. We chose to study strains from a selection program initiated three decades ago, in which 10 cycles of full-sib family selection have been completed at a density of 24,000 plants per hectare. A study was conducted to characterize changes in agronomic traits of corn resulting from recurrent selection for yield when evaluated at 24,710, 38,300, and 49,420 plants per hectare. Comparisons were made among the original strain and strains resulting from the fifth (C₆) and 10th (C₁₀) selection cycles.

The improved strains, C₅ and C₁₀, averaged 27 and 42% more yield than the original strain. Important increases in prolificacy, ear corn/stover ratio, and total N accumulation in the grain were found to accompany the increases in yield due to selection. Increased population density resulted in greater yields per hectare in the improved strains. Interactions between strain and density were not statistically significant.

Both ear height and top height increased with selection, but leaf size and ear weight appeared to have decreased. Decreases were also noted in percent N in the grain and the stover.

Key Words: Corn • Maize • Full-sib family section

² Professor, Dep. of Genetics, and professor, Dep. of Soil Science, North Carolina State Univ.

Received for publication December 12, 1975.

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