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Family Per Se Response to Selfing and Selection in Maize Based on Testcross Performance: A Simulation Study

MDS Harris, 621 Rose St., Lincoln, NE 68501
HybriTech Seed International, 806 North Second St., P.O. Box 1320, Berthoud, CO 80513
USDA-ARS and Dep. of Animal Sciences, Univ. of Nebraska-Lincoln, Lincoln, NE 68583
Dep. of Biometry, Univ. of Nebraska, Lincoln NE 68583
Pioneer Hi-Bred International, Inc., NW 62nd Ave., P.O. Box 85, Johnston, IA 50131

^* Corresponding author (blaine.e.johnson{at}monsanto.com).

Determining the appropriate number of lines to retain across generations during inbred line development in maize (Zea mays L.) is crucial for efficient allocation of resources. Although the primary interest during line development is performance of testcross progeny, genetic information on lines per se adds to basic understanding of the genetic response of maize to inbreeding and selection. The objective of this research was to compare genetic responses of families per se to varying selection intensities across early generations of selfing in maize. A FORTRAN program simulating a stochastic genetic model with 30, 40, and 30% additive, dominant, and over-dominant loci, respectively, and a random environmental effect was used to compare varying combinations of selection intensities across generations. In the simulation, individual plants were evaluated on the basis of testcross progeny performance using multiple testers and environments. Individual plants corresponding to top performing testcross progenies were selected as parents for successive generations. Within each generation, phenotypic and genetic means of families per se increased with increased selection intensities. Response to selection in any given generation was not dependent on selection intensity used in the previous generation. Percent homozygosity and frequency of superior alleles increased as selection pressure intensified. Few original plants contributed to retained families with only approximately 5% of S₀ plants appearing in pedigrees of selected S₄ families. Retaining few but larger families resulted in increased genetic values of families per se, compared with saving a large number of smaller families, even though selection was based on testcross performance.

Received for publication April 23, 1996.

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