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CROP BREEDING & GENETICS

Application of Population Genetic Theory and Simulation Models to Efficiently Pyramid Multiple Genes via Marker-Assisted Selection

^a Crop Research Informatics Lab., and Genetic Resources Enhancement Unit, International Maize and Wheat Improvement Center (CIMMYT), Apdo. Postal 6-641, 06600 Mexico, D.F., Mexico
^b CSIRO Plant Industry, 306 Carmody Rd, St. Lucia, QLD 4067, Australia
^c CSIRO Plant Industry, P.O. Box 1600, Canberra, ACT 2601, Australia
^d Institute of Crop Science, and The National Key Facility for Crop Gene Resources and Genetic Improvement, Chinese Academy of Agricultural Sciences, Beijing 100081, China

^* Correspondence author (wangjk{at}caas.net.cn or j.k.wang{at}cgiar.org).

Breeders face many complex choices in the design of efficient crossing and selection strategies aimed at combining desired alleles into a single target genotype. Both population genetic theory and a breeding simulation tool were used to study the effects of different strategies on population size and number of marker assays required to recover a target genotype in wheat (Triticum aestivum L.). Enriching the frequency of desirable alleles in the F₂ of single-cross and in the F₁ of backcross and topcross populations greatly reduced the minimum required population size, but the gain from another enrichment selection is minor. General equations were developed to determine appropriate crossing strategies, and sequential culling was proposed to minimize total marker screening costs. For a topcross of three adapted lines from an existing breeding program, simulation of changes in allele frequencies at nine target genes (seven unlinked) showed that population size was minimized with a three-stage selection strategy in the F₁ generation of the topcross (TCF₁), the F₂ generation of the topcross (TCF₂), and doubled haploid lines (DHs). Enrichment of allelic frequencies in TCF₂ reduced the total number of lines screened from >3500 to <600. Eight of the genes were present at frequencies >0.97 after selection, while the tin reduced-tillering allele was only at 0.77 in the final selected population due to its strong repulsion-phase linkage to the grain quality gene Glu-A3 in this cross and the incomplete linkage of the tin marker. Therefore, the presence of the tin gene needs to be further confirmed by other methods.

Abbreviations: DHs, doubled haploid lines • MAS, marker-assisted selection • QTL, quantitative trait locus or loci • RIL, recombination inbred lines • TCF₁, F₁ generation of the topcross • TCF₂, F₂ generation of the topcross

This article has been cited by other articles:

				Y. Xu and J. H. Crouch Marker-Assisted Selection in Plant Breeding: From Publications to Practice Crop Sci., March 19, 2008; 48(2): 391 - 407. [Abstract] [Full Text] [PDF]