Selection Response in Subdivided Target Regions
- G. N. Atlin *a,
- R. J. Bakerb,
- K. B. McRaec and
- X. Lud
- a Dep. of Plant Science, Nova Scotia Agricultural College, P.O. Box 550, Truro, NS, B2N 5E3 Canada
b Dep. of Plant Sciences, Univ. of Saskatchewan, Saskatoon, SK, S7N 0W0 Canada
c Atlantic Food and Horticulture Research Centre, Agric. and Agri-Food Canada, 32 Main Street, Kentville, NS, B4N 1J5 Canada
d SCPFRC, Agric. and Agri-Food Canada, 43 McGilvray St., Univ. of Guelph, Guelph, ON N1G 2W1 Canada
In a small target region, it may be possible to exploit local adaptation to increase gains from selection. However, in a large region more extensive testing is usually possible, resulting in more precise estimation of genotype means. A correlated response model was adapted to determine if division of a large target region is likely to increase gains. Genotypic value in a large region and constituent subregions are considered correlated traits. Correlated response in a subregion to indirect selection across the undivided region, relative to direct response to selection within the subregion, is expressed as a function of heritability in the undivided region (H) and in the subregion (Hi ), and of the genotypic correlation between region and subregion means (rG′ ). rG′ depends on the magnitude of the genotype × subregion interaction (σ2 GS) relative to the genotypic variance (σ2 G). σ2 GS is the portion of the genotype × location interaction (σ2 GL) caused by local adaptation, rather than by random site-to-site variability in genotype means. Subdivision can increase heritability through the addition of σ2 GS to the numerator of Hi , but this may be offset by reduced replication across locations within the subregion. Modeling using variance estimates from several cereal programs indicated that, unless σ2 GL is large relative to σ2 G and at least 30% of σ2 GL is due to σ2 GS, subdivision is unlikely to increase response. These results help explain the success of breeding programs that test broadly.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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