Submitted to: Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/13/2005
Publication Date: 10/25/2005
Citation: Gu, X.-Y., Kianian, S.F., Foley, M.E. 2005. Phenotypic selection for dormancy introduced a set of adaptive haplotypes from weedy into cultivated rice. Genetics. 171:695-704. Interpretive Summary: Seed dormancy is a key characteristic of weedy plants. In the course of our research to develop weedy rice as a system to map-base clone dormancy quantitative trait loci (QTL), we developed advanced generation backcross populations. Using different generation of backcross and two BC4F2 populations we verified several dormancy QTLs and chromosomal regions that contain both a dormancy QTL and QTLs/genes for interrelated weedy traits. We propose that seed dormancy genes shelter haplotypes, i.e., a group of tightly linked alleles that tend to be inherited together, that facilitate adaptation of weeds.
Technical Abstract: Association of seed dormancy with some other adaptive traits enhances the survival of wild and weedy species, but challenges the use of dormancy genes in breeding varieties for resistance to preharvest sprouting. A selection and recurrent backcrossing technique was used to introduce dormancy genes from a wild-like weedy rice to a breeding line to determine their effects on germinability and linkage with undesirable traits. Five generations of single plant selection for low germination extremes simultaneously retained five dormancy QTL regions, including qSD12 (R2 > 50%), based on their main and/or epistatic effects in two BC4F2 populations. Four dormancy loci with moderate to small effects co-located with QTLs/genes for one to three of the traits awn length, shattering, black hull color, and red pericarp color. Multi-locus response to the selection suggests that these dormancy genes are cumulative in effect, as well as networked by epistases, and that the network may have played a sheltering role in maintaining the intact adaptive haplotypes during the evolution of weeds. The tight linkage may prevent dormancy genes in haplotypes from being used in breeding programs. The major effect of qSD12 consisted of a predominant gene additive effect, which makes it an ideal target for map-based cloning and the best candidate for imparting resistance to preharvest sprouting.