Academic journal article Genetics

Fine Mapping and Marker Development for the Crossability Gene SKr on Chromosome 5BS of Hexaploid Wheat (Triticum Aestivum L.)

Academic journal article Genetics

Fine Mapping and Marker Development for the Crossability Gene SKr on Chromosome 5BS of Hexaploid Wheat (Triticum Aestivum L.)

Article excerpt

ABSTRACT

Most elite wheat varieties cannot be crossed with related species thereby restricting greatly the germplasm that can be used for alien introgression in breeding programs. Inhibition to crossability is controlled genetically and a number of QTL have been identified to date, including the major gene Kr1 on 5BL and SKr, a strong QTL affecting crossability between wheat and rye on chromosome 5BS. In this study, we used a recombinant SSD population originating from a cross between the poorly crossable cultivar Courtot (Ct) and the crossable line MP98 to characterize the major dominant effect of SKr and map the gene at the distal end of the chromosome near the 5B homeologous GSP locus. Colinearity with barley and rice was used to saturate the SKr region with new markers and establish orthologous relationships with a 54-kb region on rice chromosome 12. In total, five markers were mapped within a genetic interval of 0.3 cM and 400 kb of BAC contigs were established on both sides of the gene to lay the foundation for map-based cloning of SKr. Two SSR markers completely linked to SKr were used to evaluate a collection of crossable wheat progenies originating from primary triticale breeding programs. The results confirm the major effect of SKr on crossability and the usefulness of the two markers for the efficient introgression of crossability in elite wheat varieties.

DURING domestication and selection of a number of important crop species, diversity has eroded resulting in increased vulnerability to biotic and abiotic stresses while also jeopardizing the potential for sustained genetic improvement of elite cultivars over the long term (Tanksley and McCouch 1997; Fu and Somers 2009). The reintroduction of the remarkable diversity present in the different gene pools into elite varieties through intra- and interspecific crosses (primary and secondary gene pools) and intergeneric crosses (tertiary gene pools) has been practiced for decades in cereals (Feuillet et al. 2008). Despite some highly significant successes, including the incorporation of dwarfing and disease-resistance genes that fueled the Green Revolution, introgression remains laborious and, for complex characters, largely unfulfilled. Wheat (Triticum aestivum L.) has been crossed with a wide range of related species from the Triticeae tribe (Jiang et al. 1994), such as Aegilops, Agropyron, Haynaldia, Secale, and Hordeum, which represent a reservoir of interesting alleles for improving wheat resistance to biotic (diseases, insects) and abiotic stresses (cold, salinity, and drought) as well as for quality traits such as grain protein content (Fedak 1985). Intergeneric crosses have resulted in the transfer of desirable rye (Secale cereale L.) characteristics into wheat (Florell 1931) with one of the best examples being the 1BL/1RS chromosomal translocation that provided novel race-specific resistance to rust diseases, improved adaptation and stress tolerance, superior aerial biomass, and higher kernel weight to wheat varieties (Zarco-Hernandez et al. 2005). However, most of the adapted wheat germplasm is not crossable with alien species thereby restricting the panel of lines that can be used for alien introgression in wheat breeding (Krolow 1970) or for the production of primary triticale, a man-made wheat-rye hybrid.

Beginning in the early 1900s, researchers were producing experimental crosses between bread wheat, T. aestivum L. (2n¼6x¼ 42) as a recipient, and rye, S. cereale L. (2n ¼14) as the pollen donor (Backhouse 1916). Genetic studies conducted by Lein (1943) showed that dominant alleles of two genes, named Kr1 and Kr2 are responsible for the poor crossability between bread wheat and rye. Kr1 and Kr2 genes were localized roughly on chromosome 5B and 5A, respectively (Riley and Chapman 1967) and subsequently locatedmore precisely on the long arms of these two chromosomes (Lange and Riley 1973; Sitch et al. 1985). Further studies indicated that the dominant alleles driving incompatibility of crossing wheat with rye act by actively inhibiting the production of intergeneric hybrids (Riley and Chapman 1967; Lange and Wojciechowska 1976; Jalani and Moss 1980, 1981; Cameron and Reger 1991). …

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