ABSTRACT

To a large extent, the market value of wheat varieties is determined by the grain color. Pigmentation of wheat grain and coleoptile is controlled by the R gene on chromosomes of the homoeologous group 3 and the Rc gene on chromosomes of the homoeologous group 7, respectively. Each of these genes is inherited monogenically. Grain pigment has been suggested to be a derivative of catechin-tannin and that of coleoptile to be anthocyanin. These polyphenol compounds are known to be synthesized through the fl avonoid biosynthesis pathway. Himi et al. (2005) synthesized four partial nucleotide sequences of the early fl avonoid biosynthesis genes (CHS, CHI, F3H, and DFR) in wheat. Expression of these genes was examined in the

developing grains of red-grained and white-grained wheat lines wich were highly upregulated in the grain coat tissue of the red-grained lines, whereas there was no signifi cant expression in the white-grained lines. These results indicate that the R gene is involved in activation of the early fl avonoid biosynthesis genes. As for coleoptile pigmentation, all four genes were expressed in the red coleoptile; however, DFR was not activated in the white coleoptile. The Rc gene appears to be involved in DFR expression. Further, Breseghello and Sorrells (2006) performed association mapping on a selected sample of 95 cultivars of soft winter wheat and considered two other important grain qualities; grain size and milling characters. Consistent linkage disequilibrium on chromosome 2D was <1 cM, whereas in the centromeric region of 5A, linkage disequilibrium extended for approximately 5 cM. Association of 62 SSR loci on chromosomes 2D, 5A, and 5B with kernel morphology and milling quality was analyzed through a mixed-effects model, where subpopulation was considered as a random factor and the marker tested was considered as a fi xed factor. Permutations were used to adjust the threshold of signifi cance for multiple testing within chromosomes. Signifi cant markers for kernel size were detected on the three chromosomes tested, and alleles potentially useful for selection were identifi ed. Results demonstrate that association mapping could complement and enhance previous QTL information for marker-assisted selection.