Identification of QTL and association of a phytoene synthase gene with endosperm colour in durum wheat

The yellow colour of durum wheat (Triticum turgidum L. var durum) semolina is due in part to the presence of carotenoid pigments found in the endosperm and is an important end-use quality trait. We hypothesized that variation in the genes coding for phytoene synthase (Psy), a critical enzyme in carotenoid biosynthesis, may partially explain the phenotypic variation in endosperm colour observed among durum cultivars. Using rice sequence information, primers were designed to PCR clone and sequence the Psy genes from Kofa (high colour) and W9262-260D3 (medium colour) durum cultivars. Sequencing confirmed the presence of four Psy genes in each parent, corresponding to a two member gene family designated as Psy1-1, Psy1-2 and Psy2-1 and Psy2-2. A genetic map was constructed using 155 F-1-derived doubled haploid lines from the cross W9262-260D3/Kofa with 194 simple sequence repeat and DArT (R) markers. Using Psy1-1 and Psy2-1 allele-specific markers and chromosome mapping, the Psy1 and Psy2 genes were located to the group 7 and 5 chromosomes, respectively. Four quantitative trait loci (QTL) underlying phenotypic variation in endosperm colour were identified on chromosomes 2A, 4B, 6B, and 7B. The Psy1-1 locus co-segregated with the 7B QTL, demonstrating an association of this gene with phenotypic variation for endosperm colour. This work is the first report of mapping Psy genes and supports the role of Psy1-1 in elevated levels of endosperm colour in durum wheat. This gene is a target for the further development of a molecular marker to enhance selection for endosperm colour in durum wheat breeding programs.