Allelic Variants at the Psy-A1 and Psy-B1 Loci in Durum Wheat and Their Associations with Grain Yellowness

Phytoene synthase (PSY) genes are involved in the biosynthesis of carotenoid pigments in durum wheat [Triticum turgidum L. subsp. durum (Desf.) Husn.], significantly influencing grain yellowness. This study was conducted to identify new allelic variants at the Psy-A1 and Psy-B1 loci in durum wheat, and to evaluate the applicability of functional markers developed from common wheat (Triticum aestivum L.) for durum wheat breeding. Two new allelic variants, Psy-A1d and Psy-A1e, were identified at the Psy-A1 locus, and both the codominant markers YP7A and YP7A-2 can be used to discriminate the two haplotypes, yielding 194- and 231-bp polymerase chain reaction (PCR) products with YP7A and 1001- and 1684-bp fragments with YP7A-2, respectively. At the Psy-B1 locus, three allelic variants were identified. Psy-B1e was also found in common wheat, whereas Psy-B1f and Psy-B1g were detected only in durum wheat. The codominant marker YP7B-1 can be used to distinguish Psy-B1f and Psy-B1g, generating 151- and 153-bp PCR fragments, respectively, and the dominant marker YP7B-4 was specific to haplotype Psy-B1e, producing a 717-bp PCR product. In a set of 100 CIMMYT durum wheat lines with widely variable grain yellowness, the frequencies of Psy-A1d, Psy-A1e, Psy-B1e, Psy-B1f, and Psy-B1g were 99, 1, 0, 67, and 33%, respectively, and the genotype Psy-B1f showed a significant association with higher grain yellowness, whereas the presence of Psy-B1g led to lower yellowness. A phylogenetic tree generated from the gene sequences of the allelic variants at Psy-A1 and Psy-B1 loci indicated two parallel lineages of durum-common wheat, suggesting that more than one tetraploid T. turgidum L. subsp. dicoccon (Schrank) Thell. genotypes were involved in the origin of common wheat. Our results suggested that Psy-B1f should be paid more attention in durum breeding programs for its association with elevated grain yellowness.