Association of phytoene synthase Psy1-A1 and Psy1-B1 allelic variants with semolina yellowness in durum wheat (Triticum turgidum L. var. durum)

Phytoene synthase (Psy) is a key gene influencing semolina yellowness. Specific molecular markers have been developed to identify some of the known allelic variants of Psy1-A1 (Psy1-A1a, Psy1-A1l, Psy1-A1o) and Psy1-B1 (Psy1-B1a, Psy1-B1b) associated to semolina yellow color. This study was undertaken to assess the genetic variability existing for Psy1, and to evaluate the relationship between genotype and phenotype, in two contrasting durum wheat panels formed mostly by American breeding lines (BL panel), and a collection that included 155 Mediterranean landraces and 20 modern cultivars (M panel). The BL panel showed h(2) values over 0.93 for two indicators of yellowness [i.e. semolina yellow pigments absorbance, and b* values that were strongly correlated (r = 0.95, P<0.0001)], reflecting the strong genetic control of semolina yellowness. Compared to the BL panel, the M panel showed greater variability in Psy1-A1 and Psy1-B1 allelic frequencies, but only Psy1-A1 exhibited significant differences in yellowness. This suggests that using molecular markers associated with Psy1-A1 (i.e., Psy1-A1_STS and YP7A-2 jointly) for marker assisted selection can be sufficient and valuable to improve grain yellowness. The presence of the Psy1-A1l allele was associated with the highest values of semolina yellowness, whereas the presence of the Psy1-A1a allele was associated with the lowest values for this trait in the M panel. Fourteen genotypes carrying high-yellowness Psy1 allelic variants were identified in both the BL and the M panels. These can be used as parents for increasing yellowness in durum breeding programs.