Reduction of a Triticum monococcum chromosome segment carrying the softness genes Pina and Pinb translocated to bread wheat

Endosperm texture, i.e., the hardness or softness of the grain, is an important trait because it determines many end-use properties of wheat (Triticum aestivum L.). It is primarily controlled by the puroindoline genes (Pina and Pinb) at the Hardness (Ha) locus, mapped on the short arm of chromosome 5D. The introgression of functional Pin genes from diploid wheat Triticum monococcum L. chromosome 5A(m) into hexaploid wheat resulted in softer grains, suggesting that this translocation might be useful for soft wheat breeders. However, the translocated segment includes a large portion of the 5Am short arm and may carry detrimental genes for agronomic performance. In this study we have generated a backcross (BC) population of 210 individuals where 5A-5A(m) homeologous recombination was induced by the ph1b mutation to recover individuals with a reduced translocated segment. A map of this region was constructed using specific sequence tagged site (STS) markers for the three T monococcum Ha-related genes, the completely linked BGGP gene, three wheat ESTs (BG606847, BF474606, and BQ168958), and two microsatellite markers. Eight plants with recombination events between XBggp and the closest proximal locus BG606847 were identified. Of these, four have the desired T monococcum allele at the Ha locus. These plants carry a 6.3-cM segment of T monococcum chromatin proximal to the Ha locus. This germplasm, which will be publicly available, and the molecular markers developed in this study will be valuable tools for soft wheat breeding programs.