Molecular and Cytogenetic Characterization of the 5DS-5BS Chromosome Translocation Conditioning Soft Kernel Texture in Durum Wheat

The durum wheat (Triticum turgidum ssp. durum (Desf.) Husn.) cultivar Soft Svevo with a soft kernel texture was developed through a Ph1b-mediated homoeologous 5DS-5BS chromosomal translocation. The soft kernel trait (Hardness locus) derived from chromosome 5D of the common wheat (Triticum aestivum L.) cultivar Chinese Spring. Soft Svevo was used as the donor parent to create near-isogenic soft durum germplasm. The size of the translocation, its estimated breakpoint, and the amount of chromosome 5BS translocated, if any, remain unknown. Four near-isogenic pairs of hard and soft kernel durum genotypes, in addition to Soft Svevo and the Chinese Spring deletion line 5DS-2, which lacks a distal 22% terminal segment of chromosome 5DS, were genotyped using Illumina's 90k wheat single nucleotide polymorphism array. Single nucleotide polymorphism results were processed in GenomeStudio and 164 polymorphic markers were identified between the near-isogenic lines (NILs). Subsequent BLASTn results for two subsets of markers corresponding to the distal ends of chromosomes 5DS and 5BS indicated that the translocation event was nearly reciprocal, as a similar to 24.36-Mbp segment of chromosome 5DS was gained, whereas a similar to 20.01-Mbp segment of chromosome 5BS was lost. Genomic in situ hybridization images of the soft durum NILs agreed with these estimates and confirmed the absence of additional terminal or interstitial translocations. Soft durum represents the potential of a new wheat market class and these findings will assist durum wheat breeders in the development of new soft durum germplasm.