UC Davis

The Hardness (Ha) locus on chromosome 5D is the main determinant of grain texture in hexaploid wheat (Triticum aestivum L.). Puroindoline (Pina-D1, Pinb-D1) and Grain Softness Protein (Gsp-D1) genes are tightly linked at this locus. Additional copies of the Gsp-1 gene are present on chromosomes 5A and 5B. Mutations in the Pina-D1 and Pinb-D1 genes have been individually associated with grain hardness, but it is not known if mutations at both loci may further increase hardness or if additional copies may reduce it. In addition, there is no clear evidence of the effect of the Gsp-1 genes on grain texture. To answer these questions, we compared the effect of different dosages of puroindoline and Gsp-1 genes on grain texture. Isogenic substitution and deletion lines for homoeologous group 5 in 'Chinese Spring' (CS) were evaluated in two replicated field trials with 13 blocks each. Deletions or allelic variants of Gsp-A1 and Gsp-B1 did not produce significant effects on grain texture, suggesting that these genes do not have a critical role in grain hardness. Simultaneous deletions of Pina-D1 and Pinb-D1 in deletion line 5DS-2 and substitution line CS (Red Egyptian 5D) resulted in significantly higher hardness index values than all other lines including CS (Timstein 5D) carrying a single Pina-D1 deletion (P = 0.02). The incorporation of additional copies of Pina-Am1 and Pinb-Am1 from T. monococcum L. in recombinant substitution line 5A/5Am in CS resulted in significantly softer grains than those from the CS control (P < 0.01).