Wheat is one of the most widely grown crops in the world. One of the traits that define wheat quality is grain hardness, which determines the amount of damaged starch generated during milling and, therefore, the end-use quality of a cultivar. Wheat grains can be classified into three main classes based on hardness (very hard or durum, hard and soft), with a wide range of values in between. Grain hardness is determined by puroindolines (PINA and PINB), proteins encoded by Pina-D1 and Pinb-D1 genes. In this study, the diversity of Pina-D1 and Pinb-D1 genes was evaluated in a collection of 300 Iranian common wheat landraces whose kernels had previously been classified as hard or semi-hard based on PSI analysis.

Four alleles previously described associated to hard grain were detected in the collection: Pina-D1 null in one accession, Pinb-D1b in eleven accessions, Pinb-d1ab in 183 accessions and Pinb-d1p in 80 accessions. In addition, a new allele was detected in Pinb-D1 at position 419 (G→A) that caused a change from cysteine to tyrosine at position 140 of the deduced protein. We named tentatively the novel allele Pinb-d1ak. This mutation is found in the tenth cysteine of the cysteine backbone of the protein, which is a highly conserved region. Accessions having the Pinb-d1ak allele showed in average a lower PSI value than the accessions having other Pin allele. This means that this novel allele may be associated with harder grains than other Pin alleles and could be used by breeding programs targeting different grain hardness levels. This study highlights the importance of conserving and characterizing wheat genetic resources that could be used as sources of genetic variability in breeding programs.