A novel mutation conferring the nonbrittle phenotype of cultivated barley

The nonbrittle rachis, resulting in a seed head which does not shatter at maturity, is one of the key phenotypes that distinguishes domesticated barley from its wild relatives. The phenotype is associated with two loci, Btr1 and Btr2, with all domesticated barleys thought to have either a 1 bp deletion in Btr1 or an 11 bp deletion in Btr2. We used a PCR genotyping method with 380 domesticated barley landraces to identify those with the Btr1 deletion and those with the Btr2 deletion. We discovered two landraces, from Serbia and Greece, that had neither deletion. Instead these landraces possess a novel point mutation in Btr1, changing a leucine to a proline in the protein product. We confirmed that plants carrying this mutation have the nonbrittle phenotype and identified wild haplotypes from the Gaziantep region of southeast Turkey as the closest wild relatives of these two landraces. The presence of a third mutation conferring the nonbrittle phenotype of domesticated barley shows that the origin of this trait is more complex than previously thought, and is consistent with recent models that view the transition to agriculture in southwest Asia as a protracted and multiregional process.