The introduction history of Hordeum vulgare var. nudum (naked barley) into Fennoscandia

Abstract Hordeum vulgare var. nudum (naked barley) is one of the oldest and most common cereals found from Neolithic Fennoscandia. After the Bronze Age, naked barley largely disappeared and was replaced by Hordeum vulgare var. vulgare (hulled barley) and other cereals. During the early 19th century, naked barley of Asian origins was reintroduced to Fennoscandia. In this study, we have genetically characterized samples of Fennoscandian landraces of naked barley which were preserved in gene banks and museum collections. The analyses show that the Fennoscandian naked barley can be split into three groups: First, naked two-row barley, with a likely origin in Asia; second, naked six-row barley, with a likely origin in the eastern Himalayas and introduced during the 19th century; third, naked six-row barley genetically related to the original Fennoscandian hulled barley. The results suggest that this last group represents the ancient form of naked barley, which was possibly introduced in the Neolithic. At that time both naked and hulled barleys were grown and enough gene flow probably occurred between these two subspecies to create a Fennoscandian barley that is genetically distinct, irrespective of whether it is hulled or naked. This hypothesis was further supported by genotyping of the Nud gene, which is responsible for the naked phenotype. All naked barleys which we studied contained the same mutation allele, nud1.a , thus showing that naked Fennoscandian barley arose by crossings between naked and hulled barley and not by new mutations of hulled barley.