Domesticated Barley (Hordeum vulgare L.) Originated from an Intermedium Type of Wild Barley

Barley (Hordeum vulgare L.) was domesticated from its wild two-rowed ancestor H. vulgare ssp. spontaneum (C. Koch.) Thell. To clarify the phylogenetic relationship between two- and six-rowed domesticated barley, and to better understand the role of the intermedium row-type during barley domestication history, phenotypic analyses and re-sequencing of three known row-type genes (six-rowed-spike 1 (Vrs1), Vrs4 and Intermedium –c, Int-c) was performed in a worldwide collection of Intermedium-barleys (302 accessions), wild barley ssp. spontaneum (100), ssp. agriocrithon (10) and H. bulbosum (3) accessions. Measuring lateral floret length and width revealed the presence of two distinct row-type groups within wild barley; one row-type form with enlarged but infertile lateral florets, designated here as ssp. spontaneum-Intermedium, and one group with significantly smaller lateral florets, similar to domesticated two-rowed barleys, designated here as ssp. spontaneum-Distichon. 93.7% of the Intermedium-barley collection, all ssp. spontaneum-Intermedium and H. bulbosum carried the two-rowed allele Vrs1.b in combination with the six-rowed allele Int-c.a. Further network analyses revealed that ssp. spontaneum-Intermedium, phylogenetically closer to H. bulbosum, is the direct ancestor of ssp. spontaneum-Distichon and all domesticated barleys. All ssp. spontaneum-Distichon accessions, however, possessed only two-rowed alleles at both Vrs1 and Int-c; whereas ssp. agriocrithon carried six-rowed specific alleles at all tested loci. Vrs1 transcript levels in wild and Intermedium-barleys predominantly correlated negatively with lateral spikelet fertility as expected, indicating that Intermedium-barleys are a rich genetic resource for increasing lateral spikelet fertility in breeding programs. A revised model of barley evolution and domestication is discussed.