Genotypic and Phenotypic Analyses of Wild and Intermedium Barleys Highlights Two Distinct Row-Types in Hordeum spontaneum

Cultivated barley (Hordeum vulgare L.) was domesticated from its wild two-rowed ancestor H. vulgare ssp. spontaneum. The row-type of the barley inflorescence is controlled by at least six independent loci, including six-rowed-spike1 (vrs1), vrs2, vrs3, vrs4, intermedium-c (int-c) and labile (lab). To clarify the relationship between two-, six-rowed cultivated barley, and to better understand the importance and role of ‘Intermedium’ row-type during barley evolution and domestication, phenotypic analyses and re-sequencing of three known row-type genes (Vrs1, Vrs4 and Int-c) was performed in a large worldwide ‘Intermedium’ barley collection (302 accessions), wild barley ssp. spontaneum (100 acc.) and ssp. agriocrithon (10 acc.) accessions. Measuring lateral spikelet length and width revealed the presence of two distinct row-type groups within wild barley ssp. spontaneum; one ‘Intermedium’ row-type form with enlarged but infertile lateral spikelets, designated as ssp. spontaneum (Intermedium), and one group with significantly smaller lateral spikelets similar to cultivated two-rowed barleys, designated as ssp. spontaneum (Distichon). 93.7% of the ‘Intermedium’ barley accessions and all wild barley ssp. spontaneum (Intermedium) types carried alleles at vrs1 specific for two-rowed barley in combination with the six-rowed-specific allele of Int-c.a. All ssp. spontaneum (Distichon) accessions possessed two-rowed alleles at both the vrs1 and the int-c loci, respectively. On the contrary, six-rowed wild barley ssp. agriocrithon carried six-rowed specific alleles at all tested loci. These results provide new insights into the relationship between wild and cultivated barleys during domestication, and identify ‘Intermedium’ barleys as a rich genetic resource for increasing lateral spikelet fertility.