An ancient super allele of the Vrs1 gene driving the recent success in modern barley improvement through optimising spike architecture

Improved yield potential is the goal of barley domestication and cultivation. During this process, two- and six-rowed barley types emerged and have been utilised in breeding and production. The six-rowed type could produce three times as many grains as its ancestral two-rowed forms, thus dominating barley cultivation for thousands of years. The deficiens form of the two-rowed type, characterised by extremely suppressed lateral spikelets, has gained dominance over the past few decades in barley-growing regions worldwide. We hypothesised that the absence of lateral spikelets in deficiens barley affects spike architecture and spike-related traits, contributing to its superior yield potential of deficiens barley cultivation. Currently, a deficiens barley variety, RGT Planet, is the most popular barley variety in the world. In this study, we used two F₂ populations derived from crossing RGT Planet with two canonical two-rowed barley and identified the functional allele Vrs1.t1 associated with deficiens morphology. We observed that the Vrs1.t1 allele may contribute to high yield potential by optimising spike architecture through increased spikelet length, grain number, and grain size. Phylogenetic analysis suggests that the deficiens mutation was likely present from the early stages of barley cultivation in the Fertile Crescent and spread to Ethiopia and beyond with agricultural expansion. We conclude that the ancient deficiens allele Vrs1.t1 has been a critical driver for the recent success of modern barley improvement by optimising spike architecture.