Golden Promise-rapid, a fast-cycling and transformable barley genotype

The spring barley cultivar Golden Promise (GP) is the major reference genotype for transformation due to its high transformability and availability of a reference genome. However, GP is characterized by a long generation cycle and stress susceptibility under non-optimal growth conditions because it carries a mutation at the floral inducer Photoperiod-H1 (Ppd-H1). Previously, we showed that a GP introgression line, Golden Promise-fast (GP-fast), generated by introducing the wild-type Ppd-H1 allele from the winter barley cultivar Igri, exhibits early flowering and improved stress resilience. In this study, we generated a fast-cycling genotype, Golden Promise-rapid (GP-rapid), isogenic to GP with good regeneration capacity and transformability. We conducted two backcrosses of GP-fast to reduce the residual Igri genome. The resulting genotype contains only a single introgression of approximately 0.6 Mbp at the Ppd-H1 locus on chromosome 2H. Under speed breeding conditions, its generation time was reduced to 63 days (25% shorter than GP's 84 days). Parallel transformation of GP, GP-fast, and GP-rapid using CRISPR/Cas9-mediated genome editing of Ppd-H1 revealed that GP-rapid remains amenable to Agrobacterium-mediated transformation. Overall, we report on the development of a fast-cycling GP isogenic line as a research tool for efficient generation of transgenic and gene-edited barley plants.