Time-course of genotype and hormone-related effects on callus proliferation in barley genetic transformation

Successful barley genetic transformation is dependent on genotype selection, which largely limits its molecular breeding. To elucidate the effects of genotype and hormone on callus induction and differentiation of barley, we investigated the growth performance of callus proliferation and differentiation of green spot in three Chinese cultivars (ZU9, ZU10 and Hua30), one Australian malting barley (Franklin) and one Scotland Whisky barley (Golden Promise). The three Chinese barley showed shorter spikes but larger immature embryos after flowering for 15 ​d than the other two genotypes. Golden Promise had the largest callus proliferation and green spot differentiation than the other genotypes. Meanwhile, ZU10 showed a relatively similar appearance and high efficiency to Golden Promise, which highlights its capacity for genetic modification. Golden Promise maintained relatively higher expression of hormone-related genes at almost all stages of callus proliferation, including auxin and cytokinin related HvPIN1, HvARF3, HvRR6 and HvWOX11, which may explain its higher efficiency in genetic transformation. Adjusting hormone concentration to 1 ​mg ​L⁻¹ 6-BA and 0.25 ​mg. L⁻¹ 2,4-D in transition medium significantly increased green spot differentiation for most genotypes. These findings may provide useful information for overcoming genotype dependency with optimal hormones at callus proliferation stages of barley.