Induction and Transformation of Friable Callus in Chrysanthemum ‘Jimba’

The friability of callus is closely associated with its genetic transformation efficiency, and optimizing induction and transformation conditions is essential for establishing an efficient transformation system. In this study, we developed a high-efficiency friable callus induction and Agrobacterium-mediated transformation system for Chrysanthemum ‘Jimba’. Three plant growth regulator (PGR) combinations—6-Benzylaminopurine (6-BA) + Naphthaleneacetic Acid (NAA), 6-BA + 2,4-Dichlorophenoxyacetic Acid (2,4-D), and Thidiazuron (TDZ) + 2,4-D—were evaluated for their effects on callus morphology, proliferation, and transformation efficiency. The optimal PGR combination was identified as 1.0 mg/L 6-BA + 0.4 mg/L NAA, which produced highly friable calli with a loose structure, rapid proliferation, and the highest nuclear-to-cytoplasmic ratio. The optimal subculture time for maintaining friability and high proliferation was the 7th week, while the best Agrobacterium infection conditions were OD600 = 0.5 with a 10 min infection period, which achieved a transformation efficiency of 91%. This optimized protocol provides an efficient and rapid transformation method for future gene function studies using callus transformation.