An efficient embryogenic callus induction and plant regeneration system in Paeonia rockii

Paeonia rockii is valued for its ornamental and oil uses, yet its in vitro regeneration remains challenging due to low embryogenic callus (EC) induction, high browning, and the lack of a reported whole-plant regeneration system via callus. This study established an efficient callus regeneration system using zygotic embryos of the P. rockii ‘Yu Shi Zi’ as explants. The results showed that the callus originated from the cambium and parenchyma cells. The light yellow, loose-textured callus in the form of cell clusters or granules was identified as EC. The optimal EC induction medium was modified MS + 500 mg/L CH + 1.5 mg/L CPPU + 1.0 mg/L 2,4-D + 1.0 g/L CA + 30 g/L sucrose + 7 g/L agar, with the EC induction rate of 83.12% and the browning rate controlled at 21.50%. When cultured on a differentiation medium (modified WPM + 0.5 mg/L CPPU + 0.5 mg/L TDZ), the EC exhibited an adventitious shoot differentiation rate of 27.03% after 40 days. In addition, shoots of 1–3 cm in length were then subjected to a two-step rooting procedure, achieving a rooting rate of 18.7%. To the best of our knowledge, this report describes, for the first time, the establishment of a complete callus regeneration system in P. rockii , and successfully achieves plant regeneration.