Establishment of a High-Efficiency In Vitro Regeneration and Agrobacterium-Mediated Genetic Transformation System for Ajania achilleoides (Turcz.) Poljakov

Ajania achilleoides, a wild species with strong environmental adaptability, is a valuable germplasm resource for genetic improvement and functional gene studies. However, efficient in vitro regeneration and genetic transformation systems for this species remain undeveloped, limiting functional gene characterization and genetic improvement of this valuable germplasm resource. In this study, leaf explants were used to establish an efficient regeneration system by evaluating different combinations of plant growth regulators and to develop an Agrobacterium tumefaciens-mediated genetic transformation system for A. achilleoides. MS medium supplemented with 2.0 mg/L 6-benzyladenine (6-BA) and 1.0 mg/L α-naphthaleneacetic acid (NAA) achieved the highest adventitious shoot regeneration rate (99%), while 1/2 MS medium containing 0.5 mg/L indole-3-butyric acid (IBA) was optimal for rooting, resulting in a 100% rooting rate. Critical hygromycin concentrations for shoot regeneration and rooting selection were determined to be 25 mg/L and 10 mg/L, respectively. For transformation, the best results were obtained with a 3-day preculture, bacterial suspension at OD600 = 0.2, 30 min infection, and 2-day co-cultivation. PCR and sequencing confirmed the successful integration of the target genes into the genome, yielding three positive transgenic lines with a molecular confirmation rate of 30%. This study establishes a stable and efficient regeneration and transformation system for A. achilleoides, providing a platform for functional gene analysis and molecular breeding of wild chrysanthemum species.