Establishment of an efficient shoot regeneration system in vitro in Brassica rapa

To improve the genetic transformation system for Brassica rapa L., we established a high-efficiency shoot regeneration protocol. A double haploid line ‘CX001’ with strong regeneration ability was identified from among 25 genotypes. Cotyledons from 4-d-old ‘CX001’ exhibited high-frequency (77.14%) shoot regeneration when explants were cultured on Murashige and Skoog (MS) basal medium supplemented with 1.0 mg L−1 6-benzylaminopurine (BA) and 0.5 mg L−1 α-naphthaleneacetic acid (NAA). The highest regeneration frequency (85.40%) and the maximum shoots number per explant (1.79) were achieved on medium containing 2.0 mg L−1 BA and 0.5 mg L−1 NAA. The addition of 2.5 mg L−1 AgNO3 was critical to shoot regeneration of the cotyledonal explants. The highest rooting rate was obtained on MS medium supplemented with 0.1 mg L−1 NAA. Flow cytometric analysis indicated that there was no ploidy variation between the mother plant and the regenerated plants. Regenerated plantlets with healthy roots were domesticated and transplanted into pots under greenhouse conditions. A reliable and efficient shoot regeneration protocol was established, which lays the foundation for genetic transformation in Brassica rapa.