N6-benzyladenine (BAP)-Based Seed Preconditioning Enhances the Shoot Regeneration of Seedling-Derived Explants for Subsequent Indirect Gene Transfer in Soybeans (Glycine max [L.] Merrill.)

This study evaluated the effects of N6-benzyladenine (BAP) seed preconditioning and seedling-derived explants on in vitro plant regeneration potential in soybeans (Glycine max [L.] Merrill.). The findings showed that seed preconditioning with 2.55 mg/L BAP prior to germination significantly influenced seedling establishment and the development of shoots, shoot elongation, and rooting on MS media supplemented with BAP and TDZ, compared to the negative (MS-NC) and positive (MS-NP) controls. The results also showed significant differences based on the genotypes, with Dundee recording 91.0% germination over a minimum of 5 days, compared to 74.2% with Peking, followed by 87.5% and 80.0% overall shoot induction frequency in these genotypes, respectively. Regenerated shoots were successfully elongated on MS medium supplemented with 0.5 mg/L BAP plus 0.6 mg/L GA3 and rooted on hormone-free medium, for 3‒4 weeks, and then hardened in the acclimatization growth room under elevated light levels. Overall, this study revealed that BAP preconditioning of seeds enhances the frequency of bud initiation and shoot proliferation, mostly in whole-seedling and cotyledonary node explants subcultured on MS-E and MS-A media supplemented with BAP in combination with TDZ.