A Highly Efficient Protocol for Multiple In Vitro Somatic Shoot Organogenesis from the Hypocotyl- and Cotyledon-Derived Callus Tissues of Russian Cabbage Genotypes

Generation of state-of-the-art highly productive cabbage genotypes (Brassica oleracea convar. capitata (L.) Alef.) with improved agronomic traits is attainable using modern biotechnological approaches. However, capitata cabbage is relatively recalcitrant to de novo shoot organogenesis from callus tissue, especially with loss of somatic cell totipotency during genetic transformation. An effective and rapid protocol for in vitro indirect shoot organogenesis from hypocotyl and cotyledon explants derived from 6-day-old aseptic donor seedlings of Russian cabbage genotypes (the DH line as well as cvs. Podarok and Parus) has been developed. In order to obtain standardized donor explants, aseptic cabbage seeds were germinated under dim light conditions (30–40 µmol m⁻² s⁻¹) with a 16 h light/8 h dark photoperiod. Multiple indirect shoot organogenesis (1.47–4.93 shoots per explant) from both cotyledonary leaves and hypocotyl segments with a frequency of 55.2–89.1% was achieved through 45 days of culture on the 0.7% agar-solidified (w/v) Murashige and Skoog (MS) basal medium containing 2 mg/L 6-benzylaminopurine (6-BAP), 0.02 mg/L 1-naphthalene acetic acid (NAA), and 5 mg/L AgNO₃. The regenerants were successfully rooted on an MS basal medium (69.2%) without plant growth regulators (PGRs), as well as supplemented with 0.5 mg/L NAA (86.8%). Subsequently, in vitro rooted cabbage plantlets were adapted to soil conditions with an efficiency of 85%. This rapid protocol, allowing for the performance of a full cycle from in vitro seed germination to growing adapted plantlets under ex vitro conditions over 95 days, can be successfully applied to induce an indirect shoot formation in various cabbage genotypes, and it is recommended to produce transgenic plants with improved quality traits and productivity.