An improved plant regeneration protocol for a popular Indian Madhubindu variety of papaya (Carica papaya L.) via somatic embryogenesis

Papaya (Carica papaya L.) is an important fruit crop, and it is highly nutritive and has several medicinal properties. In the present study, we have developed an improved protocol for in vitro plant regeneration through somatic embryogenesis. A  high seed germination rate was achieved, when the seeds were treated with 600 ppm of gibberellic acid to break the seed dormancy. Different explants, such as leaves, roots, hypocotyls, and mature zygotic embryos were inoculated on M1I2 medium supplemented with half-strength MS salts with full-strength vitamins, 400 mg/l glutamine, 100 mg/l proline, 160 mg/l adenine sulphate, 6% sucrose, 0.8% agar, and 4 mg/l 2,4-D for the induction of the embryogenic callus and further different stages of somatic embryos. Late torpedo and early cotyledonary stage SEs were regularly harvested and cultured on hormone-free MS medium in the dark till the roots appeared, and then transferred to light for further growth. For acclimatization, regenerated plants were transferred into earthen pots covered with polythene bags to maintain high humidity, grown for 2 months, and then transferred to greenhouse and then to the field conditions for their establishment.