High frequency somatic embryogenesis and plant regeneration from papaya hypocotyl callus

Abstract

High frequency somatic embryogenesis in papaya (Carica papaya L.) tissue cultures was achieved by culturing hypocotyl sections from ten-day-old seedlings on half-strength Murashige and Skoog salts (MS) medium containing modified MS vitamins, 2.3 to 112.5 μM 2,4-dichlorophenoxyacetic acid (2,4-d), 400 mg l-1 glutamine, and 6% sucrose. Four hermaphroditic Hawaiian cultivars produced embryogenic calluses after ten to 14 weeks of culture at 27°C in the dark. Efficiency in embryogenic response of genotypes differed, ‘Kapoho’ > ‘Sunset’ > ‘Sunrise’ > ‘Waimanalo’. The frequency of embryogenesis in induction medium containing 4.5 μM 2,4-d was lowest with 3% sucrose and highest with 7% sucrose. Somatic embryos developed directly from embryogenic calluses on induction medium, or, more often, they differentiated from calluses subcultured on a medium devoid of growth regulators. Between 50 and 500 embryos were produced from each 2-mm hypocotyl section after at least two months on induction medium and two months on maturation medium. Embryos subsequently developed into normal-looking plants on MS medium. Shoot cuttings from germinated embryos and micropropagated plants were rooted with 5.0 μM indole-3-butyric acid (IBA), grown in the greenhouse, and transferred to the field.