Production of triploid plants of papaya by endosperm culture

Triploid papaya (Carica papaya) plants were obtained by immature endosperm culture. Visible callusing of the endosperm occurred 21 days after initiation of cultures. A continuously growing callus was observed and a maximum of 68.7% of callus induction frequency was obtained when immature endosperm with embryo was cultured on Murashige and Skoog (MS) medium containing 6.0 mu M 2,4-dichlorophenoxyacetic acid (2,4-D), 2.5 mu M alpha-naphthaleneacetic acid (NAA) and 4.0 mu M 6-furfurylamino purine (Kn). Shoot buds were produced when the callus was subcultured on a medium supplemented with 6-benzyladenine (BA) or thidiazuron (TDZ) along with NAA. Shoots were detached from the callus and transferred to the elongation medium supplemented with indole-3-acetic acid (IAA) and BA. The combination of 3.0 mu M IAA and 1.5 mu M BA was the best in terms of the number of cultures (93.8%) showing axillary shoot proliferation. The addition of 2.0 mu M indole-3-butyric acid (IBA) to the 1/2 MS medium was most effective at inducing root formation with 90% of the shoots developing four to five roots. Healthy rooted plantlets were transferred to pots containing sterilized bed soil and perlite (3:1) mixture in the greenhouse and 78% of the micropropagated plants survived transplantation. The leaves from endosperm-derived plants showed larger stomata and more chloroplasts in guard cells than that from the parent plants. Over 75% of the endosperm-derived plants were triploid with chromosome number 2n = 3x = 27.