Induction of somatic embryogenesis in Papaya (<em>Carica papaya</em>)

Abstract

This study highlights the induction of somatic embryogenesis using immature zygotic embryos of Carica papaya commercial varieties viz. Coorg Honey dew, Washington, Honey dew, Pusa delicious, Pusa nanha, Taiwan 786, Taiwan 785, Sunrise, Solo, Co-1, C0-7, and Co-3 respectively. Somatic embryos formed in the presence of thidiazuron (TDZ) in combination with 2, 4-dichlorophenoxy acetic acid (2, 4-D), but never on  explants cultured on control medium lacking plant growth regulators. Embryogenic callus could be induced from immature zygotic embryos after 4-6 weeks of culture on full-strength Murashige and Skoog inorganic salts, which served as the basal medium supplemented with 4.52 μM 2, 4-D and 2.27 μM TDZ (induction and maintenance medium). The ability to induce  embryogenic tissue varied for different papaya tested varieties, and there was a mixed genotypic response on the induction of embryogenic cultures. The highest percentage of somatic embryogenesis was noticed in a papaya variety Taiwan-786 (87.0±4.2a), followed by Taiwan- 785  (85.0±3.0a), and Coorg Honey dew (81.0±3.2a) respectively. This protocol is simple and reproducible, and could be useful for regenerating large number of plants as well as provide a target tissue for genetic  transformation experiments.