Somatic embryogenesis in papaya (Carica papaya L. cv. Rathna)

Abstract

A protocol was developed for somatic embryogenesis from zygotic embryos, hypocotyl explants from in vitro seedlings and leaf explants from greenhouse grown plants of Carica papaya L. cv. Rathna. Seeds in which the sarcotesta membrane is removed, were germinated in conical flasks with sterilized water and maintained on an orbitral shaker, and within 2-4 week were used to excise hypocotyls explants. Zygotic embryos were isolated directly from sterilized seeds. Embryogenic calli from zygotic embryos and hypocotyl explants were initiated successfully on Murashige and Skoog (MS) medium containing 3 mgL-1 Naphthalene Acetic Acid (NAA) when compared with MS medium containing combination of 3 mgL-61 NAA and 2 mgL-1 2,4 Dichlorophenoxyacetic acid (2,4-D). Induction of embryogenic calli from mature and immature leaf explants were evaluated on media supplemented with 3 mgL-1 NAA, 3 mgL-1 Indole-3-butyric acid (IBA) and 1 mgL-1 2,4-D. Immature leaf explants cultured on 1 mgL-1 2,4-D was found to be the most suitable for callusing. Effect of 100 mgL-1 Casien hydrolysate, 0.1 mgL-1 Abscisic acid (ABA), 0.5 mgL-1 6-Benzylaminopurine (BAP) and hormone-firee MS media were tested for the maturation of calli and for the formation of somatic embryos. Casein hydrolysate was found to be the most suitable for maturation of calli. Matured embryogenic calli could be proliferated on MS medium supplemented with 0.5 mgL-1 BAR Germination of embryos was evaluated in 0.1 mgL-1 BAP and 0.1 mgL-1 NAA combination, 0.02 mgL-1 NAA and 0.5 mgL-61 BAP as well as in hormone-free MS medium. The medium supplemented with 0.02 mgL-1 NAA and 0.5 mgL-1 BAP combination gave significantly higher germination. Further development of plantlets was achieved through germination of somatic embryos on hormone-free MS medium. Sixty percent of the plantlets could be successfully acclimatized on coir dust: sand=1:1 medium in a propagator.