Somatic embryogenesis and plant regeneration from unfertilised ovary explants of coconut (Cocos nucifera L.).

Unfertilized ovaries excised from immature female flowers of adult coconut palms (variety Sri Lanka Tall) were cultured in CRI 72 medium supplemented with 100 µM 2,4-dichlorophenoxyacetic acid (2,4-D) for callus induction. Five culture procedures including the standard procedure were tested for induction of somatic embryogenesis and plant regeneration. In the standard procedure, the calli were transferred to CRI 72 medium with 5 µM abscisic acid (ABA) and high agar concentration (2%) (w/v) for two weeks, CRI 72 medium with 5 µM ABA and normal agar concentration (0.55%) (w/v) for further three weeks, maturation medium (CRI 72 medium without any hormones) for four weeks and germination medium (modified Eeuwens Y 3 medium supplemented with 5 µM 6-benzyl aminopurine (BAP) and 0.1 µM 2,4-D). In the other four procedures, modifications to the standard procedure were done by eliminating certain steps and incorporating 5 µM 2- isopentyl adenine (2iP) into the germination medium. In all five procedures, very poor shoot formation was observed but could be improved by incorporating 0.35 µM gibberelic acid (GA 3 ) into the germination medium. The highest percentage of shoot regeneration (85%) was achieved by sub-culturing the embryogenic calli directly into the modified Eeuwens Y 3 medium devoid of any growth regulators for four weeks followed by sub-culturing into germination medium supplemented with 5 µM 2iP, 0.1 µM 2,4-D and 5 µM BAP and finally to germination medium with 0.35 µM GA 3 . The results clearly indicated the positive effect of 2iP and GA 3 on plant regeneration in ovary-derived calli of coconut.