Application of un-fertilized ovary culture to identify elite mother palms of Cocos nucifera L. with regenerative potential

Abstract

Un-fertilized ovary is a promising explant for micropropagation of coconut. However, due to high heterozygocity in coconut, in vitro performance varies greatly among palms. In this study, callogenesis, somatic embryogenesis and plant regeneration potential of 35 Sri Lanka Tall (SLT) and 20 Dwarf x Tall hybrid (DxT) elite palms were assessed to select suitable mother palms for clonal propagation. Callusing was induced from ovaries excised from immature female flowers, cultured on CRI 72 basal medium containing 100 μM of 2,4 dichlorophenoxy acetic acid (2,4-D), 9 μM of thidiazuron and activated charcoal at 0.1 %. The induced calli were proliferated in two cycles. Somatic embryos were induced in low 2,4-D (66 μM) medium and matured in hormone-free medium with a consecutive transfer to a medium with 20 μM of 2-isopentyladenine. Germination of somatic embryos and the development of shoots occurred in Y3 medium with 0.45 μM of gibberellic acid. Ovaries of SLT and DxT palms initiated callusing by 74.0 and 65.0 %, respectively. Percentage of explants that developed callus varied from 4 to 50 % in SLT and 9 to 57 % in DxT. Calli of DxT did not grow further to regenerate somatic embryos. However, SLT calli proliferated in two cycles and regenerated a mean of 12.5 well-developed embryogenic structures per ovary. The maximum welldeveloped embryogenic structures obtained were 70 in few ovaries. Twelve out of 35 SLT palms regenerated shoots with the number of shoots per inflorescence ranging from 1 to 205. The results showed that not only individual palms but also individual explants respond differently to in vitro culture. The study enabled identification of 12 SLT palms as responsive to in vitro culture.