Tissue culture protocol for propagation of coconut via somatic embryogenesis of plumule explants

The coconut is a very important export crop of the Philippines. Coconut oil is the main product of the industry and most recently, the very popular virgin coconut oil which is being used just like medicine of food supplement for certain ailments. The coconut is propagated mainly by seed which is highly variable and quite slow since one plant is obtained from one seed. The Philippines has quite a number of outstanding coconut cultivars and it is important these cultivars be propagated vegetatively especially if there is a need to rehabilitate a plantation or to establish a new one. Under ordinary conditions, the coconut plant cannot be propagated vegetatively. The only alternative is through biotechnology via tissue culture. The primary aim of this study is to develop an efficient tissue culture system for coconut via somatic embryogenesis of plumule (shoot tip) explants. This will be useful not only as a system for micropropagation of uniform and elite stocks, but also for in vitro conservation and genetic transformation with improved characteristics. The authors are conducting this biotechnology study in collaboration with other groups to further improve the tissue culture protocol for coconut. Fresh and pre-germinated coconut embryos from 'Makapuno', 'Laguna Tall' and Baybay Tall' served as sources of plumule for in vitro culture. Twenty-three batches of plumule experiments were conducted with a total of 1,794 cultures. Seven different base media, which included BP (Barba and Patena, 2002) medium, Y3 (Euwen's, 1976) medium, modified BP medium(1, 2, and 3) MS (Murashige and Skoog, 1962) medium and B and B (Branton and Blake, 1984) medium were used for calloid induction. The base media were supplemented with 2,4-D or growth regulators T or D and BAP or 2-ip. Results showed that calloid induction and increase in calloid weight were best in BP and Y3 media. Moreover, eight media treatments were tested for three consecutive subcultures on pre-germinated 'Makapuno' embryos to test the effect of base medium (B and B, MS, Y3 and BP medium) and differences in casein enzymatic hydrolysate (0.3 and 0.6 g/L) on calloid weight and formation. Increase in calloid weight ranged from 75.9 mg in MS medium with 0.3 g/L casein hydrolysate to 125 mg in B and B medium with 0.3 g/L casein hydrolysate. In terms of calloid formation, B and B medium with 0.3 g/L casein hydrolysate also gained the highest formation (74.30 percent) while Y3 medium with 0.6 g/L casein hydrolysate was the lowest at 23 percent formation. Browning incidence was greatest in Y3 medium. Calloid formation of most of the cultures was still rated 1, i.e. less than 1/2 of the initial explant was covered with calloid. This was based on the 'Terminologies and Criteria for Morphological Characterization of Coconut Cultures, Prior Art of Coconut Tissue Culture and Pathways for Somatic Embryogenesis' which the Coconut Tissue Culture Team (DOST-PCARRD-PCA and CSC-IPB-UPLB Project personnel) formulated during the workshop held on 18-20 July 2005 at PCA-Albay.