Direct organogenesis and callus induction of coconut from seed embryo for mass propagation

Abstract

Coconut (Cocos nucifera L) is an important crop in many tropical countries both for food and as a cash crop. However, coconut production in Kenya is facing challenges including lack of enough planting material, diseases and low productivity due to the senile coconut plantations. Therefore, higher efficiency of plantlet production via In vitro techniques is required for mass propagation. The purpose of this study to evaluate the regeneration potential of coconut plants via direct organogenesis and indirect somatic embryogenesis for mass production of clean planting material. For regeneration through direct organogenesis and indirect somatic embryogenesis in Euwens Y3 media, embryo explants derived from 9-12 months old coconuts were used. Direct organogenesis resulted in embryo germination and development on Euwens Y3 media supplemented with 0.28µM 2 4D, 0.44µM BAP and 0.03µM GA3 after 16 weeks of culturing in darkness. Regeneration through indirect somatic embryogenesis was established in Euwens Y3 medium supplemented with 100 to 250µM 2, 4 -dichlorophenoxyacetic acid (2, 4-D) alone and in combination with 0.35µM and 0.5µM Gibberellic acid (GA3), 5µM 6-Benzylaminopurine (BAP) and 9µM Thiadiazuron (TDZ). The highest callus induction was observed in medium containing 150µM 2, 4-D + 5µM BAP while the least was in 2, 4-D alone, and in combination with 0.35µM GA3. Highest embryogenic calli were observed in media containing 75µM 2, 4-D + 5µM BAP and the least was in medium containing 2, 4-D alone and in combination with 0.35µM GA3. Multiple shoot maturation was observed in medium containing a combination of 10µM kinetin, 10µM BAP, 0.5µM GA3, and 200µM NAA. Maximum shoot elongation (3.63cm) was recorded in medium containing 10µM BAP and the least (3.06 cm) was in medium with 5µM BAP. Rooting was done in Euwens Y3 medium containing Indole-3-butyric acid (IBA). The highest response was observed in Euwens Y3 medium supplemented with 5µM IBA+ 0.5µM GA3 both with respect to the number of roots 8.33 and root length 5.10 cm while the least was with 15µM IBA+ 0.5µM GA3 with regard to the number of roots (3.33) and root length 2.83cm. Tissue culture plantlet acclimatization was achieved in soil: sand: manure ratio (3:1:1) gave a 60% survival rate and vermiculate medium had 50% survival rate. Hence, In vitro regeneration of coconut through somatic embryogenesis and direct organogenesis is possible and can be used as an alternative to provide tissue culture plantlets for mass production.