Optimization of rhizogenesis in oil palm (Elaeis guineensis Jacq.) vitro plantlets derived from direct organogenesis of mature zygotic embryos (MZE)

Abstract

Optimization of rhizogenesis in oil palm (Elaeis guineensis Jacq.) vitro plantlets derived from direct organogenesis of mature zygotic embryos (MZE) 234 Citation: Kingsley TM, Godswill1 NN, Brice1 TL, et al. Optimization of rhizogenesis in oil palm (Elaeis guineensis Jacq.) vitro plantlets derived from direct organogenesis of mature zygotic embryos (MZE). A. In vitro plantlet whose differentiation resulted into a shoot bud only (Type 1 explants); B. B. In vitro plantlet with complete differentiation in to a root and a shoot bud (Type 2 explants). 1) Remnants of haustorium ; 2) Shoot bud ; 3) Primary horizontal root ; Bar= 5 mm Results The complete absence of a root axis (Figure 1A) for over 70 % of differentiated MZE was observed to be a major constraint in the production of in vitro oil palm plantlets via direct organogenesis of MZE. Roots induction in Type 1 explants (Figure 1A) as well as the growth of roots in Type 2 explants (Figure 1B) was highly influenced by the type and concentration of auxin supplement in full MS medium. In all culture media that received IAA and NAA, no root induction was observed (Figure 2A) within the study period as in the controls where no auxin was added. Out of the three types of auxins employed, only IBA let to roots induction (Figure 2B) in Type 1 explants. However, significant differences were observed in rate of root induction among the different concentrations of IBA. Root induction scores of 50 %, 25 % and 0 % were recorded in MS medium supplemented with 1.5 mg L-1 , 1 mg L-1 and 0.5 mg L-1 respectively (Table 2). The emerged roots were healthy, robust and contained many secondary roots as well (Figure 2B). As far as growth and development of roots (Figure 2C) in plantlets derived from Type 2 explants is concerned, no increase in root length was observed in explants inoculated in the control and IAA supplemented media. On the other hand, NAA at concentrations of 1.0 and 1.5 mg L-1 showed an average increase of 5 % in initial length. The samples inoculated in 1.5 mg L-1 IBA showed a significant increase of 100 % over their initial length (Table 2). Similarly, the rate of proliferation of root hairs was more profuse in 1.5 mg L-1 IBA compared to other auxins regardless of the concentrations. No root hair development was observed in the control and culture media supplemented with IAA. Table 2 Effect of auxin types on root induction and development of vitro plantlets Control IAA IBA NAA 0 1 2 3 4 5 6 7 8 9 Shoots (Lot1) that rooted (%) 0 0 0 0 0 16 50 0 0 0 Mean increase in initial length (%) for Lot 2 0 0 0 0 10 25 100 0 10 10 Proliferation of root hairs for Lot 2 0 0 0 0 + + + + + + + + + + + + + + Numbers 0-9 represent different experiments + rate of root hair proliferation Figure 2 Rhizogenesis response of Types 1 and 2 explants to auxin: A. Failure to induce roots in Lot 1; B. Induction of roots from Type 1 explants (notice the complete whitish nature of the root); C. Elongation of roots in Type 2 explants (notice the brownish colour of the upper part and the whitish colour of the lower part of the roots). Bar= 1 cm. In the course of acclimatization, a survival rate of 66.7% was achieved. When plantlets were transferred in polybags with natural soil, the survival rate was 74.1 %. These plantlets were subsequently planted in an experimental field to record their growth parameters, flowers and fresh fruits bunch production.