Here’s a detailed overview of organogenesis and somatic embryogenesis in Aquilaria spp., with emphasis on techniques, applications, and challenges. I’ll break it down systematically for clarity:
1. Background
Aquilaria species (e.g., Aquilaria malaccensis, A. sinensis, A. agallocha) are highly valued for agarwood production. Due to overharvesting and slow growth, biotechnological propagation methods like organogenesis and somatic embryogenesis are crucial for conservation, large-scale propagation, and uniform planting material.
2. Organogenesis in Aquilaria spp.
Definition
Organogenesis is the process where shoots or roots are regenerated from explants (tissue segments) via dedifferentiation and redifferentiation under controlled in vitro conditions.
Explants Used
- Nodal segments
- Shoot tips
- Leaf segments
- Petiole segments
- Stem sections
Key Steps
- Explant sterilization: Critical to prevent microbial contamination.
- Callus induction (if needed): Some explants require a callus phase before organ formation.
- Shoot induction:
- Media: Murashige & Skoog (MS) or Woody Plant Medium (WPM)
- Plant growth regulators (PGRs):
- Cytokinins: BAP (6-Benzylaminopurine), kinetin → promote shoot formation
- Auxins: NAA (Naphthaleneacetic acid), IBA (Indole-3-butyric acid) → support root initiation
- Root induction: Usually requires auxin-rich media.
- Acclimatization: Gradual transfer to ex vitro conditions.
Highlights & Findings
- High regeneration efficiency has been reported using nodal explants on MS media supplemented with 1–2 mg/L BAP and 0.1–0.5 mg/L NAA.
- Leaf explants tend to produce callus first, which then differentiates into shoots.
Applications
- Mass propagation of elite genotypes
- Germplasm conservation
- Production of uniform planting material for agarwood cultivation
3. Somatic Embryogenesis in Aquilaria spp.
Definition
Somatic embryogenesis is the formation of embryos from somatic cells, bypassing seed formation. These embryos can develop into full plants.
Explants Used
- Leaf tissue
- Cotyledonary tissue
- Immature zygotic embryos
- Callus derived from stems or petioles
Key Steps
- Callus induction
- Medium: MS or WPM with high auxin concentration (e.g., 2,4-D at 1–3 mg/L)
- Duration: 4–6 weeks until friable callus forms
- Somatic embryo induction
- Reduce auxin levels or combine with cytokinins (BAP, kinetin)
- Embryos develop in globular → heart → torpedo → cotyledonary stages
- Maturation
- Media may contain ABA (abscisic acid) to promote embryo maturation
- Germination
- Transfer embryos to hormone-free or low-hormone medium for plantlet development
- Acclimatization
- Gradual adaptation to soil and greenhouse conditions
Highlights & Findings
- Both direct and indirect embryogenesis reported:
- Direct: Somatic embryos develop directly from explant cells (rare)
- Indirect: Callus formation first → somatic embryos (common in Aquilaria)
- Efficient regeneration observed with 2,4-D for induction and BAP for conversion.
- Somatic embryos allow synthetic seed production, enabling storage and transport.
Applications
- Clonal propagation of superior agarwood-producing trees
- Conservation of endangered Aquilaria species
- Synthetic seed production for large-scale plantation
4. Challenges
- Contamination during tissue culture
- Genotype-dependent response: Not all Aquilaria species respond equally
- Somaclonal variation in regenerated plants
- High cost and labor intensity
- Rooting and acclimatization can be difficult due to woody nature
5. Future Prospects
- Automation & bioreactors: Mass-scale organogenesis and somatic embryogenesis
- Genetic improvement: Combine tissue culture with molecular breeding for disease resistance or faster agarwood formation
- Synthetic seed technology: For storage, transport, and large-scale planting
- Secondary metabolite enhancement: Inducing agarwood resin biosynthesis in vitro using elicitors or microbial inoculation
References / Key Studies
- Chaturvedi, C. M. et al., 2008. In vitro regeneration of Aquilaria agallocha Roxb. from nodal segments. Plant Cell Tissue Organ Cult.
- Liu, Y. et al., 2013. Somatic embryogenesis and plant regeneration of Aquilaria sinensis. Sci. Hortic.
- Purohit, S. D. et al., 2011. Clonal propagation of Aquilaria malaccensis through organogenesis. Plant Biotechnol. Rep.