🌱 1. Plant Tissue Culture — Overview
Plant tissue culture is the in-vitro growth of plant cells, tissues, or organs on
a nutrient medium under sterile conditions. Key stages:
- Explant preparation — select healthy donor tissue.
- Sterilisation — surface-sterilise (NaOCl, HgCl₂, ethanol).
- Inoculation — place on culture medium (MS, B5, N6).
- Callus induction — dedifferentiation on auxin-rich medium (2,4-D, NAA).
- Regeneration — shoot/root organogenesis on cytokinin-rich medium (BA, Kinetin).
- Rooting & acclimatisation — hardening of plantlets before transfer to soil.
Key idea: The ratio of auxin to cytokinin determines the developmental fate:
high auxin → callus / roots; high cytokinin → shoots; balanced → callus.
🦠 2. Contamination Monitoring
Input format
Treatment Total_explants Bacterial_count Fungal_count
What each metric means
- Total contamination % = (bacterial + fungal) / total × 100.
- Bacterial contamination — cloudy medium, slimy growth, often from Bacillus, Pseudomonas.
- Fungal contamination — fuzzy, spreading growth, often from Aspergillus, Penicillium, Fusarium.
- Clean % — success rate of the sterilisation protocol.
Interpretation thresholds
| Contamination % | Assessment | Action |
|---|
| 0% | Perfect sterility | Continue protocol. |
| ≤ 5% | Good | Routine monitoring. |
| 5–15% | Acceptable | Check laminar flow, autoclave. |
| 15–30% | Poor | Revise sterilisation time/concentration. |
| > 30% | Failed | Stop, re-design protocol. |
Bacterial vs fungal: Bacteria usually come from inadequate surface sterilisation
or handling; fungi often from airborne spores in the laminar hood.
Match the fix to the cause.
🌾 3. Callus Induction Assessment
Input format
Treatment Explants Callus_formed FW_mg Score(0-5) Days
Metrics
- Induction % = callus / explants × 100. Primary success measure.
- Fresh weight (FW) — total callus mass; reflects proliferation.
- FW per callus — average mass per callus; large values = vigorous callus.
- Visual score (0–5) — 0 = no callus, 5 = excellent friable callus.
- Days to induction — earlier = better (fast response).
- Efficiency Index — composite: (Induction% × FW × Score) / Days.
Interpretation of visual score
| Score | Description |
|---|
| 0 | No callus — explant unchanged or dead. |
| 1 | Very poor — few cells dividing at cut edges. |
| 2 | Poor — small, compact callus. |
| 3 | Moderate — visible callus at 25–50% of explant. |
| 4 | Good — callus covering >50%, friable. |
| 5 | Excellent — abundant friable callus, ideal for regeneration. |
Interpretation of Induction %
| Induction % | Assessment | Action |
|---|
| ≥ 80% | Excellent | Use this hormone combination. |
| 50–80% | Good | Try optimising auxin concentration. |
| 30–50% | Fair | Change auxin type (2,4-D ↔ NAA). |
| < 30% | Poor | Reconsider explant type or medium. |
🌿 4. Regeneration Efficiency
Input format
Treatment Calli Shoots Roots Plantlets
Metrics
- Shoot regeneration % = shoots / calli × 100.
- Root regeneration % = roots / calli × 100.
- Shoots per callus — multiplication factor (higher = more efficient).
- Full plantlet % = plantlets / calli × 100 — the ultimate measure.
Interpretation of Full Plantlet %
| Full plantlet % | Assessment | Comment |
|---|
| ≥ 60% | Excellent | Publishable protocol; consider scaling. |
| 40–60% | Good | Optimise for higher rate. |
| 20–40% | Fair | Adjust cytokinin / auxin ratio. |
| < 20% | Poor | Change growth regulators or explant source. |
Cytokinin choice matters: BA (benzyladenine) is most common; TDZ can boost
recalcitrant species; Kinetin is gentler. Add a low auxin (NAA, IAA) for
shoot elongation and rooting.
📈 5. Root / Shoot Growth Analysis
Input format
Week Shoot_length_cm Root_length_cm Shoot_FW_g Root_FW_g
Why measure growth rate?
- Growth rate (slope) — cm/week or g/week. Compare treatments objectively.
- R² of regression — indicates whether growth is linear (steady-state) or
non-linear (stress, transition).
- Root:Shoot ratio — physiological indicator of stress tolerance.
High R:S = stress or deficiency; low R:S = favourable culture.
Interpreting R²
| R² | Interpretation |
|---|
| ≥ 0.95 | Excellent linear growth — steady exponential phase. |
| 0.85–0.95 | Good fit — minor deviations. |
| 0.70–0.85 | Moderate — growth slowing or speeding up. |
| < 0.70 | Poor — non-linear growth; consider logistic / polynomial fit. |
Root:Shoot ratio interpretation
| Root:Shoot | Meaning |
|---|
| < 0.5 | Shoot-dominant — typical of tissue culture. |
| 0.5 – 1.0 | Balanced growth — healthy plantlets. |
| 1.0 – 2.0 | Root-dominant — sometimes a stress response. |
| > 2.0 | Strongly root-dominant — check nutrient balance. |
🔬 6. Statistical Design & Pitfalls
Replication
- Biological replicates — different explants / plants (minimum n = 3).
- Technical replicates — repeated measurements on the same sample.
- Always report mean ± SE or mean ± SD with n.
Recommended statistical tests
| Question | Test |
|---|
| Compare 2 means | t-test (independent or paired) |
| Compare 3+ means | One-way ANOVA + Tukey/Duncan post-hoc |
| Compare 2+ factors | Two-way ANOVA |
| Compare proportions | Chi-square or Fisher's exact |
| Growth over time | Linear mixed model or repeated-measures ANOVA |
Common pitfalls
Pseudo-replication: Many explants from the same donor is not true replication.
Use independent donor plants.
Inherited contamination: A donor plant carrying latent bacteria can contaminate
every subculture. Index the mother plant.
Reporting only %: Percentages without denominators are meaningless. Always report
n (e.g. "75% (30/40)").
Ignoring acclimatisation: Regeneration success ends at ex vitro survival,
not at rooting. Track hardening survival.
Best practice: Report mean ± SE, include representative photographs, describe
the medium composition, and demonstrate reproducibility across ≥2 independent experiments.
Reporting checklist for a tissue-culture paper
- ✔ Donor species / cultivar and explant source
- ✔ Sterilisation protocol (agent, concentration, time)
- ✔ Medium composition (MS/B5/N6, hormones, gelling agent)
- ✔ Culture conditions (light, temperature, photoperiod)
- ✔ Number of replicates (biological and technical)
- ✔ Statistical tests used
- ✔ Contamination rates, induction %, regeneration %, acclimatisation %
- ✔ Representative photographs of each stage