Cannabis is dioecious — separate male and female plants. Hermaphroditism is common and can ruin harvests.
1. Sex System
- Female (
): Produces buds with highest cannabinoid content - Male (
): Produces pollen sacs. One male can pollinate entire grow room → 30-50% cannabinoid loss - Hermaphrodite: Both male and female flowers on one plant
XY Chromosome System
XX = Female, XY = Male. Large X-specific (non-recombining) region; possibly the oldest plant sex-chromosome system documented so far (Prentout et al., 2020)
Monoecy1 Locus (2025 Study)
- On the X chromosome (about 2 Mb region); candidate genes CsREM16, lncREM16, CsKAN4 (Toscani et al., New Phytologist 2026)
- Proposed, not yet shown by experiment: changes here let XX plants of monoecious cultivars form male flowers
- Not an ethylene gene: CsETR1 and CsACS3 lie outside the locus
CsETR1 — Ethylene Receptor
- High ethylene → female expression
- STS blocks CsETR1 → female plants produce X-bearing pollen → feminized seeds
2. Sex Identification Methods
| Method | Accuracy | Earliest Time | Cost | Best For |
|---|---|---|---|---|
| Preflower observation | 85-90% | Week 4-6 veg | Free | Small growers |
| 12/12 from seed | ~95% | Day 10-14 | Free (yield loss) | Large screening |
| PCR/DNA test | 99.5%+ | Day 5-7 | $5-15/sample | Commercial/breeding |
3. Hermaphroditism
Genetic Hermaphroditism
Mo1 mutation, unstable genetics. Remove immediately.
Stress-Induced Triggers:
- Light leaks (#1 cause)
- Temperature >30°C in flowering
- K deficiency
- Late harvest → “nanners”
- pH fluctuation >±1.0
Hormone Mechanism
Stress → ethylene drops → gibberellin rises → male flowers (survival mechanism)
4. Feminized Seeds
| Feature | STS | Colloidal Silver |
|---|---|---|
| Feminized rate | 99.7-99.9% | 95-99% |
| Sprays needed | 2-3 | 14-21 daily |
| Best for | Professional breeders | Home growers |
5. Management Strategy by Scale
| Scale | Seed Type | Testing | Notes |
|---|---|---|---|
| Personal (1-10) | Feminized | Visual preflower | Check daily week 1 flowering |
| Medium (10-50) | Fem + Regular | PCR + visual | PCR for regulars |
| Commercial (50+) | Feminized (STS) | PCR mandatory | Zero tolerance |
| Breeding | Regular | PCR + phenotype | Isolate males ≥300m |
Anti-Herm Checklist
- ✓ Check light leaks before each cycle
- ✓ Flowering temp 20-26°C, max 28°C
- ✓ Stable pH: ±0.3 hydro, ±0.5 soil
- ✓ Harvest on time
- ✓ Choose stable genetics
- ✓ Daily inspection first 2 weeks of flowering
6. Trends 2024-2026
- CRISPR Mo1 knockout for herm-free strains
- Epigenetic herm-potential testing
- Field LAMP assay: 30-min sex test without lab
- AI preflower recognition: ~92% accuracy
References
- Prentout et al. (2020). An efficient RNA-seq-based segregation analysis identifies the sex chromosomes of Cannabis sativa. Genome Research, 30(2), 164-172.
- Prentout et al. (2021). Plant genera Cannabis and Humulus share the same pair of well-differentiated sex chromosomes. New Phytologist, 231(4), 1599-1611.
LEGAL DISCLAIMER: Educational & scientific purposes only. Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568 & Ministerial Regulation B.E. 2569. Commercial sale, processing and export of cannabis flower require a licence; PT 33 (ภ.ท. 33) is the prescription form for dispensing cannabis flower, not a cultivation permit. No recreational use promotion.