Short answer. Landraces are regional populations shaped by local farmers and climate over many generations: variable, adapted, and genetically distinct from each other. Polyhybrids are modern mixes of many such sources: often more productive in indoor conditions, but heterozygous, so their seed scatters. Neither is "better". Landraces are where new traits live; polyhybrids are where most modern selection happens.
Definitions
- Landrace: a dynamic population with historical origin, distinct identity, local adaptation and association with traditional farming, usually lacking formal improvement [1].
- Heirloom / heritage line: a line kept for decades (often outside its origin) by growers or seed collectors. It may descend from a landrace but has been through new selection and bottlenecks. Not the same thing.
- Polyhybrid: a line whose pedigree combines many unrelated ancestors. Most commercial "strains" today [3][6].
Comparison
| Feature | Landrace (in origin) | Heirloom import | Polyhybrid |
|---|---|---|---|
| Genetic variation within | Moderate to high, but coherent | Often reduced (founder bottleneck) | High heterozygosity per plant |
| Uniformity from seed | Moderate | Variable | Low |
| Adaptation | Local climate, day length, pests | Partly lost outside origin | Indoor production |
| Flowering time | Often long (tropical) or short (high latitude) | As origin | Bred for 8-10 weeks typically |
| Value to breeders | Novel alleles, resistance, unusual chemistry | Historical reference | Elite combinations to select from |
| Conservation status | Many endangered by hybrid replacement [2] | Small populations, drift | Abundant |
McPartland and Small (2020) describe several high-THC landrace groups as critically endangered germplasm and note that widespread hybridisation over the past 50 years has blurred distinctions [2] (Supported).
Why polyhybrid seed scatters
A polyhybrid clone may be heterozygous at a large share of its genes. Crossing two such clones produces offspring that reshuffle many alleles at once, so the "F1" behaves like an F2 (see F1, F2, F3). Genetic studies show commercial drug-type cannabis is a mixed gene pool in which reported ancestry and genetic structure only partly agree [6] (Supported).
Preserving a landrace properly
- Keep population size up. Grow and cross as many plants as you can, ideally ≥20-50 females and ≥10-20 males per generation; bottlenecks lose rare alleles (Supported by general conservation genetics) [5].
- Avoid strong selection for your own preferences; you are conserving, not improving. Remove only diseased or off-type plants (pollen contamination).
- Pool pollen from many males, or do many pair crosses and bulk the seed.
- Isolate from other cannabis.
- Document origin claims: where collected, when, by whom, and how many seeds, as GB-DOCs. Unverified origin = L1 at best.
- Store seed properly and regenerate before germination falls (see seed testing).
Using a landrace in breeding
- Cross landrace x elite, then backcross to the elite while selecting for the landrace trait (see backcrossing).
- Expect long flowering, tall stretch or different chemistry in early generations.
- Check legality and benefit-sharing rules for collected material from other countriesbeing reviewed.
Common mistakes
- Calling a 1990s seed-bank line a "pure landrace". Usually it is an heirloom with its own history.
- "Preserving" a landrace by keeping one female and one male.
- Treating a landrace's variation as a defect. It is the point.
Evidence
- Landrace definition: Established (plant genetic resources literature) [1].
- Endangered status of cannabis landraces: Supported [2].
- Commercial cannabis as a mixed, heterozygous gene pool: Supported [3][6].
- East Asian domestication origin: Contested [4].
- Population-size guidance: Supported by general genetics [5]; exact numbers are rules of thumb.
