Somaclonal variation is change that arises in plants grown back from tissue culture. It ranges from DNA mutations and chromosome changes to epigenetic shifts in gene activity. It is most common when plants are regenerated from callus (undifferentiated cell masses) and after many subculture cycles, and least common in shoot-tip and meristem culture, which keeps organised tissue.
In practice
For preservation, somaclonal variation is a risk to manage. Labs reduce it by using meristem or shoot-tip culture instead of callus, limiting the number of subcultures, keeping growth slow, and checking regenerated plants against the original, by eye and ideally by DNA fingerprinting (Monthony et al. 2021).
Some breeders in other crops use it deliberately as a source of new variation. That is not the aim when the job is to keep a clone exactly as it is.
Don't confuse with
- Genetic drift: a population-level process in seed lines.
- Topophysis: position effects in cuttings, without tissue culture.
- Clone decline: almost always pathogens or care in cuttings; somaclonal variation is specific to regenerated tissue culture plants.
Tissue culture is growing small pieces of a plant on sterile nutrient gel in a sealed vessel, used to multiply, clean up and store cannabis genotypes.A chromosome is one long DNA molecule packaged with proteins that carries many genes; cannabis normally has 10 pairs, nine autosome pairs plus an X/Y sex pair.A gene is a stretch of DNA that carries the instructions for one functional product, usually a protein such as an enzyme, and is the basic unit of inheritance.Meristem culture is tissue culture from the tiny dome of dividing cells at a shoot tip, used to regenerate plants free of viroids and viruses.Genotyping is reading a plant's DNA at selected markers to identify it, compare it with other plants, check sex or chemotype, or estimate its ancestry.Genetic drift is random change in allele frequencies between generations of a seed population, strongest in small populations; clones do not drift this way.Topophysis is the tendency of cuttings to keep traits linked to the position on the mother plant they were taken from, so cuts from different parts can behave differently.A mutation is a change in a plant's DNA sequence, arising in seed or in one branch (a somatic mutation); mutations are rare and usually neutral.A polyploid plant carries more than two full sets of chromosomes, such as a triploid (three) or tetraploid (four); in cannabis these are almost always bred deliberately.
