Line breeding means keeping matings within one family or line, usually so that offspring stay closely related to one superior ancestor, without the full intensity of selfing or repeated full-sib crosses. The aim is to concentrate that ancestor's good alleles while keeping inbreeding moderate.
In practice
A cannabis breeder might have one exceptional female. Instead of selfing her, the breeder crosses her to a selected male, picks the best sons and daughters, crosses them with each other and occasionally back to her (if she is kept as a clone), and keeps several family branches going in parallel. Branches can later be crossed together to restore vigour.
Line breeding is the patient middle path between outcrossing everything and inbreeding hard. It depends on keeping enough families and records: which plant came from which cross, and how each branch performed.
Don't confuse with
- Backcross: a specific, repeated cross to one recurrent parent; line breeding is broader.
- Selfing: the most intense inbreeding.
- Line (market use): "a line" can mean any seed family; line breeding is a method.
Selfing is pollinating a plant with its own pollen, in cannabis usually by reversing part of a female to make pollen; it is the most intense form of inbreeding.A sib cross is a cross between siblings from the same seed batch, used to advance a line (F1 × F1 gives F2) while keeping it within the family.An allele is one version of a gene; a diploid cannabis plant carries two alleles at each locus, one from each parent, which may be the same or different.Inbreeding is mating between related plants, which raises homozygosity; an inbred line is the resulting population, measured by the inbreeding coefficient F.An outcross is a cross to an unrelated plant from outside the line, used to bring in new traits or vigour, or to rescue a line suffering inbreeding depression.A backcross is a cross of a hybrid back to one of its parents (or that parent's line), repeated to recover the parent's traits while keeping one introduced trait.An IBL (inbred line) is a seed line that has been inbred and selected over many generations until it breeds true for its main traits, giving uniform offspring.Selection in breeding is choosing which plants become parents, so that alleles behind the chosen traits become more common in the next generation.
