An outcross is a mating between a plant in a breeding line and an unrelated plant from outside it. The aim is to bring in alleles the line lacks: a resistance, a flavour, earlier finishing, or simply fresh heterozygosity.
In practice
Outcrossing is the standard cure for inbreeding depression. A line that has been sib crossed or selfed for several generations and has lost vigour, seed set or germination often bounces back in a single outcross. The cost is uniformity: the outcross reshuffles everything, so the breeder usually follows it with backcrosses to the original line to recover its type while keeping the new trait.
Breeders also use "outcross" for crossing to a different population or type, for example a landrace into a modern hybrid line. That can dilute the landrace if the seed is then sold or released under the landrace's name, which is one way source-region gene pools get contaminated.
Don't confuse with
- Backcross: crossing back to a parent or the original line, the opposite direction.
- Line breeding: crossing within related plants; outcrossing goes outside.
- Hybrid: the product of any cross between different parents. An outcross produces hybrids by definition.
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.A plant is heterozygous at a locus when it carries two different alleles there (Aa), so its offspring can inherit either one and segregate.Inbreeding depression is the loss of vigour, fertility, yield or survival that follows mating between relatives, mainly because harmful recessive alleles become homozygous.Germination is the stage where a viable seed absorbs water, splits its shell and pushes out a root (radicle), usually within 1-7 days at 20-30 °C.A landrace is a traditional, locally adapted cannabis population kept by farmers in one region over many generations, with its own type and plenty of internal variation.The gene pool is the total set of alleles present in a population, cultivar group or species; a narrow gene pool limits what breeders can select from.Line breeding is a mild form of inbreeding in which plants are mated within a family, often back towards one outstanding ancestor, to concentrate its traits while limiting inbreeding.A hybrid is the offspring of two genetically different parents; almost all modern cannabis is hybrid, built from crosses between landrace-derived and other lines.A cross is the offspring of mating two different plants, written female x male, as "A x B"; one cross starts a line but is not one.Heterosis (hybrid vigour) is the tendency of offspring from genetically different parents to outgrow or outperform both parents in traits such as vigour and yield.Introgression is the movement of genes from one population or type into another through hybridisation followed by repeated backcrossing.
