Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

progeny to the mother plant. This parent is known as the recurrent parent. The nonrecurrent parent is called the donor parent. More widely, any time a generation is crossed to a previous generation, it is a form of backcross breeding. Backcross breeding has become one of the staple methods clandestine cannabis breeders use, mainly because it is a simple, rapid method when using greenhouses or growrooms, and requires only small populations. The principal goal of backcross breeding is to create a population of individuals derived mainly from the genetics of one single parent (the recurrent parent).
    The donor parent is chosen based on a trait of interest that the recurrent parent lacks; the idea is to introgress this trait into the backcross population, such that the new population is comprised mainly of genetics from the recurrent parent, but also contains the genes responsible for the trait of interest from the donor parent.

Sprayed with ‘Stamen-It!’ from PG-Solutions, this plant that started out as a female is now expressing only male flowers.
    The backcross method is a suitable scheme for adding new desirable traits to a mostly ideal, relatively true-breeding genotype. When embarking on a backcross breeding plan, the recurrent parent should be a highly acceptable or nearly ideal genotype (for example, an existing commercial cultivar or inbred line). The ideal traits considered for introgression into the new seed line should be simply inherited and easily scored for phenotype. The best donor parent must possess the desired trait, but should not be seriously deficient in other traits. Backcross line production is repeatable, if the same parents are used.
    Backcross breeding is best used when adding simply inherited dominant traits that can easily be identified in the progeny of each generation (Example 1). Recessive traits are more difficult to select for in backcross breeding, since theirexpression is masked by dominance in each backcross to the recurrent parent. An additional round of open pollination or sib-mating is needed after each backcross generation, to expose homozygous-recessive plants. Individuals showing the recessive condition are selected from F2 segregating generations and backcrossed to the recurrent parent (see Example 2).
Example 1- Backcrossing: Incorporating A Dominant Trait
    Step 1 - Recurrent Parent × Donor Parent - > F1 Hybrid generation
    Step 2 - Select desirable plants showing dominant trait, and hybridize selected plants to recurrent parent. The generation produced is denoted BC1 (some cannabis breeders break from botanical convention and denote this generation B×l. [BC1=B×1]).
    Step 3 - Select plants from BC1 and hybridize with the recurrent parent; the resulting generation is denoted BC2.
    Step 4 - Select plants from BC2 and hybridize with the recurrent parent; the resulting generation is denoted BC3.
Example 2 Backcrossing: Incorporating A Recessive Trait
    Step 1 - Recurrent Parent × Donor - > F1 Hybrid generation
    Step 2 - Select desirable plants, and create an F2 population via full sib-mating.
    Step 3 - Select plants showing the desired recessive trait in the F2 generation, then hybridize selected F2-recessive plants to the recurrent parent. The generation produced is denoted BC1.
    Step 4 - Select plants from BC1, and create a generation of F2 plants via sib-mating; the resulting generation can be denoted BC1F2.
    Step 5 - Select desirable BC1F2 plants showing the recessive condition, and hybridize with the recurrent parent; the resulting generation is denoted BC2.
    Step 6 - Select plants from BC2, and create an F2 population via sib-mating; denote the resulting generation BC2F2.
    Step 7 - Select plants showing the recessive condition from the BC2F2 generation, and hybridize to the recurrent parent; the resulting generation is denoted BC3.
    Step 8 - Grow out BC3, select and sib-mate the most ideal candidates to create an F2 population, where plants showing the recessive condition are then selected and used as a basis for a new inbred, or open-pollinated, seed line.
    This new generation created from the F2 is a population that consists of, on average, ~93.7% of genes from the recurrent parent, and only ~6.3% of genes leftover from the donor parent. Most importantly, one should note that since only homozygous-recessives were chosen for mating in the BC3F2 generation, the entire resulting BC3F3 generation is homozygous for the recessive trait, and breeds true for this recessive