First, you will select the desirable plants that have the traits that you like, and create an F2 population of them through full sib-mating. You will then select the plants showing your desired trait, which is within the F2 population, and then hybridize this plant with the recurrent parent… this will create a BC1 population.
Next, you will select plants from the BC1 population and create a generation of F2 plants through sib-mating; which will result in the generation known as BC1F2. You will then select plants showing the recessive trait within the BC1F2 generation and hybridize that plant with the recurrent parent, which will create the BC3 generation.
With the BC3, these will be grown out, then select and sib-mate the ideal applicants for the recessive traits that you like, and use them for inbreeding, or open pollination. The F2 generation has on average about 93.7% of the genes from the recurrent parent and only about 6.3% of the genes from the donor parent.
It is good to know that when you are backcrossing to incorporate a recessive trait is that only homozygous-recessives are chosen for the mating within the BC3F2 generation, resulting in the BC3F3 generation being homozygous for this recessive trait and breeds true for this recessive trait.
Backcrossed derived lines are expected to be well-adapted to the environment in which they will be grown and this method of breeding is often used by growers who grow indoors. The downside of backcrossing is when the recurrent parent is not very true-breeding and results in generations that are segregated with the many traits that are deemed desirable but fail to be reproduced consistently.
Another limitation is that the ‘enhanced’ variety differs only slightly from the recurrent parent, with usually only a one-trait difference. If multiple traits are being selected and introduced into a new population, other techniques like inbreeding or recurrent selection will be more worthwhile.
Selfing Cannabis via Breeding
“Selfing” is the process of creating a seed by fertilizing a plant with pollen obtained from itself. The result of selfing is a population that is derived from one parent, known as S1 then every generation after is S2, S3, etc.
With selfing plants, their traits remain the same upon selfing. The plants’ traits are homozygous and will remain homozygous when selfing, whereas a heterozygous plant will show differently and may reveal the unique appearance of these characteristics.
Each selfed generation leads to an increase in characteristics by 50%. Repeated selfing or single-seed descent is the fastest way to achieve homozygosity with a group or family.
With plants grown from selfed populations, there is a better probability of finding self-progeny of all desired traits within a plant. Single-seed descent is a plant that is self-fertilized and the resulting seeds are collected.
Each plant is selfed, generation after generation, without any other plants other than itself, and after six generations of selfing (S6) 98.44% of the genes are homozygous.
Recurrent selection is designed to concentrate the favorable genes by repeated cycles of selection for favorable traits so the first step is to identify superior genotypes for the trait that you are selecting.
Next, inter-mate the genotypes and then select the improved offspring then you repeat these two (2) steps over several generations. Pedigree selection is individual plants that are selected in segregating generations from a cross based on desirability or pedigree.
Ploidy Breeding
Cannabis plants by nature are diploids with twenty (20) chromosomes. At meiosis, each one of the parents contributes ten (10) chromosomes to the zygote that they have formed. Cannabis cells may also be haploid (which is having 1 copy of each chromosome set) as in gametes or diploid (2 chromosome sets per cell).
Mutagenesis
If there is no variation for the traits that you are looking for or cannot be found within other populations, it is theoretically possible to induce variation to seeds and tissues to radiation, alkylating agents, or other mutagens such as colchicine or Ethyl Methyl Sulfonate (EMS).
These things will make changes to the DNA and result in desirable traits to show, though you have no control over what changes with the plant’s DNA. Applying any of these agents does not increase the potency of the plant but merely changes its plant structure.
These mutagens can destroy genes along with chromosomes; these are then passed on to future generations when they are bred. Inducing variability is not the best option, at least for the grower who is a hobby breeder.
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