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 their
Inbreeding depression is a reduction in vigor (or any other character) due to prolonged inbreeding. This can manifest as a reduction in potency or a decrease in yield or rate of growth. Progress of depression is dependent, in part, on the breeding system of the crop. Earlier, when we discussed dioecy, we said cannabis is an out-crossing or cross-pollinating species. Cross-pollinated crops usually exhibit a higher degree of inbreeding depression when "selfed," or inbred, than do selfing crops. For example, tomato (an inbreeding or selfing species) can be selled for 20 generations with no apparent loss in vigor or yield, whereas some experiments have shown that the yield of corn per acre is decreased quite dramatically when inbred for 20 generations.
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.
Inbreeding is nothing more than crossing a group, family, or variety of plants within themselves with no additions of genetic material from an outside or unrelated population. The most severe form of inbreeding is the self-cross, in which only one individual’s genetic material forms the basis of subsequent generations. Ml
In cross-pollinated crops, deleterious genes remain hidden within populations, and the negative attributes of these recessive traits can be revealed or unmasked via continual inbreeding. Inbreeding depression can be apparent in S! populations after a single generation of self-fertilization. When breeding cannabis using small populations, as is often the case with continual 1:1 mating schemes, inbreeding depression typically becomes apparent within three to six generations. To deal with this problem, breeders often maintain separate parallel breeding lines, each of which are selected for similar or identical sets of traits. After generations of inbreeding, when each of the inbred lines, or selfed populations, begin to show inbreeding depression, they are hybridized or out-crossed to each other to restore vigor and eliminate inbreeding depression while preserving the genetic stability of the traits under selection.
The donor parent is chosen based on a trait of
The vast majority ol texts written to date on the subject of breeding cannabis have espoused
Many breeders will backcross with one of the original parents. It is not necessary to backcross to get stable plants—selective breeding will do this over time. However, backcrossing can speed up the stabilization process and reinforce preferred dominant characteristics.
Desirable dominant traits can be isolated and undesirable traits are gradually eliminated. Unstable parent stock risks producing heterozygous offspring. There is a risk of greater variation, and undesirable, unpredictable traits can emerge.
The quantity of plants bred from a particular strain can also affect stabilization as well. There is a greater chance of “throwbacks” to earlier strains if there has been a lot of crossbreeding performed in the plant’s history.
STABILITY & BACKCROSSING
Unwanted alleles that can negatively impact a strain are more likely to be passed on when both parents are carriers. When undesirable characteristics are passed on by both parents, the recessive characteristics become dominant and will be passed on to all subsequent offspring.
The vicissitudes of plant genetics can be seen when driving past any modern food crop. Fields of heavily hybridized and inbred cereal crops, for example, will generally be homogeneous. However, there will always be some freaks that stand out from the crowd.
The same occurs with marijuana. A batch of stable hybrid seeds can produce a plant resembling a grandparent or original landrace, the same way a redhead might happen here and there in a family with very few redheads in their genealogy. This is rare and can be an inconvenience or a boon.
Without genetic assays that can give precise information about the plant’s characteristics, experience plays a big part. Growers rely on look, growth pattern, leaf shape, color, and potency for desired new strains. They select a number of plants for breeding from the same seed batch that have similar characteristics. These plants are interbred, and the plants that resemble the desired strain are bred together again.