The Pros and Cons of Selfing Cannabis Plants

Selfing cannabis plants can be a useful technique for breeders, but it comes with some drawbacks. One of the major downsides is the loss of the male portion of the population, which makes future crosses challenging. This article will discuss the misconceptions about selfing, the two basic models of selfing, and the implications for breeding cannabis plants.

Misconceptions About Selfing​

Some breeders believe that selfing a cannabis plant will produce offspring that are identical to the parent. However, this is only true if the parent plant is true breeding for all the traits of interest. If the parent plant is not true breeding, the offspring will show two phenotypes for every trait that is not true breeding.

Homozygous Selfing Model​

The first model for selfing a cannabis plant is when the plant is homozygous for a particular trait, such as pineapple flavor, which is controlled by the recessive gene pp. When a homozygous plant is selfed, the resulting cross (S1) will produce offspring with 100% pineapple-flavored females but no matching males. This model is represented as follows:

S1 cross = pp x pp = pp + pp + pp + pp

Heterozygous Selfing Model​

The second model is when the plant is heterozygous dominant for the trait in question. If the plant is heterozygous dominant for pineapple flavor, the S1 cross will be:

S1 cross = Pp x Pp = PP + Pp + Pp + pp

In this situation, only 75% of the offspring will have pineapple flavor, and the frequency of the P gene will be 50%. This represents a 1:2:1 Mendelian ratio and is quite different from achieving true breeding.

Implications for Breeding​

The process of selfing, especially in the heterozygous model, is similar to half-sib crosses involving regular inbreeding or backcrossing. To achieve something close to true breeding, it will take several generations. However, it's important to note that using the original parent (P1) in the crosses will never result in a true breeding population, even through selfing.

Conclusion​

While selfing cannabis plants can be beneficial in certain situations, it's essential to understand the limitations and implications of this technique. Breeders must consider the loss of male plants and the challenges of achieving true breeding when deciding whether to use selfing in their cannabis breeding plans.