Growers Network Staff

February 22, 2019 6 min read
February 22, 2019
6 min read

Improving Your Cannabis Yields Via Genetics: A Tutorial

In this Growers Article we discuss how to improve crop yields by taking advantage of some of the principles of genetics, namely artificial selection (also known as selective breeding), crossbreeding, and inducing polyploidy.

The purpose of this Grower’s Article is to educate and inspire growers who may or may not know about genetics options that are available to them that don’t require a genetics laboratory.

To skip to any section within this article, click the links below:

  • Genetics
  • Artificial Selection
  • Crossbreeding
  • Polyploidy
  • Genetically Modified Organisms (GMO’s)
  • Comments

  • Genetics

    Genetics is the study of heredity in organisms, and how traits are inherited. (1) While this definition is simplistic, it effective because genetics covers very broad topics. For our purposes, we want to know how to change a plant’s genetics to improve its yield.



    Artificial Selection

    Natural selection is anything but random.Richard Dawkins

    Artificial selection is the means by which humans can take natural selection into our own hands. We choose the traits we like best in a plant, and only let the plants that have the best of those traits reproduce. Alternatively, you deny reproduction to those with the worst of the traits. (2)

    After several generations of selective breeding this way, permanent changes may start to appear in your crops, depending on the complexity of the trait you are selecting for. This is how crops such as corn (a grass) and bell peppers came to be.

    Farmers and cultivators have been engaging in artificial selection for much longer than we understood how it works. Without it, our staple crops would be much smaller and more difficult to get calories out of.

    That said, let’s look at more modern techniques of improving crop yields, some of which can have fast turnaround times.


    Crossbreeding



    The liger Hercules, the result of a cross between a male lion and a female tiger. Opposite sexes create a tigon.

    Crossbreeding is also an old strategy, but takes significantly more intentional thought and effort. One of the most well-known crossbreeds is a mule, made from crossing a male donkey and a female horse.

    Generally speaking, people try to crossbreed related species because the resulting offspring benefits from what is known as “Hybrid Vigor.(7)” Of relevance to our concerns, however, are the species of Cannabis. There are 3 known species of Cannabis today:

  • Cannabis sativa (C. sativa)
  • Cannabis indica (C. indica)
  • Cannabis ruderalis (C. ruderalis)

    Each species has different characteristics. When comparing them, it’s important to note several factors.

    1. Size: C. Sativa grows to be the tallest of the three. C. ruderalis is the smallest. (11)
    2. Leaf distribution: C. indica’s leaves grow densely-packed, while both C. sativa’s and C. ruderalis’ are more spread out. (11)
    3. Ratio of THC to CBD content: C. indica generally has the highest THC to CBD ratio (12), whereas C. ruderalis has the lowest THC to CBD ratio (not much THC, but plenty of CBD). (8)
    4. Resistance to stressors: C. ruderalis is significantly more resistant to disease and pests than the other two species. (15)
    5. Variation within species: C. Sativa has been cultivated the longest by people, and thus has the most “breeds.” However, because C. ruderalis is closest to a “wild” cannabis plant, it likely has a significant amount of genetic diversity locked away, waiting to be discovered, in the same way that all dog breeds came from gray wolves. (16)
    6. Other differences: C. Ruderalis does not depend on light cycles for flowering. Instead, it flowers based on the age of the plant, termed as “autoflowering.” (13)(14)

  • Hybridization often tends to lead to infertility in the resulting offspring. While this problem cannot be solved in animals, it can be corrected in plants by inducing polyploidy, which we will cover in the next section.



    Polyploidy


    The world’s tallest man in recorded history, Robert Wadlow. While he was not polyploid, gigantism in plants can occur from polyploidy.

    All plants and animals have a certain number of chromosomes. Humans have 46 total chromosomes — half of which comes from our mothers, and the other half from our fathers.

  • Half a set of chromosomes (found in sperm and eggs) is called haploid, abbreviated as (n).
  • A full set of chromosomes is called diploid, abbreviated as (2n).
  • More than (2n) is referred to as polyploidy. (3n) is triploid, (4n) is tetraploid, (5n) is pentaploid, (6n) is hexaploid, etc.

    Polyploidy in plants makes them bigger, hardier, and tougher. (3) Plants experience an effect called the Gigas effect. The greater the number of chromosomes, the stronger the effect. There is a diminishing return, however, as plants become genetically unstable the more times that polyploidy is induced. Additionally, results can vary, as noted in this scholarly article.

    One other application of polyploidy in plants is useful — it can make sterile hybrids fertile again. Triticale (a hybrid of wheat and rye) is notable, because it can be made fertile through polyploidy. (10)

    To induce polyploidy in plants, we need to use a chemical named colchicine. Colchicine is normally used to treat gout in humans (4), and excess exposure to cochicine is considered toxic. In plants, however, it causes polyploidy.



  • Genetically Modified Organisms (GMO’s)

    A brief discussion on the nature of genetically modified organisms.


    Transgenic cats with fluorescent proteins.


    Many people are afraid or concerned about the presence of GMO’s in their food and elsewhere. Unfortunately, this stems from a fundamental misunderstanding of the definition of a GMO (6) and the vagueness of the term GMO.

    A GMO includes any kind of intentional genetic modification to an organism. Inducing polyploidy in plants makes those plants GMOs by definition, although we are not adding any new genes to the plant nor are we changing any existing genes.

    What’s important to recognize is that many people equate GMO’s with transgenic organisms, or organisms that have DNA from a different species altogether. Polyploid plants do not take genes from other species, merely extra copies of their own, preexisting DNA. Thus, they are GMO’s, but not transgenic.



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