Growers Network Staff

November 12, 2018 4 min read
November 12, 2018
4 min read

An Introduction to Basic Breeding and Genetics

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In this article, Growers Network discusses 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 following is an article produced by a contributing author. Growers Network does not endorse nor evaluate the claims of our contributors, nor do they influence our editorial process. We thank our contributors for their time and effort so we can continue our exclusive Growers Spotlight service.


Genetics


Genetics is the study of heredity in organisms, and how traits are inherited. (1) While this definition is simple, it is 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


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. Female lions with male tigers 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:

  1. Cannabis sativa (C. sativa)
  2. Cannabis indica (C. indica)
  3. 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)

Additionally, there are large variations within these subspecies because of what the cultivation community has collectively referred to as “strains.” In most horticultural parlance, strains are referred to as “cultivars,” or genetically stable cultivated variations.

You can crossbreed strains as well as subspecies, so give it a whirl!


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.

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

In animals, polyploidy often results in premature death or debilitating conditions. However, polyploidy in plants can make 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.

Polyploidy can be used to induce infertility in plants, because odd numbered sets of chromosomes (3n, 5n, 7n, etc) have difficulty reproducing. Polyploidy can also work in the opposite direction as well.

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 for humans. 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.

Editor’s Note: Also, transgenic organisms are not inherently dangerous. The cats in the image above had fluorescent proteins added to their genome, but were otherwise normal cats.



Do you have any questions or comments?

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References and Resources:

  1. (1) What is genetics?
  2. (2) Selective Breeding or Artificial Selection
  3. (3) Polyploidy in Cannabis
  4. (4) Colchicine for humans
  5. (5) Experiments in Polyploidy in Marijuana
  6. (6) Why we’re so scared of GMOs
  7. (7) Unraveling the genetic basis of hybrid vigor
  8. (8) What are the differences between C. indica and C. sativa?
  9. (9) The Return of Ruderalis
  10. (10) Production and Fertility of Hexaploid Primary Triticales
  11. (11) Difference between Cannabis sativa, indica, and ruderalis.
  12. (12) Indica vs. Sativa: Understanding Differences
  13. (13) The draft genome and transcriptome of Cannabis sativa
  14. (14) More on auto-flowering strains
  15. (15) What is Cannabis ruderalis?
  16. (16) The canine genome
  17. Resource: Colchicine
  18. Resource: Polyploidy in Plants
  19. Resource: Transgenes

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