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Breed Plants with the Best Traits

December 6, 2016

When growing cannabis, it’s easy to get inundated with lots of scientific jargon and insider terminologies. We talk about indicas, sativas, cannabinoid ratios and terpenes, but how do all of these aspects factor into the seemingly random nature of breeding?

Where THC and CBD come from

For our examples, we’ll focus on the two most prominent cannabinoids, THC and CBD. These two compounds are the most prized and therefore the most valuable, and each has its own advantages and disadvantages for consumers and patients.

The plant’s DNA produces different types of proteins or enzymes; THC and CBD are in turn produced by one particular type of protein (called “synthase”). Strains that produce higher amounts of THC (such as Durban Poison or Blue Dream) do so because they contain many genes for the THC synthase protein, whereas strains with higher amounts of CBD contain many genes for the CBD synthase protein. Higher THC strains don’t usually make a lot of CBD, since the relationship between THC genes and CBD genes is inversely proportional. In other words, the more THC your plant produces, the less CBD it’ll produce (and vice versa).

The additional THC (or CBD) genes for a high-level strain come from a process called gene duplication, or repeating the genes in the DNA. This is a somewhat random phenomenon that may be responsible for most new genes seen throughout natural history. A plant like cannabis is especially prone to a lot of repeated genes, simply because it can handle them.

How to control gene duplication

Trying to control genes can be tricky business. We’re talking about tweaking individual molecules at the DNA level. It’s much easier to take advantage of natural processes, which is precisely what breeders do.

Imagine that we want to breed our very own 1:1 THC:CBD plant for medical patients. To do this, we simply take a high-THC strain and cross it with a high-CBD strain. We produce only four seeds. By probability alone, we should get four plants with the following traits:

  • One with high THC and low CBD
  • Two with the same level of THC and CBD
  • One with low THC and high CBD

So essentially, we should have two 1:1 plants for every high-THC and every high-CBD plant we grew. After we get our test results back, we can keep those 1:1 genetics by simply inbreeding; that is, we take the 1:1 plants and cross them with each other.

“Mr. Soul,” the moniker of the man who bred the world-famous Cindy 99 strain, recommends a cubing process for breeding out undesirable traits. To cube, he advised cultivators to “breed the ‘son’ of a pollinated mom, then breed the ‘grandson’ with her, and on and on to delete male genetics and preserve the females.” Although this may sound somewhat shocking, plants are accustomed to inbreeding in this fashion, and they’ve evolved in a way that minimizes the negative effects to near-negligible levels.

Within three or four generations of inbreeding the 1:1 plants, we’ll eliminate the high-THC and high-CBD cultivars. We’ve got a new strain that consistently produces 1:1 plants.

Breeding for other traits

The process we’ve just described works similarly for making strains that consistently produce high-THC or high-CBD plants. We find the ones with the traits we want, inbreed them, then keep the new genetics. For instance, if we want high-CBD plants, we cross the high-CBD cultivars with one another until we get rid of any high-THC or 1:1 plants. And so on and so forth.

Other traits like high yield, short stalks or purple flowers may also follow be inherited from genetic cultivars. So, keep careful, detailed notes of your grows. Record how many plants bear the traits you want, and cross them with one another.

Unfortunately, this model works only for certain types of inherited genes. Many of the traits that businesses want today, such as terpene production and resistance to pests, drought and so on, may not be inheritable. Much of this is still being figured out by plant geneticists and computational biologists.

The future of cannabis breeding

Currently, several laboratories in the U.S. are constructing genome maps for Cannabis sativa. We’ve long had the DNA sequence for cannabis, but we don’t yet have the genetic map. A map will tell us where the genes are located on the DNA sequence. This is important, because until we have this map, most of our breeding procedures are just guesswork. We’re relying on trial and error to breed the traits we want, which means wasted seeds and wasted resources.

But with a genetic map, we’ll know which cultivars to cross to get the traits we want—and we’ll keep those traits in the lineage.

“In the 18 years of my career in computational biology,” said Syngenta’s Keith Allen, speaking during October’s CannaGrow Expo in Denver, “I haven’t seen a field advance in genetic understanding as quickly as I have with the cannabis plant.”

Biotechnology and cannabis

All this brings up the question: What about genetic engineering? There are rumors in our community that big agricultural biotech companies want to take over the cannabis industry. Although that may be the case one day, smaller cultivators should be safe for now.

Our genes of interest, namely those for THC and CBD synthase proteins, are too big for biotechnologists to work with. For scientists to directly insert or transfer genes from one plant to another, they need a vector, which is a microorganism that can store and transfer the gene. As of this writing, scientists use bacteria, viruses or yeast as vectors. But the genes for THC and CBD synthase proteins can’t fit in these vectors.

So, only traditional breeding methods (that is, pollination) can tweak THC or CBD genotypes. All the fancy technology in the world can’t compete with time-tested cannabis farming methods—for now.

By Randy Robinson
Cannabis Cultivation Today articles are for informational purposes only and should not be considered legal guidance or advice on grow practices. You should contact an attorney or a qualified cultivation consultant for specific compliance and cultivation advice.
© 2016 CAN Performance Group, LLC. All rights reserved.

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