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Cannabis Genetics 101.2

Posted on June 1, 2003

The Hawaii Project

Dr. Dave West

Dr. Dave West

“OK” Brian said after the first lecture, “I’ve got genes, alleles, loci, chromosomes and heterzygotes. Can you bring that a little closer to earth? What, for instance, if anything, does that have to do with your project in Hawaii?”

Actually everything. OK. School’s on again. Let’s assume you go back and read the first in this series ’cause you’ve forgotten it all already, and we’ll carry on from there. I left off saying we’d be next looking at one of the truly marvelous inventions of nature, the mechanism responsible for generating all the variation we observe within species. I’m talking about what Darwin referred to as “variation under domestication”. All the different breeds: dogs, cats, pigeons, people and … pot. (The alliteration made me do it.)

Let’s look at what’s happening in the Hawaii project as an illustration. The issue in that case is one of adaptation. What we call “hemp” — or some prefer “industrial hemp” though I think “hemp” is just fine — is a breed of cannabis generally found in the temperate zones of the planet. The plant’s life cycle is driven by a genetically programmed response to the length of the night. Nights in the temperate zone begin to lengthen after summer solstice and the plants shift from vegetative growth — which has resulted in long stems — to reproductive phase, so seed will be set and matured by frost.

In the 20th century, the hemp fiber growers of Wisconsin developed a collaboration with the hemp seed producers of Kentucky by exploiting the photoperiod response in reverse. Here’s how: When you plant seeds of Kentucky varieties (meaning varieties adapted to finishing seed in the limits of the Kentucky growing season, approx. 35”) in Wisconsin (45”) the plants stay vegetative longer, the reverse of what happens when you move varieties south of their zone of adaptation. If you are after fiber, you want the plants to remain vegetative as long as possible (more vertically elongating stem). So Kentucky produced the seed that Wisconsin planted for fiber. This collaboration lasted until 1957, the last year hemp was planted in Wisconsin. This is the only case I’m aware of where specialized industries developed to harness this feature of the plant in order to maximize productivity.

Now, if you take plants with that genetic program from temperate 45 degrees to tropical 20 degrees, where the days and nights are about equal in length most of the time, the plants immediately experience long nights characteristic of late season in the north. So immediately the plants fire up their reproductive gear and little vegetative growth occurs. Varieties that would easily reach 9’ in London, Ontario, are only 2’ tall, done growing and setting seed after just 2 months in Hawaii.

Alrighty then! We have two situations. One is the egregious misfortune that the germplasm was lost. Two is that there are no tropically adapted “industrial” varieties of cannabis. These two situations are connected in that they are both a matter of lower latitude adaptation, one lower than the other. The lost germplasm, that of the unique American hemp called “Kentucky Hemp”, was bred to cornbelt latitudes. As I have described in great detail elsewhere, this hemp arose in Kentucky from the meeting of Chinese and European hemps after 1850. Of the European hemps, only the superior Italian hemp was adapted so far south. What this loss means is that American hemp farmers of some hoped-for future will not have proper varieties for their growing regions. There is a gap, a lag, that must be addressed eventually, and that is what I set about to do in Hawaii. The State of Hawaii wanted crop diversification. Both goals involve the introduction of cannabis with differing photoperiod adaptations. How do we proceed?

If you look across the globe, there are cannabis plants that do grow abundantly in the tropics. So the photoperiod adaptation of those plants needs to be combined with the internode elongation and fiber or seed characteristics of “industrial” cannabis. The plant’s architecture must be modified and its growth habit altered. We want to bring in the “agronomic” qualities that “industrial” varieties exhibit, such as tolerance to dense planting. An obvious focus of concern to some is the coincidence of high THC production with short-day photoperiod adaptation. This is a complicated situation because it takes years to create new plant varieties. One must ask, will THC still be a big issue in 10 years? After all, the whole issue of THC in hemp varieties is political. THC never used to matter in hemp. It’s a made-up issue. It is as informed by science as were the tribunals of the Inquisition. So, that means a new wind in Congress could sunder years of investment in lowering THC to absurd levels. Looking at the rapid changes taking place everywhere but the US, I can imagine there might come a day when someone will ask, astounded, “You mean you bred the THC out of the plant?!”

So, without going off on too much of a tangent, whatever happens next, the first step is the same: identify genetic sources of the traits of interest; cross them; select within the variation that emerges. The photos accompanying this article illustrate the range of variation released when you do that. These plants all had the same grandmother. They are all descended from seed born on a single female plant. As for Gran’pere, well… Gramma mixed it up a bit, had international affairs.

2 foot plant 4 foot plant 6 foot plant 8 foot plant
2 foot plant 4 foot plant 6 foot plant 8 foot plant

After the initial critical cross was obtained and a large progeny harvested, the next step was to recombine the population. Because this is an agronomic (as opposed to horticultural) breeding program, pressure (artificial as opposed to natural selection) is applied to the population to urge it in the direction of agronomic traits. For instance, we are interested in plants that have achieved 8 feet of growth and are still vegetative after 3 months, as with the individual in the lower left photo [see 8 foot plant]. Her cousin [see 2 foot plant] went reproductive very quickly and never got taller than 2’, but it is setting seed. There could well be circumstances where the short-quick seed producer might be the preferred type. (Jargon alert: we say “phenotype” for the manifest characteristics of the plant. The genetic underlayment is referred to as “genotype.” This will be on the test…) In the photos on the right [see 4 foot and 6 foot plant] are two individuals intermediate between the extremes on the left [see 2 foot and 8 foot plant], at 4 and 6 feet of growth in the same 3 months. The characteristic height would be said to exhibit continuous variation.

Pressure is applied by biasing the contribution of gametes from individuals in the population. Example: we had an insect pest identified as the Chinese Rose Beetle. It really chomped down on some of the plants. Yet other plants were left alone. There are two possibilities: that the beetle is leaving the plants alone because there’s something it doesn’t like about them, they taste bad; or, that some plants lucked out, they escaped. If “taste bad=TRUE”, then there is a genetic basis to the health of the uneaten plants and choosing those plants (removing the affected ones before their pollen [male gamete] is shed) will improve the population. However, if “escape=TRUE”, then selection won’t do any good. So we hope the first hypothesis is true, make selections accordingly as humans have done in the course of domesticating plants and animals over the millennia, and wait with anticipation the next cycle to see if we were effective. Selection is applied to the population, so the character of the plants is gradually, over successive cycles, morphed toward the desired type. The biological stuff is wonderfully plastic this way. But the effectiveness of selection depends on there being a link between the phenotype and genotype. The tighter that link, the more effective will be the selection. It’s a wysiwyg (what you see is what you get) situation. But if there’s a lot of noise in the system — in this case escapees, not taste-bads — then the breeder will be less effective in recovering in the next generation the trait he selected, and we will find the happy beetles feasting again next cycle on unlucky individuals.

So now we’ve generated a population of individuals among which we can select for those that combine the desired traits. And that population has been through a round of recombination. What does that mean? Oops, there’s the bell.

Related article

Cannabis Genetics 101
February, 2003

Copyright © 2003, Cannabis Health. All rights reserved.

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