Image by Mel Frank

The first time I really considered the problem of genetic diversity in commercial cannabis was in a policy discussion about some important goals for the cannabis community and industry. Among the proposed goals was something like “promote and enhance the genetic diversity of cannabis and avoid monoculture.”

A monoculture is a crop of a single type that is grown in a large area. In its most extreme form, a monoculture crop is not only of a single type (such as corn or potatoes) but is also substantially the same at the genetic level (such as all of the crop being russet potatoes or a certain variety of corn).

Before we get into the proposed goal of genetic diversity in cannabis, let’s examine monocultures. First, what is good about monoculturing?

The farmer has a very uniform crop that has been bred to be highly productive and predictable in how it’s farmed. Many things about agriculture are unpredictable—two big things being weather and market prices at harvest time—so it’s understandable that farmers want some predictability going into a growing season.

The limitation of a monoculture is that it’s a total commitment to one strategy. If a new virus or other pathogen reaches a monoculture crop that is susceptible to it, the entire crop is uniformly susceptible and can be wiped out. We are all living through the emergence of a new virus, so we know the outbreak of a new pathogen is something that really can happen. If our human population were a genetic monoculture highly susceptible to the new coronavirus, everyone would need to be in an intensive care unit. Fortunately, for every person who needs advanced treatment, there are many more who show no symptoms when infected; and others are somewhere between these extremes. This dynamic can also exist with crops—a genetic monoculture that is susceptible will be affected uniformly by a new pathogen, while a genetically diverse farm will have a more robust and varied response.

Historic examples of this problem include the Irish Potato Famine in the 19th Century, the “Panama disease” wipeout of the Gros Michel banana variety in the 1950s, and the southern corn leaf blight of 1970. In these cases, monocultured crops had no resistance to new pathogens, which spread widely and caused massive crop failures.

Another downfall of repeated monoculturing is its effect on the land and nearby habitat. Each crop has its own interaction with the soil and the organisms around it. In a sense, each crop takes something from the soil and some crops put something back into it. If, year after year, all the “taking” is of the same kind, then whatever is continuously taken can be depleted. This is a common problem of nitrogen-depleting crops that traditionally were rotated, in a given space, with nitrogen-replacing crops the following season. Nitrogen is essential for things like photosynthesis, protein production, and other vital aspects of plant health and productivity. In the absence of effective crop rotation, the soil can become critically low in nitrogen and unsuitable for farming.

In addition, the monoculture can affect nearby populations of insects, wildlife, soil microbes, etc. Some will thrive from positive interactions with the monoculture—to the point of a population explosion or other form of overgrowth—while others will dwindle because they do not interact well with that particular crop. The net effect is that a prolonged monoculture almost inevitably distorts the environment around it. For example, an analysis of more than 450 data sets and more than 50 insect species demonstrated that “variance in plant nutritive traits substantially reduces [insect] performance” and “increased [diversity] within agricultural crops could contribute to the sustainable control of insect pests in agroecosystems,” according to William C. Wetzel, lead author of the paper “Variability in plant nutrients reduces insect herbivore performance” published in the journal Nature in 2016.

How do farmers address these challenges so they can enjoy the benefits of a monoculture without the negative effects? Generally, they restore whatever the monoculture depletes with fertilizers or other supplements. They avoid the total wipeout from a pathogen or pest with pesticides or other chemicals created to prevent various kinds of pathologies.

Monoculture crops and those with little genetic diversity are more susceptible to pests and disease.
Photo by Whitney Cranshaw, Colorado State University, Bugwood.org

The Founder Effect and Erroneous Assumptions

Back to the policy meeting. As we were discussing the need for biodiversity in cannabis, I pointed out the numerous varieties that are commercially available. I made the point that I have never seen a restaurant offering flights of different varieties of corn; however, when I go into a dispensary, I certainly see a wide selection of cannabis choices. While that is true, it is not the whole story.

Even though there are many different cannabis varieties, most of those that are commercially available have been developed from a relatively limited number of ancestors. When a large number of individuals all descend from a small number of ancestors, this is referred to as the “Founder Effect.”

Here is an easy way to visualize the Founder Effect: Think of the castaways stranded on Gilligan’s Island. Suppose the island had been very large with abundant resources, the castaways never left, and no one else ever came to the island. Instead, the original seven inhabitants had children, their children had children, and so on.

Many generations later, there could be millions of people on the island. But all those people would have the same ancestors. No matter how many branches in any family tree, the entire population of millions of people still would have no more genetic diversity than the original seven people, unless an occasional mutation occurred and was passed on to subsequent generations.

This example demonstrates the error in my thinking—assuming that, because there is a large number of individuals (or cannabis varieties), this means that there is proportionally great diversity within that large number. When a Founder Effect exists, that assumption is not accurate; and the Founder Effect is definitely present in most commercial cannabis.

This makes sense because prohibition limited what was available for people to breed with, and the desire for a certain effect was what people were breeding for. This is why most varieties of cannabis are dominated by THC and myrcene. Varieties with low THC or those with other terpenes present certainly exist; but such varieties are nowhere near as common, and they are more difficult to develop from the readily available gene pool. It may also explain why certain kinds of pathogens seem to pose problems for many or most varieties of cannabis—resistance genes that may exist in a wider gene pool are rare or absent due to the Founder Effect.

A potato field. A monoculture crop, in its most extreme form, is not only of a single type (such as potato) but is also substantially the same at the genetic level (such as all of the crop being russet potatoes).
es0lex | Adobe Stock

What we have in currently available cannabis varieties is a wonderful—but narrow—slice of a very large pie, genetically and chemically speaking. The genus Cannabis has the genetic potential to do so many things that we are not fully enjoying yet. For example, everyone knows about THC and CBD, and we may have heard some things about “minor” cannabinoids like CBG, THCV or others.

But it is still relatively difficult to find a cannabis variety in which something other than THC or CBD is the dominant cannabinoid, even though the genus has the capacity to make dozens or even perhaps hundreds of others. And it is still a relatively unusual variety that is low in myrcene and high in some other terpenes with different effects. When measured by cannabinoids or terpenes, currently available cannabis is far less diverse than it could be, which makes it more susceptible to diseases and pests.

Sources of Genetic Diversity

The future of the cannabis industry and of plant medicine lies in the rich diversity that exists in the many sources of genetics outside the Founder Effect. This is available in the seed collections gathered by some of the giants of our community, not all of whom are famous or yet recognized for their work. It is also available in landraces that exist all over the world. Renowned cannabis researcher and CBT contributor Robert Clarke described landraces as “varieties maintained by local farmers in concert with the natural selective pressures of the local environment. [They were] usually selected for a particular end use, whether it was for marijuana or for hemp seeds or hemp fiber,” in the 2016 article “Cannabis Conversations” published on ProjectCBD.org.

These seed collections, and the landraces or landrace hybrids that many of them contain, are sources of greater genetic diversity that represent a major value to the cannabis community, the cannabis industry, and the world as a whole.

In many cases, based on my conversations, they are eager to share the rich diversity within their collections. What they want and deserve is acknowledgment, some fair form of compensation for their life’s work and contributions, and a say in how their collections are used. By sharing their collections, they can promote diversity in cannabis and contribute to the development of new plant medicines.

Standing on Others’ Shoulders

Just as today’s plant breeders stand on the shoulders of the giants who came before, the seed collectors and other pioneers of our community stand on other shoulders—the communities of farmers and consumers of cannabis plants around the world; the many places and peoples from which came the various landraces. When we define an indigenous cannabis variety as a landrace, that can seem to imply something that naturally evolved and to which no person has a claim of ownership. This was also how many people thought of plant medicines found in rainforests or gleaned from the ancestral knowledge of indigenous peoples. The discipline of ethnobotany explores the traditional knowledge and customs of a people concerning plants and their medical, religious, or other uses. Ethnobotanists have studied and documented these practices, and that work has led to important advances in medicine.

As ethnobotany and other disciplines brought traditional knowledge and medicines into streams of global commerce, some of these medicines created value and intellectual property for pharmaceutical companies. Correspondingly, a new public awareness developed as to the ethics of this kind of value-creation. This was most fully codified in the Nagoya Protocol, which is part of the larger Convention on Biological Diversity. It is an important framework to ensure that—where value is created from local sources and/or traditional knowledge—a fair amount of that value ends up back at the source.

Thanks to the great genetic diversity available from landraces and private seed collections, the coming decades will bring major advances in plant medicines, according to Dr. Ethan Russo, who has been involved researching and developing medicines from cannabis and the effects of the endocannabinoid system in many capacities for decades. This genetic diversity will also bring into the available gene pool better resistance to pathogens and better overall agronomic properties. The global reach and significance of these advances will depend upon taking full advantage of the vast genetic potential and traditional knowledge that are available. This will overcome the genetic bottleneck of the Founder Effect, to the benefit of patients, users, and growers everywhere. And, if handled ethically, there will be significant collateral benefits to independent plant breeders and local communities worldwide.

Dr. Dale Hunt is the founder of Plant & Planet Law Firm, where he practices IP law in cannabis, agriculture, medicine, other life sciences. He also has a doctorate in molecular biology and a bachelor’s degree in botany.