Dude, What Happened To My Clone?
Genetic Drift And Cloning
By: Paul Josephs
Breeder Jones won the Cannabis Cup in Denver for the best mostly-sativa strain! Accolades come from far and wide, and Mr. Jones is profoundly gratified that his breeding and growing skills merged perfectly. Demand for clones of his winning plant is sky-high and he forges a business agreement with a company that will exclusively propagate and distribute his winning cultivar from their large growing facility at a very nice profit to him. After a year, however, he starts getting reports from the distributor that they are getting complaints that the clones they are selling are ‘not the real deal.’ What is going on?
Oh, no! It’s genetic drift!
Internet forums start buzzing with reports that his clones are experiencing genetic drift; bloggers claim the clones are ‘tired’ from over-cloning, or that it is not natural for an annual plant to be artificially prolonged by cloning. All sorts of theories pop up — transcription errors, mutations, rip-offs, you name it. It is the Internet, after all. After personally examining some of the plants in question, it is obvious to Mr. Jones that something is happening here but he doesn’t know what it is, to paraphrase St. Bob of Dylan. The clones are not just like the mother plant that he still has. Maybe there is something to this genetic drift idea.
Right concept, wrong name
There is something happening to the clones over time, and the term ‘genetic drift’ seems apt. The clones seem to ‘drift’ away from their genetic mother plant as far as the phenotype is concerned. But the term ‘genetic drift’ is already in use for a different genetic phenomenon. Genetic drift is a term which describes a change in the genetic makeup of a population over time due to random sampling. This trend has to do with sexual reproduction in a population affected by chance, not the asexual reproduction that clones represent. So what causes this ‘drift’ seen by so many of us?
Mutation is not driving this observable change. Mutations are sudden, random changes to an organism’s DNA. Since we are dealing with a population of independent clones that have genetically identical DNA, a mutation would only affect an individual and that plant’s offspring. Mutations occur and have been documented in Cannabis clones. However, this is not what’s happening with the clones as there are widespread, varying subtle differences between the clones and the mother plant.
Over-cloning, Transcription Errors and the Lifespan Theory
Cannabis is an annual herb which, in nature, depends upon its seeds to sprout the next generation of plants. Some people theorize that it is somehow unnatural and stressful to keep cloning a plant over and over. It seems plausible that there might be small errors that might accumulate in the DNA over many iterations of cloning.
If the plant is normally an annual, might it somehow become ‘tired’ of living many years past its normal lifespan? Not likely. There is no genetic timer ticking away that signals the plant to die after a certain period of time, with the exception of auto-flowering Cannabis plants. It is environmental change, particularly the photoperiod, which triggers flowering and the ultimate death of the plants. Clones growing in an 18- to 24-hour day will just keep growing; cells will divide and differentiate indefinitely. Even a flowering plant can revert back to vegetative growth by switching from the flowering photoperiod back to a long day. There is no genetic time-bomb to worry about. So what is going on?
What could be happening is phenotypic plasticity. This is the phenomenon of genetically identical organisms, in this case the cup-winning mother plant and its clones, changing appearance and properties without the actual DNA being altered in response to the environment the organisms develop in. This is an example of epigenetic change. Epigenetics, as a process, governs the expression or repression of traits in response to the environment. While the actual DNA does not get altered, the expression or repression of traits can change.
A good example of an epigenetic change is taking two clones from a mother plant and putting them in two quite different environments. One is put in a shady forest at sea level on the Oregon coast, subjected to abundant moisture and mild temperatures. The other is put in a mountain meadow at 8,000 feet above sea level in Colorado, subject to high winds, low humidity and cold nighttime temperatures. Being raised in such different environments is going to create a unique appearance for each plant as well as differences in quality and quantity of their harvests. Instead of using the term genetic drift to describe this process, it is more accurate to call it phenotypic plasticity.
Another very real possibility to explain many cases of these observed changes in clones over time is what is referred to in horticultural science as clonal degeneration. Though there is no evidence to support the belief that the process of cloning somehow causes plants to wind down over time, the techniques involved in making cuttings present opportunities for a variety of plant pathogens to infect the clones. Viruses, bacteria and other pathogens can enter plants by insects, cutting tools, and other means. Though not necessarily fatal, accumulations of these organisms will, over time, affect the plant’s overall health and subsequently alter its appearance and qualities.
It follows that if we cloned the two plants mentioned above and again swapped locations, the clones would again change in appearance and environmentally-dependent properties. The Oregon clone would change in the Colorado environment to resemble the Colorado form and vice versa. However, not all changes that occur epigenetically are reversible. Some may persist and be expressed not only in subsequent clones, but also in offspring from sexual reproduction.
Is it a waste of time to grow a clone from an incredible plant if it might not be the same grown in your conditions? Not necessarily. If you are growing the same way as the originator — the same lights, nutrients, temperatures, etc. — there should be only the slightest differences between your clone and the original. On the other hand, if the cup winner was grown outdoors in a particular soil and you are growing a clone of it indoors with your own soil mix, it should be expected that there is going to be a distinct difference between the two plants.
In respect to pathogens and clonal degeneration, time-honored sanitary practices are paramount in preventing or minimizing the opportunity for infection. Soaking cutting tools in a supersaturated solution of trisodium phosphate will kill pathogens, and flaming cutting tools between cuts is a highly recommended practice. Clean growing areas and equipment is a hallmark of a good grower.
If you grow a clone in an ideal environment that really suits its genetic potential, you just might develop an individual superior to the original. Even if you don’t have the same environment and the plant doesn’t perform as hoped for, that doesn’t preclude the value of the clone for your breeding purposes. Assuming some big change has not become a permanent inheritable trait due to epigenetics — a reasonable assumption — the clone’s genome, or actual DNA, is still quite valuable to a breeder. So, buck up, Mr. Jones. Just think of the clones as Highway 61 Revisited.