A brief overs-simplified description of plant breeding for the non-specialist
When driving past vast fields of purple or yellow this time of the year, do you ever wonder where those flax or canola plants “came from”? Why do planted fields look so uniform compared to, say, a ditch, a meadow, or your crazy neighbour’s “natural” mow-free lawn?
While a farmer could indeed cultivate any random plant in the field, there might not be much point if they serve no purpose. The crops you see in commercial production are actually specific variations of what you might find in a meadow, but have been specifically guided to grow very well in that environment while providing very useful things for food and industrial use. That deliberate effort using time, money and effort is plant breeding.
A nice succinct definition of plant breeding is “science of maximizing plants’ positive genetic traits to produce desirable effects.” How did this start? What’s involved?
First, a super basic but fundamental thing to keep in mind: when you go out into nature, each individual plant is slightly unique from the next, due to the way the genetics of its parents were combined together. (My other post using Lego to describe molecular biology fundamentals might be help illustrate some of these concepts). For example, if you look at a row of spruce trees, of course they are all indeed spruce trees, but each one is a bit different from the next. In technical terms, we’d say that row is a “population” of trees, comprised of many individuals. Same can be said for any species you come across, whether it’s in a ditch, in the forest, in a field, etc.
Over time, the unique individuals that are best-suited for the specific place they’re growing will thrive more than the rest, and therefore chances of survival are naturally going to be greater; basically, those less-suited for said environment will not reproduce with the hardiness or vigour (or at all) that the more ideally-suited individuals will. (It could be for any number of reasons, maybe the leaves are bigger, maybe the tree is taller, maybe the roots are deeper – many possible variables that differ for each plant and/or environment). Those characteristics (traits) are the physical way (“phenotype”) in which the individual grows, based on its underlying genetics (“genotype”). Thus, “natural selection” takes place. Think of the environment as a filter thrust upon the population where only the best-suited survive. This has been a naturally-occurring phenomenon as long as plants have been growing, whether a local climate changes surrounding the plant, or whether seeds are somehow dispersed into new environments in different geographies.
So then, if “natural selection” exists, does this imply that “unnatural selection” must also exist? Sort of, but that would be a clumsy label. The alternative to that naturally-occurring ebb and flow of environmental selection pressure and survival of the most fit would be when humans took a more pragmatic approach to the environment in which they found themselves. Maybe “human-directed” is a more fitting term. (On the other hand, are humans not part of the natural world, and thus, human-directed selection is merely a more recent introduction of the environment putting selection pressure on plants and thus, the next phase in that continuum of natural selection? That’s a philosophical debate way outside the scope of this post but interesting, no?) Actually the terms “selective breeding” or “artificial selection” are used to distinguish the human-directed plant breeding efforts from natural selection.
Let’s back up a step for a quick historical perspective, with the dawn of crop cultivation which apparently began about 23,000 years ago next to the Sea of Galilee:
A person would have emerged from his cave and planted a bunch of seeds, and after using his ancient sickle for harvesting,
the harvested seed would be used for food while some would be kept for planting the next season.
Since this was a matter of life or death for the caveman farmer, it would make the most sense to keep seeds from the strongest, healthiest, hardiest plants in the field, and then the rest could be eaten. Selecting the best seeds each season, over time, would mean that genetics from those hardiest or most vigorous individual plants would be planted and re-planted year after year. So, in addition to the natural environment – natural selection – acting as a filter to “weed out” all but the strongest individual plants, the farmer’s survival activities become a second “filter” thrust onto the population of plants (his crop). And thus, human intervention in selecting for plants begins. Let’s distinguish this from “natural selection” as simply, “selection.” Thousands of years ago, this likely wouldn’t have been consciously done for any other reason than the important fact that “STRONGER PLANTS = STRONGER ME! STRONGER ME, MORE BOPPING! MORE PLANTS…MORE FOOD…LESS ME HUNGRY…MORE CAVE PARTY!”
(Disclaimer: any resemblance in this post to any real person is not intentional, and purely coincidental)
Fast forward to today, and now we have an entire career option dedicated to selecting the best plants on behalf of entire industries. Plant breeders are employed by both public and private sectors, are highly educated in their craft, and dedicate years if not decades to this selection process. They must consider the realities of the genetic pool they’re working with, as well as intended growing region, while still making sure to achieve the specific traits that a company or industry is demanding. Decisions have to also account for local or international regulations around breeding to make sure the industry doesn’t run into trade barriers. Of course there are entire breeding teams dedicated to this process as well, as it’s a very demanding, tedious and lengthy process. I worked with one of those teams for a while, and organization, efficiency, and dedication are key for the long haul. Logistics across the growing region can be a massive challenge too, not to mention fending with unpredictable weather and evolving policy or regulation over multiple years. Once the desired, targeted traits are stabilized and reproducible (“fixed”) in a population, it is considered a new “variety,” named, and available on commercial markets to be grown by farmers. Oh, and breeders today mostly don’t look like cavemen either.
Each current-day breeder will have a different approach. Some are classical or traditional breeders, which is a highly educated version of the selection process already described; when classified as such, resulting varieties of this approach are NOT “genetically-modified organisms” (GMOs). Some breeding programs will modify (up-regulate, down-regulate, insert, silence, etc.) existing genes within the plants or use genetic sources derived from a compatible plant, or may introduce genetic sequences from other plants or animals in addition to selecting from populations. These are two sub-categories within the broad category of GMOs (the former is called “transgenic” and the latter “cisgenic”). Some programs will enhance the traditional process using “molecular markers” – small defined genetic sequences, linked to unique, known traits, which enhance speed/efficiency of screening populations. This is called marker-assisted selection (MAS); no modifications other than those resulting from classic breeding techniques result, and rather the MAS are used to identify desired traits early and point back to the parent material.
(MAS isn’t a GMO technique. Here’s an analogy: let’s say you were trying to create a new variation of an old but good soup recipe, so you start with a big pot of the recipe you know is good. Also, you had a bunch of small pots of soup on the stove into which you put a small amount of the main batch (but not emptying the big pot), each to have different spices added. Before arbitrarily deciding which experimental spice regime to be added to the big pot, you’d take a spoon full of each small pot to taste-test. You might keep the tastiest one and throw away the rest. The small bit of soup you tasted doesn’t go back into the small pot, it’s just an indicator to you which one you’re going to select. Then, you’d know exactly the way to improve the big pot of soup – just make the same spice adjustments and voila. In the breeding context, the small pots are the plant population, the sample in the spoon is the marker, your taste buds are the lab equipment used to detect the marker, and the large pot where ingredients come together just right is the plant selected to move forward in the breeding process.)
Although in the past selecting for the best plants would have been a dynamic process on a continuum over decades, with continual improvements seen over time and no particular “finish” to the process, it’s a bit different today. Plant breeding is a highly-regulated process which leads to a defined “plant variety.” As mentioned earlier, it’s narrowed down year after year to a few final contenders of individuals best-suited for whatever the objectives are, until a winner is finally decided upon & named. In Canada, information for that winner is then submitted to the federal government, a rigorous registration process follows, and once it is formally registered with the Variety Registration Office, the variety is then allowed to be sold on the market (or in some cases, it is available for its rights to be bid upon and the winning bidder can then start to sell the new variety). Take a look at all the different varieties available, just in one province in one year alone..! So, the breeding process today is still a continuum of an ever-evolving population, with offshoots leading to these registered variety end points (which may or may not be brought back into a breeding program in the future, to utilize already-optimized genetics for certain traits).
One last note: in their natural environment, a plant breeder will be seen wearing the mandatory plant breeder tilly hat:
Rumor has it that it bequeaths unique powers to the plant breeder to further enhance their selection processes.
Just one more incredible mystery of the natural world.