At a McKinsey sustainability symposium a few years back, a very eloquent and charismatic partner in the firm made the resounding argument that the future, under climate change, will not look like the past.
For agriculture to continue to function in meeting the world’s need for food, fuel and fiber, we very much rely on the future to look like the past because this consistency in patterns helps to plan and time the growing season. Agriculture emerged in the Holocene, a period of the earth’s history marked by limited variation in climate, if one looks back at climate patterns using a geological time scale. Some scholars argue that it is the relatively stable climate of the Holocene that enabled the emergence of agriculture and the permanent human settlements that followed in many places around the globe. Thanks to the consistent rainfall and climate patterns, early hunter gatherer societies underwent a pattern of plant-rich intensification that enabled the transition to permanent settlements supported by the predictable production of newly domesticated plant species. Today, many thousands of years later, agriculture is the dominant form of land use on the planet.
While farmers have always had to deal with variations in weather patterns in a season and between seasons, extreme swings in rainfall and temperature and the overall less predictable patterns that we can expect under climate change, can wreak havoc on a farmer’s ability to reliably achieve a harvest. Increasing variation in weather patterns is alarming many scholars around the world (read here, here and here for scholarly articles covering this risk), but there is reason to hope as plant breeders can use the plasticity and adaptability of plants to help farmers adapt to a changing climate.
This Field Note will look at how plant breeding helps farmers adapt to climate change and the broad toolkit that plant phenotypic variation, meaning the way in which individual plants differ in the observable characteristics dictated by their genes, can provide to climate adaptation. This article will not cover new tools, like CRISPR-Cas, that breeders can use in developing new plant traits, which will be covered in a separate Field Note.
This article will focus on two questions:
1) Why is plant breeding a massively important tool to help farmers adapt to climate change?
2) How can plant breeders breed climate adaptation into new varieties?
1) What is plant breeding and why do we believe that it will help farmers face the greater variability in climate under climate change.
Some readers may be wondering what plant breeding is. Plant breeding is the scientific discipline that studies how plants species can be adapted to fit human needs. Most people’s caloric needs today are met by plant (and animal) species that have been domesticated. The process of domestication is one where a plant is continually placed under artificial selection (see this excellent article for an explanation of artificial selection) for traits that enable it to be grown under human control, meaning in a farmed or otherwise human managed environment. These traits can be everything from resistance to diseases and pests, which helps plants avoid or grow despite disease pressure, to the characteristics that make fruits and vegetables more appealing, such as color or aroma. Plant breeders study the adaptation of plants to human needs and then identify the improvements and novel solutions that enable plants to continue to evolve to meet the ever-changing needs of the human population. It is, in essence, human directed evolution on an incredibly fast pace.
Climate change presents several serious concerns that farmers will need to manage, both at the level of day-to-day farm management as well as at the level of farm economics, to ensure that farming remains a profitable activity. But there is reason to be hopeful when it comes to adapting plants to a wider range of climatic conditions. This is because it is possible to identify variants within a crop that can grow under different temperature, day-length, and many other climate and weather variables. In fact, it is plants’ incredible plasticity, meaning their ability to adapt to a very wide range of habitats, that plant breeders continually exploit to create new varieties. These new varieties expand the range across which a crop can grow, thereby providing yet more options for farmers to use in identifying a crop that will meet their changing weather conditions. In addition, crop varieties can be moved from one region to another so as regions get drier or wetter, cooler or warmer, one can use the existing library of plant traits to match the right crop with the right environment.
We can look at how much variation we have accumulated in the soybean crop since its introduction in the US, just about one hundred years ago. Soybeans are perhaps the last large scale crop introduction in the US and became part of the core American commodities in the early 1900s. Until around WWII soybeans were adapted to grow only in the southern U.S. Soybeans today are grown from the far north in Saskatchewan all the way to Southern Argentina, a range that spans most of the habitable and farmable land on the planet. Corn, a crop that evolved in Mesoamerica in semi-tropical conditions is now able to be grown across just about the same range, as is possible also for wheat. We can leverage the range across which plants are already adapted to address the new climate scenarios (for example, greater heat or humidity or drought) that may emerge in different locations.
As another example of improving crops’ performance in the face of weather and the increasing intensity of weather events, we can look to one of the most successful and very recent plant trait introductions, which is the development of pod shatter resistant canola. With pod shatter resistant canola, one can straight combine with a grain header rather than needing to use a swather weeks ahead of harvest, as had been done in the past. This trait, introduced broadly only in 2018, allows canola to stand in the field until it is ready to be harvested, a trait which will come in handy in the face of greater variation in weather patterns. It can be expected that under climate change the severity and intensity of storms will increase. This poses a risk to canola that is not shatter resistant as leaving the fragile canola standing in the field would be extremely risky. A storm at the wrong moment could decimate the mature crop by causing the pods to shatter and the canola seeds to be dropped on the ground. The looming threat of storms led farmers to swath the crop to help it mature faster and keep it from shattering by being laid in windrows, which was not an optimal solution as it required an extra field activity, and the windrows were susceptible to wind loss, in particular. Now that the genes for shatter resistant canola have been identified and plant breeders can introduce this trait into new varieties, farmers can leave the canola standing in the field, knowing that it will better handle big storms and strong winds, and harvest it at full maturity, when the quality and yield is at its best.
2) What if climate change presents a new challenge for which new tools are required, beyond the existing adaptations and varieties already developed by plant breeders?
A recent article in Nature Climate Change gives some clues as to the types of tools that plant breeders can wield to enable farmers to adapt to a changing climate.
Researchers out of the CSIRO Breeding Institute in Canberra, Australia have bred wheat seedlings that emerge with long coleoptiles and that they believe could better withstand drought conditions. The coleoptile is the spindly part of the plant that emerges from the seed and that pushes the cotyledons and emergent leaves, up to the soil surface. Breeding for coleoptile length is hardly top of mind for most plant breeders as it is not a characteristic directly related to yield, disease resistance, or other marketable characteristics of a crop. Nonetheless it is a trait that shows variation among wheat plants and is therefore a trait that plant breeders can exploit in a breeding program. The scientists who undertook the study found that seeds with long coleoptiles could be planted deeper in the soil where there is more moisture and hence could better withstand drought conditions at germination. This means that farmers could plant the seeds deeper and that the wheat seeds could still germinate even if the rain did not arrive quite in time or following the regular pattern that one would expect given where the crop is being planted. By exploiting this otherwise overlooked plant trait the scientists could manipulate the crop’s performance in different environmental conditions.
“Great! Problem solved!” you might think. All one needs to do is to breed plants with longer and longer coleoptiles to continue to adapt crops to changing rainfall patterns and drought!
Except, it is not that simple. In the case of drought tolerance at germination, there is not one solution to the problem, rather a different solution needs to be found for each geography where wheat is grown. This is because the temperature of the soil, in this case, makes a big difference to the success of this adaptation to climate change.
To illustrate what is meant by needing multiple solutions to each of the problems, one only has to compare the performance of this innovation in the USA and Australia, both very large wheat producing countries and exporters onto the global market. Both in the US and in Australia, much of the wheat is planted in the months of April and May. However, whereas in Australia farmers are planting into hot ground coming out of their summer, in most parts of the US in the months of April and May, the soils are just emerging from their winter slumber and so the deeper you go, the colder the soil gets. This means that even though there may be more moisture in the soil, seed emergence will be delayed because of the cold which may lead the seed to rot. In the US farmers tend to seed right as the soil thaws out, so planting the seed shallow means giving extra warmth to the seed and support to the roots that are going into cold soil.
For a climate change adapted wheat variety in the US, one might want to pursue other strategies to create drought tolerance: breeding for better soil moisture uptake and/or breeding for plants that go into dormancy when a drought occurs and then respond quickly when the rains return. It is important to remember that each of these options, while improving one set of outcomes, might come with trade-offs that farmers need to navigate in planning the growing season to maximize the chance of achieving a harvest. If plant breeders develop a variety that goes into dormancy following a drought, then the risk could be that without rain the crop would not emerge at all. By contrast, if a farmer had planted a more traditional variety there would at least be some harvest, though of course the yield would be lowered by the lack of water. This last example is meant to illustrate the complexity that farmers need to face when choosing whether to adopt new seed varieties developed by breeding programs.
Despite the many potential tradeoffs, the opportunity is for plant breeders to match a plants’ intrinsic phenotypic plasticity and the natural genetic variation in traits, to the various environments around the world where that crop is grown and to the climate and economic context in which a crop is grown. In a sense, one could argue that breeding specifically for climate change is superfluous. In fact, for corn, it has been shown that breeding for increased yield under varying water availability regimes optimizes the plant’s performance under drought, rather than bringing about a tradeoff between drought tolerance and yield. The study’s authors conclude that the two, better yield and more drought tolerance, go hand in hand which is excellent news for those of us who worry about our agricultural system’s resilience under climate change. By looking holistically at the crop and considering previously overlooked variation in traits, plant breeders can find nearly endless solutions to the challenge of adapting crops to growing under changing climatic conditions.
