Walk through the New York Botanical Garden in the Bronx (NYBG), past the exotic orchids, blossoming bougainvillea, swaying grasses, and a patch of pristine forest like the one that was here when the Dutch arrived in the 17th century, and you’ll likely miss the most significant plants in the place. Scattered amidst the displays of boisterous and fragrant vegetation, in one of the most celebrated plant collections in North America, are the wild relatives of our most important food crops.
In their untamed form, they’re barely recognizable as in the same family as the fruits and vegetables on our dinner plates. But there they are—the crenellated leaves with little yellow flowers in the genus of Brassica, progenitor of broccoli, bok choy, Brussels sprouts, turnips, and cabbage; the fernlike leaves of the Juglans genus of walnuts, pecans, and hickory nuts; and even a couple of short, wild banana trees.
They may not look familiar, but scientists are discovering that many of them have characteristics that are critical to the survival of crops facing the tumultuous shifts in growing conditions triggered by climate change. Only a fraction of the wild relatives of food crops have been collected in any systematic way, but the hunt is on for them as plant scientists come to understand the important reservoirs of genes they possess from the mere fact of having survived so many seasons of changing conditions.
“Climate change drives home the importance of preserving wild landscapes, because they harbor plants important to our food security.”
Many of us humans have cousins or aunts or uncles who may not conform with the rest of the family, who embarked on a different path, and yet are part of our family’s fabric—our “wild relatives.” The same thing exists in the world of plants. From the grasslands of the Midwest to the Eastern seaboard, from the mountains of Central Asia and Mexico to the dry gulches of Arizona come the undomesticated family members of the plants we have tamed as food.
But they remain wild, out there growing on their own, evolved to ecosystems that may be far away from the fields where their domesticated cousins are cultivated to feed us. They haven’t been propped up with pesticides or weaned on fertilizers. They have adapted.
In many Indigenous communities, farmers encourage their growth along the borders of their farms to foster cross-fertilization between their crops and these hardy varieties. But most industrial agriculture treats them as more like unwanted weeds. That is a mistake, says Alex McAlvay, who runs the NYBG’s crop wild relatives program.
“With the industrialization and homogenization of the food system we have lost many of the characteristics that come from crop diversity,” he said. “Climate change drives home the importance of preserving wild landscapes, because they harbor plants important to our food security.”
McAlvay led a research team last year that identified the Hindu Kush mountain range, stretching across Pakistan, Afghanistan, and Tajikistan, as the source pool of diversity for the Brassica rapa crops, those relatives of Napa cabbage, turnips, and bok choy now growing in the New York garden. The research, published in the peer-reviewed journal Molecular Biology and Evolution, concluded that conserving those varieties was critical “to cope with changing environmental conditions” in the future.
“The real advantage of these relatives is to help with the extreme events that are being aggravated by climate change,” he said. “Resisting drought, flooding, extreme weather events, these are traits that wild relatives tend to shine in and have leveraged to maximum effect.”
A couple of examples: a cousin of wheat, called Aegilops tauschii, growing wild from Syria and the Middle East to the Caucusus—the so-called Fertile Crescent—have bolstered resistance to a fruit fly that’s followed the warming temperatures into the wheat fields of the American Midwest. And the progenitor cousin of corn, teosinte, growing wild in the mountains north of Oaxaca, Mexico, has repeatedly contributed to the breeding of commercial corn varieties resistant to the corn borer and other pests.
A study in Crop Science lists multiple commercialized crops that have benefited over the years from breeding with their wild relatives, including barley, bananas, chickpeas, corn, hops, and wheat.
But three-quarters of the crop seed varieties on Earth in 1900 were extinct by 2015, and the U.N.’s Food and Agriculture Organization predicts we are on the verge of losing as much as a third of the 400,000 remaining varieties. In North America, a recent study in PNAS identified at least half of the “wild relative” populations in North America as threatened with extinction driven by climatic changes and other pressures.
That includes relatives of the apple, plum, blueberry, pecan, walnut, potatoes, wheat, corn, and numerous beans, many of which contain characteristics that could prove critical to the survival of crops facing their own tumultuous shifts in growing conditions. Such stats have triggered alarm in the cloistered world of botanic gardens, institutions known mostly for their blissful detachment from the outside world.
“There are winners and losers in the process of domestication,” said Colin Khoury, senior director of science and conservation at the San Diego Botanic Garden and lead author of the PNAS paper. “Many of those ‘losers’ contain the key to resistance to climate threats.”
After a century of rapid-fire plant extinctions, and on the verge of losing more, Khoury and McAlvay are among a new generation of plant scientists focused on expanding the role of botanic gardens into conserving the relatives of common food crops, which they see as critical to a stable food supply as climate change wreaks havoc with agriculture. The effort involves an unprecedented level of cooperation between gardens and a novel approach to conservation—a dating service for crop wild relatives to ensure their genetic diversity.
A Global Alliance of Gardens
Plants experience climate change as a rewiring of ecological cues. When the temperature rises and the winter comes even a week or two later, as is the case in many parts of the Midwest, bugs have longer to feast on crops. When it doesn’t get cold enough in winter, as has been the case recently in California’s Central Valley, tree-fruits don’t fully develop. After freak torrents of rain during warm weather, fungi have a field day in moist, warm fields.
In evolutionary terms, these volatile shifts are happening at a rapid and accelerating pace. The botanic gardens are starting to look for and identify the ways in which wild relatives survive such climatic changes and what that portends for breeding with their commercialized, edible cousins. The process of domestication often excludes such “survival” characteristics in favor of taste, shape, or other traits perceived as central to the commercial success of foods. Many relatives of cultivated plants were displaced by the monocrop seeds that dominate North America and much of the world. And those cultivated crops are now incapable of adapting to changing ecosystems and are dependent on chemical fertilizers and pesticides to thrive.
But those wild relatives that did survive, did so without human assistance. They adapted, one of the most critical characteristics in this time of high volatility. And because they’re related, they don’t require genetic engineering to pass on traits; they can reproduce them naturally. Growers of wine grapes in California have relied for years on cross-breeding with wild relatives of the grape to provide resistance against phylloxera pests that feed on the roots and leaves of grapevines, which are more vulnerable when weakened, scientists have found, by drought conditions.
Botanists can “read” the seeds and stalks of wild relatives, and, like the stories embedded in the rings of a tree, discern the conditions when they took root, and the stress factors they faced as they grew. Chris Pires, former chief science officer for the New York Botanical Garden, described their herbarium as “like a time machine,” offering insights into past climatic and other challenges that plants are capable of surviving.
Since November, some two dozen botanic gardens in North America have started sharing the details of their holdings for the first time, an effort to inventory how much backup exists for threatened populations of crop wild relatives. Over the past nine months, Khoury and his colleague Abby Meyer, executive director for North America of Botanic Gardens Conservation International (BGCI), convened a series of Zoom meetings between two groups specializing in the wild relatives of tree-fruit and nut crops.
One after another, officials from gardens in St. Louis, Atlanta, San Diego, Minneapolis, Berkeley, Toronto, Vancouver, and elsewhere shared what they have in their collection, and what they perceive to be missing. It was a blur of Latinate names, which took a quick visit to Google to translate—the Prunus (the family of cherry and almond—yes, they’re related), the Diospyros (family to the persimmon), the Malus (apple family), Corylus (hazelnut family), the Juglans (walnut family), and many more.
Each participating garden in the network, including the New York garden, is asked to contribute the characteristics of the wild relatives in their collection to a collective database, the first step in determining which populations are the most inbred and in need of genetic outbreeding. With that metadata, Meyer explained, they are laying the ground for gardens to exchange grafts and seeds in a continent-wide effort to ensure the most genetically diverse, and thus resilient, populations of wild relatives of food crops.
The BGCI was founded by London’s Kew Gardens in 1987 to coordinate global plant conservation. Since then, climate change has raised the stakes, Meyer says.
“We come from the place of trying to demonstrate to our public that climate change is a real thing,” she says. “Recently, our conversations have shifted to, ‘OK, this is the future climate we’re going to be in. It’s going to get hotter, drier, here. It might get wetter and more extreme somewhere else.’ Gardens are saying, ‘This is our future,’ and asking, ‘How do we exist in our future?’”