The deep roots of the vegetable that “invaded the world”


Stray dogs, “wacky” genes and a deep affection which inspires “blasphemous” poetry. The plant known as Brassica rapa has quite a story, a story that, after decades of debate, is finally emerging. The unique species, which humans turned into turnips, bok choy, broccoli rabe (also known as rapini) and other residents of the produce aisle, began as much as 6,000 years ago in Central Asia, most probably in the shadow of the Western Himalayas’ peaks piercing the sky.

Earlier this month, Molecular biology and evolution published results of an unprecedented study on B. rapa which brought together genetic sequencing, environmental modeling and the largest number of wild, wild and cultivated samples ever collected. The team’s results aren’t limited to knowing the genealogy of your next jump: the article is an important step forward in understanding how one of the most important agricultural species on the planet could. resist climate change.

“This study is really great. I love the approaches they took and the framework they put them in, ”says Nora Mitchell, a plant evolutionary biologist at the University of Wisconsin-Eau Claire. Mitchell, who was not involved in the research, is studying hybridization and adaptive evolution. She says that the environmental modeling of the new document – reconstruct the conditions under which B. rapa has been adapted to different locations, as well as predicting what the changing conditions might mean for its future, makes the study particularly compelling. “The multi-pronged approach to understanding the genetics of these different groups, wild sampling and environmental modeling makes the study really robust,” she says.

The work is a special achievement when you consider both the diversity and the global spread of B. rapa the crops, related wild species and wild varieties that escaped farmers’ fields, “taking over the world,” says Alex McAlvay, lead author of the study and botanist at the New York Botanical Garden. Now, he said, B. rapa, in various forms, “grows from Alaska to Tierra del Fuego.” They grow in Oceania, they grow from Spain to Japan.

Domestiqué au Japon, le mizuna est de la même espèce que les navets, le bok choy et de nombreux autres <em>B. rapa cultures</em>.
Domesticated in Japan, mizuna is the same species as turnip, bok choy and many others. B. rapa harvests. Toshimasa Ishibashi, CC BY 2.0 / flickr

“You can go to San Diego, on the coast, and see wild landscapes Brassica rapa, “he adds.” But they’re not really wild. They’re like the stray dogs that escaped and formed their own pack in the woods. B. rapaThe ability to survive as a wild plant all over the world had created a lot of uncertainties as to its origins. Botanists often look to wild relatives of crops to understand where plants were first domesticated. But B. rapa is everywhere and, before new research, distinguishing truly wild species from wild escapees was nearly impossible.

“People had put forward Europe, East Asia, Central Asia, multiple origins,” says McAlvay. Some previous research, based in part on literary evidence, has put B. rapadate of domestication around 2000 years ago, probably in Europe. “We have this prejudice of thinking that everything the Greeks and Romans wrote meant they did it first, and at that point, and I’m very tired of seeing that argument,” he says. . A broader examination of ancient texts from India and China has revealed mentions of B. rapa cultures dating back nearly 3,000 years, McAlvay says, and his team’s genetic analysis of hundreds of samples pushed the start of domestication even further back, to somewhere between 4,000 and 6,000 years ago.

While genetic sleuth work is always a complex undertaking, McAlvay says he and his colleagues have been particularly challenged by a “crazy jumble” of genes from the ancestor of the two. B. rapa and his close relative B. oleracea, another unique species that provides multiple vegetables: broccoli, cauliflower, cabbage, kale, and more.

“One of the reasons we think these species have this incredible diversity is that their ancestor not only had a duplication of their genome, but a triplication,” says botanist Makenzie Mabry, who co-authored the new article at the time. that she was at the University of Missouri. While humans and many other organisms inherit a single set of chromosomes, half of each parent, some plants inherit double sets. the Brassica The ancestor had three sets which, Mabry says, left his descendants “all this genomic space to do really cool and wacky things with.” Lots of genes mean a lot of raw material for adaptability. Even in the extremely diverse plant world, adds Mabry, “people recognize Brassica as being a little “extra”.

La domestication de <em>Brassica rapa</em> savage probably first occurred in the Hindu Kush of Central Asia.
Domestication of the wild Brassica rapa probably first occurred in the Hindu Kush of Central Asia. Objectifnmatter, CC BY 2.0 / FLICKR

Humans have taken this potential for diversity and used it, say botanists, who are also collaborating on future research on B. oleraceathe history of domestication. The story likely began in a narrow, mountainous expanse of the Hindu Kush, encompassing parts of Pakistan, Afghanistan and India, where the first crop to be domesticated was turnip, says McAlvay, “which s ‘is then propagated to the east and the west “.

“There’s an extra layer of strangeness,” on the road to domestication and diversification, adds McAlvay: Different crops selected for certain traits in different parts of the plant. For example, we know tomatoes of all colors, sizes and flavors, but they are all the fruit of the plant. Solanum lycopersicum. For B. rapa, however, “with the turnip you look at the root, the underground stem of the plant. Tatsoi is the leaves. The broccoli rabe is the flower, ”says McAlvay.

“In China, people saw the same type of raw material, turnip, and they did something totally different from what the Italians and the Spaniards did,” he adds, browsing a list of water-rich bok choy, large turnips, bitter greens, shredded leaf mizuna and more B. rapa permutations in the world.

La recherche génétique indique que le navet était probablement la première culture de <em>Brassica rapa</em>, originally from Central Asia up to 6000 years ago.
Genetic research indicates turnip was probably the first Brassica rapa culture, originating up to 6,000 years ago in Central Asia. Franco Folini, CC BY-SA 2.0 / flickr

“These cultures have a lot to say about humans and about human history along the way. These things are found all over the world and, more than most cultures, people grow them in their gardens and have a close relationship with them, ”says Mabry. This closeness has often created a special affection for the plant.

McAlvay shares a Galician saying he translated, from the region of northwestern Spain that is home to three loved ones B. rapa crops: turnips, grelos and nabizas. “Turnips, turnip greens and turnip blossoms, the holy trinity of the Galicians. They are three separate people but one true God,” says McAlvay. “Surprisingly blasphemous from such a Catholic neighborhood (where the Camino ends) de Santiago), but that only shows you how much they love their Brassica harvests. “

Dig up B. rapa‘s roots is more than an exercise in botanical history. Mitchell, who focuses on the wild relatives of farmers’ favorite sunflowers – “one of the few crops that was originally domesticated in North America,” she notes – says people often ask her why it is important to know the origin history of a plant. “Food security is a big problem, especially global food security. And with Brassica having so many crops, not only for vegetables but also for oils, it is really important to keep producing these crop species in the face of climate change, increasing drought and changing nutrients, as well as crop burns and diseases, ”says Mitchell. “It is important to understand not only what happened in the past, but also how these plants might react in the future, and to know what kind of genetic resources could increase diversity.

McAlvay thinks findings from wild and wild strain paper might be particularly important for better breeding B. rapa crops in the future. “For most of recent history, people have rejected the stray dogs of the plant world as not being particularly useful,” he says. “But because they’re already adapted to really tough and harsh environments, there’s a certain pressure, with the advent of gene editing, to take inspiration from these turnips gone wild.”

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