National Post (National Edition)
Sweet potato will likely always be know to the average person as sweet potato. But to scientists?
Scientists unite to solve a potentially costly taxonomic puzzle
Every Friday, the Convolvulaceae Network gathers virtually to discuss all things related to the morning glory family. Taxonomist Ana Rita Simões of Royal Botanic Gardens, Kew in the U.K. and researcher Lauren Eserman of the Atlanta Botanical Gardens in the U.S. started the seminar series in September 2019 as a space for scientists to share their work.
The group grew organically, from the fewer than 50 people who joined the first Skype call — during which Eserman presented her work on the evolution of storage roots in morning glories — to roughly 150 today. Now held via Zoom to handle the crowd, its fluid membership joins the discussions, seminars and collaborative meetings from nearly 20 countries, including Brazil, China and Mozambique.
“It's really diverse,” says Simões. “You get anyone from working in very fundamental science — like really theoretical stuff — to people who work in more applied science. So they work directly with farmers of sweet potato, or work in horticulture. It's been really enriching because everyone brings their bit and then we can help put pieces of the puzzle together. We can help to solve some problems.”
One such problem has to do with saving the sweet potato's identity. Convolvulaceae is a family of roughly 1,880 species and includes the sizable genus Ipomoea, 900-species strong. The family's largest genus, Ipomoea encompasses ornamental and weedy morning glory flowers, and the sweet potato — the seventh most important crop in the world.
Genetic studies, though, have clouded this categorization in showing Ipomoea to be made up of two groups, rather than one. In the spirit of improved classification, this enhanced understanding of plant genetics could potentially result in a future name change for the sweet potato. And in this case, there's much in a name: it could come at a cost to the food industry, conservation and global food security.
On the Friday I joined the Convolvulaceae Network's weekly seminar, Eserman presented a collaborative proposal to preserve the plant's scientific name: Ipomoea batatas. For their new paper published in the journal Taxon, Eserman and Simões brought together a group of 41 sweet potato specialists across 17 nationalities and five continents (including Joanna Rifkin and John Stinchcombe of the University of Toronto's department of ecology and evolutionary biology) to find a fresh solution to an old problem.
The issue stems from when Swedish botanist Carolus Linnaeus first described the genus Ipomoea in 1753, naming not one but 17 species, Simões explains. Every time a new species was described and compared, and found to be similar to any of those 17 species, it could be named Ipomoea. The genus has been expanding ever since.
Advances in DNA-based plant classification have shown that Ipomoea is made up of two distinct groups: sweet potato and morning glories in the first, larger group (roughly 600 species); and plants native to Africa and Southeast Asia, many of which are threatened in the wild, in the second, smaller group (about 300 species).
These two subsets of Ipomoea have been on “basically separate evolutionary trajectories for about 20, 25 million years,” Eserman said in her presentation. “So grouping everything under a single, large Ipomoea, you lose some of this evolutionary information.”
Tiger's footprint (Ipomoea pes-tigridis), a plant in the second, smaller group, has been used to define the genus Ipomoea since the 1970s. Called the type species, it is especially significant because it represents the genus as a whole. When DNA studies revealed the evolutionary gap, the sweet potato and its morning glory relatives in the first, larger group risked being renamed.
“Basically, all those 600, some of them really economically important, (could) be renamed. All for the sake of sticking to a rule, a very strict rule, that could be changed,” says Simões. “Some people who are more conservative would say, `Well, you have to stick to the rules. If someone said in the `70s that this is the type species, then you just really have to rename sweet potato and it doesn't matter.' What we've tried to do is say, actually, no. Let's try to find a compromise here. Maybe we do have to bend the rules a bit.”
In their proposal — which will be voted on at the 2023 International Botanical Congress in Rio de Janeiro, Brazil — the scientists suggest changing the type species for Ipomoea to one closely related to sweet potato.
They've chosen Ipomoea triloba, which is a member of the first, larger group encompassing sweet potato and morning glories, and is one of the 17 species Linnaeus originally included in the genus.
“We want to choose a type species for this group Ipomoea so that whenever someone wants to describe a new species in this group, they know exactly what to compare it with,” says Simões.
With an annual production of roughly 90 million metric tons, a hypothetical name change could be costly to sweet potato breeders, producers and regulators worldwide, Eserman explained in her presentation. Promoting a new scientific name for the sweet potato could lead to communication breakdown between scientists and the agricultural community, not to mention costs passed on to consumers.
From the actual sweet potato roots to products made from them, such as bread, candy, chips, flour, noodles and pectin, all labelling, packaging and documentation would have to be changed. “Anything that you can think of that would involve the name of that species would have to be updated and that's a cost,” says Simões.
If voted in, this bend in the rules would keep the group with the highest diversity intact while preserving the identity of the economically important sweet potato and aiding conservation efforts for the threatened wild species in the smaller, second group, the scientists say, which can be renamed as science progresses.
“It works both ways. Those species to be renamed, it's going to be easier to conserve them. And the other species that are closely related to sweet potato, it's going to be easier to work with them on all these aspects of more applied science towards strategies for food security and fighting effects of climate change,” says Simões, adding that specialists working with the second, smaller group would welcome a change in identity.
“A lot of them are threatened in the wild and they do need conservation action. In Thailand, some of these species are flagships for some protection — they've created parks around these species — so the fact that they're named Ipomoea in those countries is actually negative because they're associated with the crops and the ornamentals … By renaming it something else, it makes it so much easier for our colleagues on the ground to make a case for protecting them because it can be set aside from this other, mostly American, cultivated and more weedy species.”
As a reflection of evolutionary relationships, species names are significant when it comes to future-proofing crops and safeguarding food security. In studying characteristics of the sweet potato, such as disease-resistance, drought tolerance, and starch or water content in roots, researchers would turn to its close relatives to determine if they have similar characteristics and if they would be useful for breeding.
If producers in Uganda, for example, wanted to find an alternative to the sweet potato, which originated in Central and South America, they might try to find other species that are closely related to it. They may turn to the wild relatives of sweet potato, which might be suitable for cultivation and are native to East Africa. But to do that, Simões underscores, you need to know which species are most closely related to sweet potato. And this is especially difficult when you're dealing with a large genus.
“You want as much genetic diversity as possible. You want people to be growing their own food locally and you want to make sure that whatever they're growing locally is nutritious enough to solve possible famine due to climate change,” says Simões. “In this case, it just makes it more effective if we can name the species closely related to sweet potato the same … so that the other species that are not related are not included, or not prioritized in those crop studies.”
Communicating the implications of the group's work, Simões says, is a way of conveying the direct impact taxonomy can have on people's lives. The approach they're taking with the Convolvulaceae Network has already had a ripple effect: another group of scientists used it as a model when starting a similar virtual seminar focused on nightshades, called Solanaceae Seminar Online.
Regardless of the outcome of their proposal, Simões sees it as an example of the power of diversity in collaboration and a way to deconstruct the notion that science is somehow removed from the realities of everyday life. She also hopes it, like the Convolvulaceae Network, will encourage other scientists to work together more often.
“Twenty-first century science should be like this: People from different fields getting together discussing solutions. Technology allows it today so there's really no reason not to do it,” she says. “We also hope that it's inspiring that science can be a bit more open to society and to understand all these challenges we're facing ahead — like food security and climate change. We need to be open to understand that at a societal level and work towards fighting those challenges.”