What is a market? What feelings does it stimulate? What is your definition about it? The Oxford dictionary defines it as «A regular gathering of people for the purchase and sale of provisions, livestock, and other commodities». However, I think a market is more than that. Much more indeed. A market is something much more romantic, more poetic if I may say: a market is a window to the World. Let me explain it using the picture above as an example, taken in a market somewhere. Colourful shelves, products from every corner of the Planet: tomatoes, bananas, oranges, potatoes, peppers. We can travel all around the world with a quick glance to the labels. How many of these products, which we can now consume all year round, were sold in Europe centuries ago? Almost none; possibly this is the clearest example of globalisation. Now, come with me one step further.
Labels indicate the place of cultivation of the plants we eat; however, an in-depth study reveals an even bigger revolution: the true globalisation. Most fruits and vegetables that we eat are cultivated thousands of kilometres from us, but also a long distance from the places where they originated. In fact, most cultivated plants have their main producer far from their place of origin. As an example, China is now the biggest producer of tomatoes worldwide and most tomatoes eaten in Europe come from the Netherlands, but they originated in Mesoamerica. That is, the plant is native to the American continent, but nowadays its main producer is more than 10,000 kilometres away, across the Pacific Ocean. Other examples that call our attention are the apples, starring product of the British Islands but originated in the Caucasian region; or the potatoes, tubers of Andean origin so important for European diets that their lack caused the Great Irish Famine and, ironically, obliged millions to emigrate to America. This pattern occurs in many other plants, from oranges and bananas and many others.
So, where does our food come from? And above all, why is it important to know its origin?
Perhaps surprisingly, it is extraordinarily important to know where cultivated plants originated. To identify these places is essential to find the wild form from which the cultivated species originated (if that wild form still exists) and its wild relatives: other species evolutionarily very closely related to the plant cultivated by humans. Now, you may wonder: why is this relevant?
Much like animals, plants can be domesticated too. For generations, sometimes during thousands of years, we humans have selected varieties with traits that made them more desirable: larger fruits, faster growth, seeds that take longer to fall —something really useful to harvest cereals—, et cetera. However, this artificial selection has had collateral effects: through favouring specific varieties with traits interesting to humans, cultivated species have lost part (sometimes great part) of their genetic diversity. This genetic diversity facilitates plant adaptation to changes in the environment like prolonged drought, higher temperatures or raise of new pathogens, and thus in principle cultivated plants could have poorer responses to unexpected changes in the environment that their wild relatives[1, 2].
In a scenario of climate change and intense human pressure, loss of genetic diversity is the main threat to food security. Not in vain, some plants are already affected by their low genetic diversity: bananas and apples, for instance, are in danger of collapse.
Luckily for plants and for ourselves, not everything is lost. We count on the wild relatives of the cultivated plants. These wild plants are genetically very similar to cultivated plants and maintain their genetic diversity almost intact, because they have not gone through the artificial selection that affected crops. Therefore, wild relatives constitute a very interest potential source of genetic diversity to improve their cultivated relatives.
Unfortunately, and surprisingly as it may be, we do not know the origin of many plants cultivated by humans, or we only have an incomplete knowledge. This was the case, until very recently, of the sweet potato (Ipomoea batatas (L.) Lam.), one of the most widely consumed plants in the world and a staple in many countries, especially in developing one. In addition, for its content in beta carotene, the sweet potato is a main food to help address vitamin A deficiencies, which affect millions of children worldwide. Despite its importance, decades of studies have been necessary to identify the wild species from with the sweet potato originated: in other words. We, a group of researchers from the United Kingdom, Peru and the United States, have devoted the last four years to resolve this enigma. In order to do we had to identify, in the first place, the group of plants to which the sweet potato belongs, its wild relatives: fifteen species distributed across the American continent and from South East Asia to Madagascar, extraordinarily variable in their morphology and with overlapping distribution areas. Next, we needed enough material to represent the diversity existing within the group, which we obtained collecting samples from the field, from herbarium specimens and from seed banks; since the sweet potato is original from the American continent, we looked for specimens mainly from this continent, but also from Africa and Asia, were sweet potatoes have been cultivated for centuries. Finally, we had to thoroughly study the DNA of all these samples to understand the evolutionary relationship between them. The main result was to reveal that the species from which the sweet potato originated is Ipomoea trifida Kunth (G.Don), a species distributed from southern Mexico to northern South America. On one hand, this discovery indicates that, most likely, the sweet potato originated in that part of the American continent. On the other hand, our research opens the door to utilising the wild relatives in breeding programmes to incorporate new genetic diversity into the cultivated plant and, ultimately, to improve the quality of a crop that is extraordinarily important in developing countries.
In summary, to understand the origin and evolution of the plants that we cultivate is essential, not only to improve the biological knowledge of these species, but it is the first step to develop research strategies that allow to improve the quality of the plants that we use, many of the essential for the development of human societies.
By Pablo Muñoz Rodríguez. D.Phil. Student, Department of Plant Sciences, University of Oxford. Oxford SRUK Constituency.
1. Abbo, S. et al. (2003). Evolution of cultivated chickpea: four bottlenecks limit diversity and constrain adaptation. Functional Plant Biology, 30(10): 1081-1087.
2. Berger, J.D. et al. (2011) Domestication bottlenecks limit genetic diversity and constrain adaptation in narrow-leafed lupin (Lupinus angustifolius L.). Theoretical and Applied Genetics, 124(4): 637-652.
3. FAO (2010). Crop biodiversity: use it or lose it. Disponible en: http://www.fao.org/news/story/en/item/46803
4. Muñoz-Rodríguez, P. et al. (2018). Reconciling conflicting phylogenies in the origin of sweet potato and dispersal to Polynesia. Current Biology 28. Available at: https://doi.org/10.1016/j.cub.2018.03.020
5. Austin, F. (1978). The Ipomoea batatas complex – I. Taxonomy. Bulletin of the Torrey Botanical Club, 105(2): 114-129.
6. Khoury, C. et al. (2015). Distributions, ex situ conservation priorities, and genetic resource potential of crop wild relatives of sweetpotato [Ipomoea batatas (L.) Lam., series Batatas]. Frontiers in Plant Science, 6: 251.