Wild relatives: The amazing and useful ancestors of our modern crops
Witnesses of selective breeding of crops, wild relatives are also crucial for breeders thanks to their genuine germplasm
Did you know that Oignon comes from eastern India and Sugarcane from New Zealand ?
It all started from a plant that people were harvesting from the wild, and little by little they "domesticated" it into a crop. Pretty much every plant used in food today comes from that process of natural selection over a few thousand years.
But these domesticated varieties were very different from today crops. Usually smaller, less sweet, less productive, more tasty and more resistant to diseases. For instance, modern varieties of Apple contain less than 3% polynutrients than its Nepalese bitter relative Malus Sikkimensis (Sikkim crapapple)¹.
Ancient farmers in what is now Mexico, used to cultivate Teosinte about 10 000 years ago. It seems they already managed to yield about 0.5 tons per hectare, so a group of 25 people needed about 7.5 hectares to live from that crop, Corn's wild ancestor².
Corn is 1000 times bigger than his herb-like relative
Ancient farmers used to keep the seeds of the best harvest for the next year's seedlings, and year after year this method has lead to great improvement of the varieties³.
"In 9000 years, sweetcorn has become 1000 times larger, 3.5 times sweeter, much easier to peel and much easier to grow than its wild ancestor. It no longer resembles the original teosinte plant at all. Around half of this artificial selection happened since the fifteenth century, when European settlers placed new selection pressures on the crop to suit their exotic taste buds." James Kennedy, VCE Chemistry teacher at Haileybury, Australia⁴.
That process lead to the creation of Corn from Teosinte, with a yield three times more important: Around 1930 the average yield of a corn field was about 1,5 tons per hectare⁵.
In addition, during the 20th century, modern breeding techniques and agricultural practices have contributed to an explosion of the yield, nowadays around 10 tons per hectare⁶.
Using these new varieties definitely enables farmers to feed more people with the available arable land, but it may be important to keep an eye on the ancestors of these varieties...
USDA-NASS. 2005. Annual crop production estimate. USDA-NASS, Washington, DC
Interest of crop wild relatives for breeders
It's always amazing to compare modern vatieties to their wild relatives and imagine our ancestors picking up these tiny, sour, sugarfree and pretty dry fruits, cereals or beans.
More seriousely, these wild cousins of our modern crops can be really important for agriculture. Mainly because they represent a vast source of genetic diversity that can be used to improve crops.
According to Maxted and Kell (2009)⁷ who have studied 291 papers about the use of 189 CWR taxa on 29 crops, the key useful traits can be classified as below:
- 39% disease resistance
- 17% pest resistance
- 17% quality
- 13% abiotic stress tolerance
- 10% yield increase
Breeders utilize traits in crop wild relatives (CWR) to improve crops, generally to develop climate-resilient crops. Natural crosses are sometimes possible, or genetic engeneering used to add a specific trait to a modern crop. This process is not trivial, as one breeder tells Guarino and Lobell: ‘it’s a bit like crossing a house cat with a wildcat. You don’t automatically get a big docile pussycat. What you get is a lot of wildness that you probably don’t want lying on your sofa’⁸.
Another example of using crop wild relatives has been revealed by Wageningen University & Research last month: Dr Vosman has is working on a wild tomato species from the Galapagos Islands that is resilient to several pests, and highly resistant to whiteflies.⁹
How to manage line segregation and hybridization processes nowadays
Modern breeders get much help from technology in order to discover new varieties. Biotechnology can be used to transfer a gene from a crop wild relative to a variety, or hybridization and segregation. Then a lot of testing is required to validate the benefits of the new variety.
These operations take several years and involve great amounts of data to collect, store and querry. A database software can be really helpful to manage this data and pilot all the processes involved. RnDExperience™ for instance supports all the actors of a research department to conduct such breeding and testing operations: Collect data, manage germplasm, run biotechnology operations, conduct hybridization and segregation, testing, and analyze data throughout all the project
Dynamic genealogy graph generated with RnDExp™, representing a hybrid’s original parents and other hybrids sharing at least one original parent.
"In this example a user can select a hybrid in the grid and evaluate hybrids sharing an origin parents with it, [...] the shared parent can be selected and its untested descendants included in next year’s trials."¹º
In fact the generation C016HY0104 (bottom line green) results from the hybridization between PINTO (pink & green family), ZOBRA (blue and green family) and ASTON (bottom line). This dynamic graph enables to study all its relatives and their performances (yield, quality).
Breeding the Nutrition Out of Our Food by Jo Robinson on the New York Times
Map of the distribution of wild Tomato species by the Tomato Genetics Resource Center
Land of the wild tomatoes, by Sandy Knapp, Museum botanist on field work in Peru, on the website of the British National History Museum
¹ Eating on the Wild Side: The Missing Link to Optimum Health, Jo Robinson (Read an extract online on Google Books)
⁵ Teosinte as a Grain Crop, John Doebley, Laboratory of Genetics, University of Wisconsin-Madison, https://teosinte.wisc.edu/grain_Crop.html
⁶ USDA-NASS. 2005. Annual crop production estimate. USDA-NASS, Washington, DC
⁷ Maxted, N. and Kell, S.P., (2009). Establishment of a Global Network for the In Situ Conservation of Crop Wild Relatives: Status and Needs. FAO Commission on Genetic Resources for Food and Agriculture, Rome, Italy. 266 pp
⁸ 2011 Guarino, L., and D.B. Lobell. 2011. A walk on the wild side. Nature Climate Change 1, no. 8: 374–5. doi: 10.1038/nclimate1272
⁹ Close relative of the cultivated tomato is resistant to many insects: https://www.wur.nl/en/newsarticle/Close-relative-of-the-cultivated-tomato-is-resistant-to-many-insects.htm
¹º 2017 Zinn & al. How interactive genealogy graphs enable to explore a hybrid's extended family and study the performances of its members for mutliple traits, all within RnDExp, PAG 2017. https://www.doriane.com/medias/fundamental/2016-12-23-pag-final.pdf