The CGN safeguards the diversity of our lettuce, pigs, apple trees – and now also eel

In early 2025, Nature published a massive analysis of Earth's genetic diversity, the most comprehensive yet. The authors used data from more than three decades, on 628 species of animals, plants and fungi. What transpired? In two-thirds of these species, genetic diversity is declining - and that is a problem. Homogenous species, for example, may be more susceptible to disease or have greater difficulty adapting to a changing environment over the long term. 

Genetic diversity is also important for humans, for example when it comes to food such as vegetables, fruit, milk, eggs and also natural products, such as wood. “The crops that are eaten around the world were created by agriculturalists who crossed all kinds of species,” explains Theo van Hintum. “For example, they create varieties that are more drought-resistant or disease-resistant.” Van Hintum is the head of the plant programme at the Centre for Genetic Resources, the Netherlands (CGN), part of Wageningen University & Research (WUR). The CGN preserves crops, shrubs, trees and farm animals.

According to the meta-analysis in Nature, human activities are a major cause of the disappearance of diversity in nature. The CGN's activities are a crucial counterbalance. The Netherlands and WUR are therefore investing in an even more robust gene bank - with a larger collection and better facilities - which is ready for the future.

Gene banks emerged in the 1970s, when genetic diversity was in danger of disappearing for a very different reason. “Developing countries then started replacing their local grains and vegetables on a large scale with newly improved varieties that had higher yields, for example,” says Van Hintum. However, the local breeds that were in danger of disappearing in the process represented a treasure trove of genetic diversity. “To conserve the genetic material of those old varieties, the first gene banks were created.”

“Thank goodness. Otherwise, our world might look very different now,” says Van Hintum. “That may sound exaggerated, but the spinach that is on our plates now has been improved using material we once collected in Central Asia.” In total, the centre's freezers contain more than 24,000 seed samples, as well as more than 300,000 doses of semen from cows, pigs, horses and other farm animals. The field collection of the trees and shrubs department consists of more than 4,500 specimens.

“That does not make the CGN a very large gene bank,” Van Hintum says. “Not so long ago, we were ranked 15th in Europe.” Despite the Netherlands being one of the world's largest exporters of plant seeds and other propagating material. “98.8% of our collection is readily available for distribution to agriculturalists, breeders and researchers.” The gene bank felt it was time to grow and the Dutch government agreed. By 2032, the CGN wants to have doubled its collection compared to 2022 and to have moved into a new, central building.

The crop collection includes samples of more than 30 different crops, such as carrots, maize and potatoes. These can be all kinds of varieties: from varieties that until recently were still cultivated in the fields to so-called 'heritage varieties' that are also preserved for their cultural-historical value. With 2,500 different lettuce samples, the CGN has the best lettuce collection in the world, according to Van Hintum.

Rik Lievers leads the crop department expansion programme. The focus here is on both the usefulness for the agricultural sector and the socio-cultural value of varieties. The genus Phaseolus, which includes string beans, green beans and brown beans, is one of the species selected for expansion. Although the bean is originally from Central America, the Netherlands does have a history with the crop - particularly the brown bean. Lievers: “The crop is now mainly found in vegetable gardens, but pulses may increasingly be grown on a commercial scale as an alternative source of protein.”

“We are expanding in three ways,” says Lievers. “Namely by taking over collections from other, less well functioning gene banks, by setting up collection missions, and by selectively storing modern varieties.” The new Phaseolus collection will partly consist of material now held by other gene banks. “Some gene banks do not have the facilities themselves to properly store or propagate the material. The CGN does. That way, these varieties will again become accessible for breeding and research worldwide.”

New wild varieties are tracked down during collecting missions. For example, the CGN collaborated on a mission in Albania, adding wild parsnips and carrots to the collection. “Our foreign colleagues get involved in such a collection mission. The CGN assists them with knowledge on quality preservation and other aspects of the conservation process.” New varieties need not be tracked down; they are produced in the Netherlands. “Take lettuce. Hundreds of new varieties are bred every year, so experts select for us the varieties that really add something to the collection.”

Seeds of lettuce, carrots, maize and other agricultural crops are frozen, according to carefully developed protocols. However, the collection also includes native trees and shrubs: wild apple, cherry and lime, for example. Until recently, these were only preserved in a 'living gene bank', planted fields managed in collaboration with the Forestry Commission. That form of conservation has drawbacks, says biologist Seppe De Mits. “The diseases that threaten biodiversity in the wild, such as ash dieback, also threaten our living gene bank collections. Or consider the changing climate, which could also be a problem for these species.”

De Mits and his colleagues are therefore working on ways to also freeze the seeds of trees and shrubs. This is not always easy. “The tree seeds we collect in the Netherlands fall into two categories: orthodox and recalcitrant species,” explains De Mits. “Orthodox seeds are easy to dry and freeze. With recalcitrant seeds, as the term suggests, this is more difficult. Recalcitrant seeds are not good at withstanding the drying process. If you freeze those kinds of seeds at the usual -20° Celsius, ice crystals form internally and damage the material.” 

“At the moment, we are experimenting with liquid nitrogen. Liquid nitrogen is minus 196°, which allows seeds to be frozen extremely quickly. At that speed, crystal formation could be prevented.” For those experiments, De Mits and his colleagues are assisted by the farm animals team, who have been working with cryo-storage for much longer. De Mits notes that such collaborations will become even more natural when all CGN employees are finally working together under one roof, in the new building.

In 2003, the CGN took over the tasks of the Genenbank Landbouwhuisdieren Foundation, which had been collecting genetic material from farm animals since 1960. The CGN steadily expanded this collection to include both rare Dutch varieties and more common varieties that play a role in food production worldwide. In 2024, sperm of the black bee, which is only found in the Netherlands on Texel, was frozen. Bees suffer greatly from biodiversity loss and climate change, but even common farm animals can rapidly lose genetic diversity, due to outbreaks of foot-and-mouth disease or avian influenza, for example.

The CGN monitors the status and trends of over 140 Dutch farm animal breeds and advises breed societies on how best to maintain genetic diversity within the population. That includes aquatic species, such as mussels, seaweed - and now eels. The Dutch aquaculture industry often still uses source material from wild populations for rearing. The CGN therefore works with Wageningen Marine Research to monitor these too, and also includes genetic material from these species in its collection. 

Storing eel semen proved challenging. “The quality starts to drop as soon as the material leaves the animal,” says Annemieke Rattink, the head of the CGN animal programme. Experiments with different freezing protocols did not immediately give the desired results, despite the high quality of the semen. “So we contacted the experts at Valencia Polytechnic University. Even with their freezing protocol, we still did not manage to freeze the sperm immediately - we had to fine-tune it ourselves.”

Then it worked: the frozen and thawed sperm retained an average of 40% motility. In fact, it has already managed to use that sperm to fertilise fresh eggs and produce elvers. “Scientists just haven’t yet managed to grow those eel larvae into adult eels in the lab - and neither have we.” And that is not the only challenge facing Rattink and her colleagues. “We are now also trying to freeze the eggs of eels. That is even harder, because they are much bigger than sperm cells.”