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GENETIC SOURCES

A living collection of rare trees

A living gene bank with indigenous trees and bushes in the Roggebotzand woods in Flevoland. Photography: Wageningen University & Research

KENNISONLINE 2020


It is crucially important for woodlands to retain sufficient genetic variation if they are to adapt to new diseases and climate change. That is why Wageningen University & Research is helping set up a living collection of rare indigenous species of tree.

The Netherlands has more than a hundred species of indigenous trees and bushes. Many are severely endangered as humans have been manipulating the landscape for centuries and the Netherlands’ original vegetation from prehistoric times has largely disappeared. At most five per cent remains.

Take the example of the wild apple. There are perhaps at most 250 wild apple trees growing dotted around the Netherlands and Flanders. Wild apple trees like light, open places but Dutch woodland is becoming ever denser and darker due to changing forest management practices. The wild rose is another plant in trouble.

Genetic diversity

As a signatory of the Convention on Biological Diversity (CBD), the Netherlands is obliged to maintain levels of biodiversity and take appropriate measures to preserve the genetic sources of indigenous trees and bushes. Wageningen University & Research (WUR) is ensuring that the genetic diversity of trees and bushes is maintained.

The Flevopolder houses a living gene bank with wild examples of indigenous trees and shrubs, such as the wild apple. WUR researcher Joukje Buiteveld explains why the gene bank is important and how it contributes to long-term sustainable forest and nature management.

“We are not only working hard to conserve indigenous trees and bushes, we are also encouraging their use, for example by planting them again in nature areas,” says Joukje Buiteveld of WUR’s Centre for Genetic Resources, the Netherlands (CGN). “Genetic diversity among indigenous trees and bushes is important as it is the basis for sustainable forestry and nature conservation in the longer term. For example, woodlands need to be able to adapt to climate change and new diseases and pests.”

Sustainable basis

The classic gene bank as used for agricultural crops is not a good solution for trees and bushes as most tree seeds do not survive long in a freezer. They cannot cope with dehydration and they rapidly lose their ability to germinate. That is why various indigenous trees and bushes have been planted since 2002 in the Roggebotzand woods, run by the nature management agency Staatsbosbeheer in Dronten in Flevoland province. “It’s a living collection,” says Buiteveld.

The gene bank safeguards the genetic sources of our indigenous trees and bushes

Buiteveld and her colleague Paul Copini provide the scientific support for the gene bank in Roggebotzand and they are responsible for documenting the collection. Staatsbosbeheer is in charge of the practicalities, such as planting the trees and harvesting seeds. There are now around 4800 genotypes of more than 50 indigenous species on 28 hectares, and that number is increasing. CGN advises Staatsbosbeheer what genetic material the gene bank should contain in order to reflect the Netherlands’ overall genetic diversity.

Fragmented

The gene bank also functions as a ‘seed garden’ from which Staatsbosbeheer harvests seeds to provide seedlings for use in nature areas. Buiteveld: “Human activities have led to the fragmentation of populations of indigenous plants and it is very difficult for ‘singletons’ to find one another. That makes the natural exchange of genetic material a lot trickier. Bringing the plants together in the gene bank enables natural pollination, resulting in better flowering and improved development of fruits and seeds.” This not only lets the gene bank preserve the genetic sources of trees and bushes for the longer term but also facilitates the production of seeds and shrubberies with maximum genetic diversity.

The European white elm is included in the living tree collection in Roggebotzand. Photo: Leo Goudzwaard

Buiteveld: “The Roggebotzand collection contains 140 wild apple trees, for example. Each tree is genetically identical to the original wild tree from which the cutting was taken. In the collection, the apple trees stand next to one another, which lets them pollinate one another and produce seeds.” Soon it will be possible to take the seeds from the little sour, tart apples now growing on the trees. The seedlings will be planted in nature in order to reinforce the remaining small populations growing in the wild.

Buiteveld and her colleagues at Wageningen Plant Research are also using molecular markers to test the apple tree collection for genetic affinities and purity. Hybrids with commercial apple cultivars are removed, as are ‘duplicates’. Some of the material that was added to the gene bank 15 years ago has now died out completely in the wild.

Essential

Buiteveld: “The vulnerability of a living collection is still a cause for concern. We are looking at the options for making backups. Perhaps we could freeze the seeds of some species after all, or plant a second living collection in a different location. The Flevopolder does not provide the optimum environmental conditions for every species of tree or bush anyway. Obviously the best solution is if you can safeguard the gene sources by better protecting the original habitat. But most species in our collection are already so rare that inclusion in our gene bank is simply essential.”

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