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Seeds and the introduction of harmful organisms

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Tree seedlings and seeds are today traded widely across Europe and the world. Seed is imported not only when it is cheaper to buy abroad, but also as part of a lively trade in the seeds of exotic ornamental plants to liven up parks and green areas. Whether the seed and plant material are free from harmful organisms, such as insects and fungi, is a question that arises at the latest at the Swiss border. Alien organisms may be introduced into a country with the imported seeds. The organisms could then, depending on the circum­stances, reproduce and spread uncontrollably in their new environment.

When importing wood and living plants, official documents are required that confirm the plant material is healthy. But no such documents are necessary for importing seed because it is considered less dangerous. The seed trade is therefore not regulated for most tree species.


Carry out test planting prior to export

But the risk could be greater than previously thought. The biologist Iva Frani´c checked seeds from North America, Europe and Asia for insects and fungi for her doctoral thesis at WSL and the Centre for Agriculture and Bioscience International (CABI) in Delémont. It turned out that the seed samples of some tree species from China and North America are far more infected with fungi than previously assumed. The fungi included species that are already known as pathogens. Simone Prospero, who is supervising Iva’s doc­toral thesis at WSL, says: “The high infection rate of some tree species’ seeds is worrying.”

It is not yet clear whether all insect and fungal species found are dangerous and how great their damage potential is. To find out, researchers from WSL and CABI Delémont will perform infection tests with plant material and genetic analyses at WSL’s Plant Protection Lab in Birmensdorf.

Another method for identifying potential pests is so-called ‘sentinel planting’, which is already carried out in the seeds’ country of origin. This involves planting the seeds of frequently exported tree species and then examining the plants for harmful organisms. The final decision about exporting the seed and plant material is based on a risk analysis to assess whether these organisms could become invasive in one of the importing countries. One such plantation was established in WSL’s experimental tree nursery in Birmensdorf in 2018. Here, five tree species native to Central Europe that are regularly exported to Asia are being checked for fungi and insects.


Seed testing required

From the results so far, the researchers conclude that it is essential to reconsider phytosanitary measures in trading tree seed. “The risk of un­intentionally introducing harmful organisms can only be minimised if seed samples are tested for fungal and insect infestation in their country of origin, and each sample then receives a corresponding certificate,” explains Simone. The earlier and more accur­ately invasive pests are identified, the easier it is to prevent their introduction into countries that were pre­viously free of infestations. “The new plant health regulations of the EU and Switzerland are a step in the right direction,” Simone maintains. These regulate the import requirements for plant material from third countries such as China more strictly. Once pests have spread across continents, the financial and ecological consequences can be immense.

(Lisa Bose, Diagonal 2/19)

The WSL plant protection lab »