The global seed trade is not as reliable as we thought. Researchers from CABI (Center for Agriculture and Bioscience International), as well as the Swiss research center WSL and other institutions have shown that seeds also contain many pests and fungi, which is a high risk for trees and ecosystems.
Non-native pests and pathogenic fungi represent one of the greatest threats to trees and forest ecosystems worldwide. These exogenous organisms can disrupt forest ecology and cause significant economic losses. For example, the Asian ash borer has extensively destroyed ash stands in North America. Since then, this insect has also attacked ash trees in western Russia and threatens ash trees in Europe. Similarly, in the early 20th century, the fungus Cryphonectria parasitica almost eradicated horse chestnuts from all over North America, which profoundly changed the composition of forests originally rich in horse chestnuts.
Iva Franić, René Eschen and Marc Kenis from CABI, as well as researchers from the WSL Institute and other institutions, analyzed for the first time in recent years the insects and fungi present in seed lots. The study published in the journal Ecological Applications indicates that for some species, the rate of seed contamination has reached an alarming level. They stress that it must be checked whether the protective measures in force for the international seed trade are sufficiently strict.
Using radio and DNA analysis, researchers investigated the presence of insects and fungi on 58 commercial seed samples for 11 softwood and hardwood species in North America, Europe and Asia. Their results converge towards recommendations to reduce the risks of contaminations. The main measure would be to improve the methods of analysis of border health inspectors.
Iva Franić, main editor of the study 'Are traded forest seeds a potential source of non-native pests?' says: "The number of plants imported from China to be grown in Europe has increased sixfold between 2000 and 2018; they now equal imports from North America. "This is a real challenge for the EU's border control agencies.
High rate of insects and fungi
DNA analysis showed that fungi were present in all seed lots. About 30% of the lots contain insect larvae. The researchers also found that the presence and diversity of fungi is much more important than the diversity of insects, especially for hardwoods.
CABI's René Eschen says: "The seed trade of most species is not regulated as seeds are considered less at risk than other plants. The fact remains that the lots contain a lot of mushrooms and insects. "
Simone Prospero of WSL adds: "The high rate of seed contamination is an indication that potentially pathogenic agents can be spread through the seed trade. There is danger in delay".
There is an urgent need for convincing procedures to reduce the lifespan of pathogens in seed lots and to regulate seed trade that is particularly prone to the presence of these agents. In order to improve the risk assessment, detailed information should be available on the species that may be attacked, but also on how the fungi spread on the seedlings and the consequences that follow.