Ash Dieback is a disease which is caused by the invasive fungus Hymenoscyphus fraxineus. It is very likely that the fungus reached Europe through the international plant trade, since studies have shown that it lives peacefully on Asian ash species without harming them. Usually, the fungus is invisible to the eye, but during the winter it forms white fruiting bodies on dead branches on the forest floor.
Today, there is no known cure or protection against Ash Dieback, but if one would try to protect a single ash, one can remove dead branches below it to keep the fungus from hibernating there.
Below, common symptoms of Ash Dieback are shown. The infection usually starts by spores from H. fraxineus entering the leaves. The degradation then continues throughout the branches and finally into the stem. From a distance, Ash Dieback is recognized by the haggard crowns, usually creating a sharp contrast against uninfected trees (image in the bottom right corner).
Ash Dieback was first reported in Eastern Europe during the mid-nineties and has since then rapidly spread throughout the European ashes' (Fraxinus excelsior) full natural range. In Sweden, the first symptoms were reported in 2001.
Breeding is a process which mainly consists of choosing the best candidates and cross these with each other to continuously improve your material for the next generation. This is nothing new, in fact is has been done since humans began farming and domesticating animals. For instance, corn and broccoli are two crops that have been cultivated in this way.
today is mainly used to increase wood production and to shorten the rotation time.
However, breeding trees for resistance against diseases is sometimes
feasible, if there is high genetic control of the desirable traits. In a study
from 2013, Lars-Göran Stener concluded that this indeed is the case for resistance
against Ash Dieback. This meant that there was a possibility to save the
Swedish ashes from extinction.
In the image to the left (below if you are reading this on your phone) Michelle Cleary is showing a promising candidate that seems healthy despite its’ infected neighbors. Perhaps this tree will eventually be the ancestor of a new generation of ashes?
"It will be necessary to select many ash tree candidates to obtain resistant clones while simultaneously considering other essential traits such as growth and stem quality (for forestry), and capturing the overall genetic variation within and among stands."
- Stener (2018)
Learn more about Ash dieback and breeding through the links below:
Timmerman, V., Borja, I., Hietala, A.M., Kirisits, T., Solheim, H. 2011. Ash dieback: pathogen spread and diurnal patterns of ascospore dispersal, with special emphasis on Norway. EPPO Bull. 40, 14-20.