ASH DIEBACK

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.

SYMPTOMS:

Nedan visas typiska tecken på askskottsjuka. Infektionen påbörjas oftast genom bladenÇ, då sporerna från H. fraxineus tar sig in via bladnerverna. Nedbrytningen fortsätter sedan i grenar och slutligen stammen. På håll känns askskottsjukan igen genom de slitna kronorna (bild nederst till höger) vilka blir en stark kontrast mot sina eventuellt friska grannar.

SPREAD:

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

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. Tree breeding 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?

READ MORE

Read more about ash dieback and breeding through the links below.
"Skogforsk on ash breeding"
PDF ASH DIEBACK
"Ash dieback – threat and hope"
“It will be necessary to select many ash candidates to produce resistant clones. At the same time, traits associated with forestry must be favored, as well as the genetic variation within and between ash stands.” – Stener (2018)

REFERENCES:

Cleary M R, Nguyen D, Marčiulynienė D, Berlin A, Vasaitis R, Stenlid J. 2016. Friend or foe? Biological and ecological traits of the European ash dieback pathogen Hymenoscyphus fraxineus in its native environment. Scientific Reports.

Stener, L. G. (2013). Clonal differences in susceptibility to the dieback of Fraxinus excelsior in southern Sweden. Scandinavian Journal of Forest Research, 28(3), 205-216.

 Stener, L. G. (2018). Genetic evaluation of damage caused by ash dieback with emphasis on selection stability over time. Forest ecology and management, 409, 584-592.

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.