A new study: Inonotus obliquus conks growing on Alnus incana has remarkable properties

Foto: Ahto Täpsi
Inonotus obliquus on a grey alder

A study led by researchers of the Estonian University of Life Sciences demonstrated that Inonotus obliquus, parasitizing on Alnus species, has comparable properties to the fungus growing on Betula species.

Inonotus obliquus is the fungus known to parasitize on Betula. I. obliquus grows in the Northern Hemisphere and belongs to the family of Hymenochaetaceae in the order Hymenochaetales and causes stem rot on several broadleaved tree species.

In Estonia, the fungus grows primarily on Betula pendula, Betula pubescens, Alnus incana and Alnus glutinosa. Sterile conks of I. obliquus contain bioactive compounds known to have anti-cancer effects, e.g. against proliferation of cells of leukemia and lung and colon adenocarcinoma, hepatocellular carcinoma of the liver, oral epidermoid carcinoma and prostate cell carcinoma.

The bioactive compounds extracted from the I. obliquus, especially betulin, betulinic acid and inotodinol inhibit the development of cancer cells. Previous studies have concentrated on the I. obliquus on birch trees, but it is not known whether the conks parasitizing on other tree species can offer equivalent properties.

As known, the current study is the first to determine the bioactive compounds of the I. obliquus parasitizing on alder species. The results demonstrate convincingly that conks of I. obliquus parasitizing on A. incana, which is growing well in Estonia, contain betulin, inotodiol and lanosterol to a similar extent as I. obliquus on B. pendula.

Surprisingly, the A. incana conks contained even up to 30 times higher betulinic acid than the conks parasitizing on B. pendula, 474–635 µg/g and 20–132 µg/g, respectively. The conks parasitizing on grey alder contained more beta-glucans, polyphenols and flavonols compared to the conks on silver birch. However, betulinic acid, betulin and inotodiol are more important in terms of anti-cancer effect.

Therefore, there is no substantive difference whether I. obliquus grows on a grey alder or a silver birch. However, further research is still needed to establish the potential effect of I. obliquus conks on alder on various cancer cell lines. Preliminary research also suggests the possibility that I. obliquus may have other valuable properties, such as effects on the immune system.

So what is the importance of the research for forestry and landowners? Alder is growing well in Estonia, for example, A. incana dominated the stands cover by approximately 9%, and of the private forest area, A. incana covers 14.1%. It would increase the still comparatively low economic value of grey alder generally considered suitable mostly for firewood by cultivating this host I. obliquus and would offer landowners, especially small landowners, an opportunity to earn.

The article is not calling for mass inoculation of trees with a pathogenic fungus, the risks and best practices for inoculating trees need to be researched before a tree inoculation campaign, and only then one can proceed to cultivation. The study shows that grey alder is not a worthless tree species, but rather an important resource that can be valued in many ways.

The study was conducted by researchers from the Institute of Forestry and Rural Engineering at the Estonian University of Life Sciences, the Institute of Agricultural and Environmental Sciences, and the Institute of Pharmacy at the University of Tartu.

Article: Comparative Analyses of Bioactive Compounds in Inonotus obliquus Conks Growing on Alnus and Betula. R. Drenkhan, H. Kaldmäe, M. Silm, K. Adamson, U. Bleive, A. Aluvee, M. Erik, A. Raal.