11. May 2020

WOOD: extracts from the tree of heaven as a biological wood preservative

The tree of heaven (Ailanthus altissima) is a deciduous tree in the family Simaroubaceae. It originated in Asia and was brought to Europe as an ornamental plant in around 1740. It is characterized by a high tolerance of salt, aridity, herbicides and airborne pollutants. However, it also has considerable drawbacks: It is an invasive plant that is spreading globally and forcing out other species of tree, particularly in national parks. In its branches, leaves and especially bark the tree of heaven contains bitter substances, called quassinoids, that protect it from predatory herbivores and pathogens, but also prevent other species of tree from growing beside it. These substances could be of interest as a natural wood preservative.

As part of a bilateral project run in conjunction with the Austrian forestry commission Österreichische Bundesforste (ÖBF) a number of bioactive substances taken from extracts of the tree of heaven were tested for their inhibiting effect on wood-destroying fungi, especially white and brown rot fungi from the Basidiomycota phylum.

Once the extraction process from tree of heaven bark had been optimized to attain the greatest possible amount of target substances in the extract, their antifungal properties were tested in microbiological inhibition trials. A long-term test was then conducted using standardized testing procedures (EN 113) to determine the efficacy of the extractives obtained in the prevention of wood-destroying Basidiomycota on small logs.

The test showed that the so-called ailanthones, which are classed among the triterpenoids, acted with particular bioactive efficacy on defined test fungi such as Coniophora puteana and Merulius himantioides. The results suggest that the extracts obtained from the tree of heaven have potential as a biological wood preservative to combat fungal organisms.

Further tests are planned which will include other species of fungus (e.g. soft rot fungi and blue stain fungi) to determine the potential antifungal action of tree of heaven constituents, and those of other invasive plants such as the robinia, on a wide range of fungi.


Photo: Production and application of tree of heaven bark extracts to combat wood-decaying white rot fungi (source XXLRay)
(c) Wood K plus, Title: iStock