Wood science seminar: ”Mechanisms of brown-rot fungal attack on wood”
Welcome to a wood science seminar on ”Mechanisms of brown-rot fungal attack on wood” by invited lecturer Dr. Roger Rowell, Professor Emeritus, University of Wisconsin, Madison, USA. See attached abstract.
Tid: Ti 2019-10-08 kl 15.00 - 16.30
Föreläsare: Dr. Roger Rowell, Professor Emeritus, University of Wisconsin
After the seminar there will be some time for mingle and some minor snacks and liquid refreshment.
Register by e-mail to firstname.lastname@example.org no later than Monday 7 October
While brown-rot fungi only accounts for about 6% of the total fungal population, it is the one that causes the most damage especially in softwoods. There are many theories on the mechanism of the attack of brown-rot fungi on softwoods. Theoretically, the first step may be a favorable environment. Fungi need an environment that is conducive to their survival: temperature, moisture, pH, and toxicity. If the temperature is too high or too low or if the wood is too wet or too dry, or if the pH is too high or too low, the fungi cannot colonize. And, if there are toxic chemicals in the wood, the fungi cannot survive. If the environment is favorable, the fungal attack starts.
We can measure loss of mechanical properties such as MOR, MOE, hardness, etc in a biological test using a brown-rot fungi and find that these properties have been greatly reduced with very little weight loss.
In that same test, we observe a drop in the pH as the fungus colonizes. The hyphae of a brown-rot fungus must detect a source of nutrition in the wood it has come into contact with in order to survive. Early in the attack is oxidation and rearrangement of lignin. No lignin is lost at this point but it is known to be somewhat oxidized and condensed. At this stage, the fungus is undergoing gene expression to start the production of cellulosic enzymes.
Since the result of early brown-rot degradation is a loss of cell wall carbohydrate polymers (mainly the hemicelluloses), it is logical to assume the first degrading reaction is low molecular weight non- enzymatic system. This first reaction is the generation of a peroxide/ferrous ion and a hydroxyl radical chemical system (Fenton 1894) that depolymerizes the structural polysaccharides in the cell wall matrix resulting in strength losses. The hemicelluloses and the cellulose polymers start to degrade and major strength losses are observed.
In each of these theoretical steps, moisture is involved. Moisture is part of the porous surface, it is needed for the production of oxalate and its movement in the Fenton chemistry [Fe++ + H2O2 + H+ → Fe+++ + OH (hydroxyl radical) + H2O], necessary at a glyosidic bond for hydrolysis, needed for enzyme activity, generated by the fungus as a by-product in digestion, and, finally, needed to move soluble sugars. All of these are steps involve wet chemistry and the question is how much moisture is needed, where does it come from and where is it located in the cell wall? When moisture in the cell wall is reduced by one of several chemical modification reactions, the equilibrium moisture content is reduced and resistance to decay is greatly improved? Is restricting moisture to the fungus the key to the mechanism of brown-rot attack on wood?
About Roger Rowell:
Roger M. Rowell has an education background in the areas of chemistry, mathematics and biochemistry, achieving a PhD in 1965 in biochemistry at Purdue University in West Lafayetta, Indiana. His research specialties are in the areas of carbohydrate chemistry, chemical modification of lignocellulosics for property enhancement, water quality and sustainable materials. He is by no doubt an “icon” within the field of wood science, especially known for pioneering research, industrial development and innovations related to wood acetylation in the 1980-ies together with a Swedish research group at Chalmers University. He is also known for being an inspiring lecturer, also with a talent for popular science presentations. He has been a visiting scholar in Japan, Taiwan, Sweden, Mexico, the United Kingdom, New Zealand, and China.
Dr. Rowell retired as a senior technical pioneering scientist after 41 years at the USDA (the United States Department of Agriculture) Forest Service, Forest Products Laboratory, Madison, Wisconsin. He also retired, at the same time, from the University of Wisconsin, Madison, after 35 years and is now a Professor Emeritus. He has taught courses in wood chemistry in several countries and has presented many lectures at international and national scientific meetings. He is a fellow of the International Academy of Wood Science and the Chemical Society, Division of Cellulose, Paper and Textiles. He has edited 11 books, and has over 350 publications and 24 patents. And finally, just to mention, he is still active.