Bioincising

Norway spruce (Picea abies Karst.) and silver fir (Abies alba Mill.) are the two quantitatively most important tree species in Switzerland accounting for about 63% of the wood stock in the Swiss forests. As durable and local product, both species are widely used in building despite the fact that spruce and fir wood possesses a small natural durability. In addition they are very difficult to soak with wood protective products. The consequence is poor resistance to weather condition and important cost to both protect and maintain their suitable aspect. The loss of permeability of the heartwood is due to the closure of the pits, which are small openings through the cell walls enabling water exchange between adjacent cells. As the wood is maturating from sapwood to heartwood the pit membranes are irremediably closed.

To make the different protective products penetrate in the wood, vacuum/pressure cycles are used routinely with good results. But this method is time and energy consuming and many attempts have been made to try to enhance directly the permeability of the heartwood. Mechanical methods like incising or perforating have been tried, but they change the esthetical aspect of the wood surface and are as a consequence not suitable for a whole range of applications. The use of wood degrading bacteria or enzymes mix did not succeed either due to inconsistent pit opening and alteration in the mechanical resistance properties of wood.

A new very promising approach would be to use the wood degrading white rot fungus Physisporinus vitreus. This fungus has a particular wood colonising strategy. It first penetrates in the cells by re-opening the pits and only in a second stage starts to degrade the cell walls themselves. It is the perfect tool to enhance the permeability of the wood by re-opening the pits without changing its aspect and mechanical properties. Preliminary results have shown that the permeability was significantly increased after treatment with P. vitreus. Nevertheless to be able to use it in an industrial process it is necessary to obtain information on the growth parameters and requirements of the fungus. The aim of the presented work is to study the growth parameters in order to produce enough biomass of fit fungus to treat wood pieces in an industrial process. The growth parameters need in a second step to be optimised for efficient, rapid and even wood colonisation.