Abstract: A method is described of obtaining cellulase deficient strains which have great ability to degrade lignin at the same time. The method comprises crossing a homokaryotic cellulase deficient mutant of a white-rot fungus having a full sexual cycle with a homokaryotic strain of the same fungus, this strain having great lignin degrading ability. Strains are subsequently selected that have great lignin degrading ability in combination with cellulase deficiency. A suitable white-rot fungis is Phanerochaete chrysosporium. The crossings are suitably performed for a plurality of generations. The strain of white-rot fungus obtained is used for delignifying lignocellulosic material.

Abstract: A method of producing cellulose pulp from a starting material containing lignin and cellulose, particularly from wood, wherein the starting material is treated with an organism capable of forming lignin-decomposing enzymes under conditions such that the lignin is substantially decomposed without appreciably affecting the cellulose.