Action of Soft Rot- and White Rot Fungi on Partially Delignified Softwoods

Abstract

Fourty-four species of softwoods were partially delignified with acidified sodium chlorite for 6 hours at 40℃ and exposed to a soft rot fungus, Chaetomium globosum KUNZE, for 8 weeks at 28℃. The weight losses after the chlorite treatment considerably varied with species. The lowest weight loss was 1.6 % for Chamaecyparis obtusa and the highest was 21.9 % for Larix gmelini. The weight losses after the exposure to Ch. globosum noticeably increased in proportion to the degree of delignification. The highest weight loss was 58.2 % for Picea glehnii and the lowest was 6.2 % for Chamaecyparis obtusa. Furthermore, the pattern of acceleration of wood decay by the chlorite treatment has been studied for two softwoods and one hardwood, with reference to the decrease of total lignin content, using Ch. globosum and a white rot fungus, Coriolus versicolor QUEL. The results showed that the effect of delignification was positively observed in all woods for both fungi but considerably varied with wood and fungal species. In the case of Pinus densiflora, the maximum level of wood decay was reached at about 43 % of delignification for Ch. globosum and at greater stage of delignification for Co. versicolor. In Cryptomeria japonica, the maximum level was at 50 % or more for Ch. globosum and at about 18 % for Co. versicolor. Maximum levels in both woods for Ch. globosum were higher than those for Co. versicolor, in spite of lower attacking capacity of the former on original woods. In Fagus crenata, highly susceptible to both fungi, acceleration was not greater than in the two softwoods.