A wood soil contact culture technique for laboratory study of wood-destroying fungi, wood decay and wood preservation

Leutritz, J.

Bell Syst. tech. J 25(1): 102-135


DOI: 10.1002/j.1538-7305.1946.tb00897.x
Accession: 013627416

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The soil-contact method heroin described was found to be a valuable laboratory adjunct for the study of fungal destruction of cellulose and wood and for the determination of the efficacy of wood and cellulose-preservatives . Top soil with a 20 to 25 per cent, moisture content on a dry-weight basis, used as a substratum for decaying pine wood blocks, proved to be an excellent means of controlling the. moisture content of the wood during the decay process. The optimum moisture content for the initiation of wood decay was fibre saturation. The initial water content of the wood remained constant during disorganization through maintenance of a constant volume of the wood structure, notwithstanding the loss of wood substance. Investigation of the addition to the soil of various combinations of nutrients and ' nutrilitea' (compounds necessary to fungus nutrition, e.g., vitamins, growth substances, and mineral salts, as defined by R. J. Williams in Science, N.S., xvii, p. 607, 1928) showed the importance of these materials in decay. The need for nitrogen by fungi causing destruction of cellulose, demonstrated by Schmitz and Kaufert, was confirmed. A comparison of the results obtained with, nutrient artificial soils and an average top soil indicated the possibility of using the former in the contact test method. The optimum temperature for Poria incrassata, Polyporus vaporarius, P. microspora, and B(ell) T(elephone) L(aboratories) U-ll was 26 degrees to 28 degrees C., but Lentinus lepideus, Lenzites sepiaria, and L. trabea (BTL/U-40) caused considerable decay at 35 degrees . Merulius lacrymans, on the other hand, was responsible for an average reduction in weight of 34 per cent. after six months at 21 degrees compared with only 7 per cent. at 26 degrees to 28 degrees . Decay occurred over a wider temperature range and was much more uniform and rapid in soil-contact than in Petri-dish tests or other laboratory methods or in field trials. Petri-dish assays of preservatives were often misleading. In general, higher retentions were necessary to prevent decay than were indicated by this technique, but occasionally a material giving poor results in the Petri-dish trials acted as a satisfactory preservative of cellulosic derivatives both in soil-contact and field tests. Comparisons between the soil-contact assay and field trials of wood preservatives corroborated the closer approximation of the former to the optimum conditions for decay and the consequent exceptional severity of the tests thereby imposed on the experimental products. The soil-contact method may, in short, be applied to a wide range of materials, including leather, cotton, felt, paper, and jute with the assurance that any preservative preventing decay by this laboratory test, and permanently retained, will be effective under any climatic conditions.