Natural durability transfer from sawmill residues of white cypress (Callitris glaucophylla). - Part 2: Laboratory fungal bioassays
M A Powell, L M Stephens, L Francis, M J Kennedy
Extracts from sawmill residues of the naturally durable white cypress, Callitris glaucophylla were tested for fungicidal activity in a series of laboratory bioassays. The effects of different extraction solvents, techniques and sources of material on the biocidal efficacy of the resultant extracts were evaluated. Soil jar decay tests were used initially however, contractual time constraints necessitated the development of a more rapid screening technique. A modified sapwood agar media was developed and found to be suitable for testing the extracts. It could be applied to other non-diffusible wood preservatives. Ground white cypress sapwood was impregnated with a range of concentrations of various extracts and gamma irradiated. The treated sterilised sawdust was suspended in water agar. The media were inoculated with a white rot, Lopharia crassa, or a brown rot fungus Polyporus verecundus. Growth of the isolates was monitored for four weeks, enabling dose responses to be accurately determined. Methanol was determined to be the most effective extracting solvent, and toxic threshold values of the methanol extracts were estimated. Fractions of the total extract were also compared. Most fungicidal activity was found in the most abundant fraction, which contained significant proportions of terpenes and other non-polar, low boiling point compounds.
Keywords: SAWMILL RESIDUES; WHITE CYPRESS; CALLITRIS GLAUCOPHYLLA; BIOASSAY; EXTRACTS; SOIL JAR DECAY TEST; SCREENING TECHNIQUE; WHITE ROT; LOPHARIA CRASSA; BROWN ROT; POLYPORUS VERECUNDUS; METHANOL EXTRACTS