Common Decay Micromorphology “Anomalies” Challenge Current Decay Classification

IRG/WP 06-10578

R Wakeling

Decay micromorphology was studied systematically for diversely preservative treated Pinus radiata and Fagus sylvatica 20 x 20 x 500 mm stakes across 13 in-ground field test sites, during a 6.5 year exposure. New insight into the micromorphology of the early stages of decay enabled new and more detailed interpretation of the mechanism of their formation and suggested that current decay classification lacked sufficient robustness to accommodate common decay types encountered in field-exposed wood. Decay fungi that bypass the decay resistant S3 layer, producing multi-branched hyphae that collectively erode the S2 layer in a fashion similar to simultaneous white rot, forming a “super-cavity” under an overlying lumen wall, were very important in preservative treated beech fibres and pine tracheids. Whilst some of the micromorphology associated with this type of decay has been reported as diffuse type 1 soft rot, its significance has been largely overlooked. Results suggested that several important decay types have been overlooked or misinterpreted because their early defining features are easily masked by later features. This is particularly important for early cavitation decay that forms near or at the S3-S2 interface, and where the overlying lumen wall quickly disintegrates, has been sloughed off during sectioning or has been overlooked in low resolution light microscope micrographs. It is suggested that this has resulted in misinterpretation of cavitation decay types as erosion (Corbett’s type 2, erosion). Use of transmission electron microscopy (TEM) for examining decayed wood has relied heavily on transverse sections or use of high magnification, both of which would mask critical diagnostic features such as intact lumen wall in combination with longitudinally sectioned hyphae both of which are needed for diagnosis.


Keywords: decay micromorphology, white rot, soft rot, field tests, Pinus radiata, Fagus sylvatica.

Conference: 06-06-18/22 Tromsoe, Norway


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