Assessment of the mechanical properties of lodgepole pine in the incipient stage of decay by a white-rot fungus

This study quantified the effects of volume and stage of a wood decay fungus (Phellinus pini (Thore Lloyd) on the mechanical strength of lodgepole pine and its impact on the current standard of visual stress grading. To improve detection and identification of decay fungi at the species level during the incipient decay stage, a fungal ribosomal DNA assay was designed. An effective extraction method for isolating fungal DNA from wood also was developed by integrating the glass bead system, organic solvents and an extraction buffer.; A Basidiomycete, Phellinus pini and an Ascomycete, Byssochlamys nivea were successfully identified from fungal cultures by directly sequencing with ITS-1F (specific for higher fungi) and ITS-4 (universal primer) primers. This study also demonstrated that direct sequencing can correctly identify these decay fungi, avoiding incorrect identification due to morphological variation within and between these species.; The average percentage reduction in modulus of elasticity (MOE) and modulus of rupture (MOR) were significantly affected by decay volume and discoloration, but the interaction of decay volume and discoloration had little effect on these properties. The average percentage reduction of specific gravity was affected by only discoloration, while the average reduction percentage of compression parallel to the grain increased significantly with increased decay volume. The reduction of MOR increased more rapidly than did the reduction in MOE. MOR showed an average maximum reduction of 34% at the combination of high discoloration and 67–100% decay volume while MOE exhibited a 20% average maximum reduction. Compression parallel to the grain displayed a 15% average maximum reduction at 67–100% decay volume.; The results indicate that the maximum 34% reduction of MOR corresponds to the maximum allowable reduction of MOR of No 1. structural grade for beam-stringers in the Western Wood Products Association (WWPA) grading rules. The strength reduction of MOR is large enough to be of serious concern. While, the reductions in MOE and compression parallel to grain do not impact the current visual stress grading rules, the reduction in MOR calls for further investigation into potential impact on grading rules.