Accelerated detection of brown-rot decay: Comparison of soil block test, chemical analysis, mechanical properties, and immunodetection

Abstract

Early detection of wood decay is critical because decay fungi can cause rapid structural failure. The objective of this study was to compare the sensitivity of different methods purported to detect brown-rot decay in the early stages of development. The immunodiagnostic wood decay (IWD) test, soil block test/cake pan test, mechanical property tests, and chemical analysis were evaluated in southern yellow pine blocks and stakes exposed to Postia placenta for 5 weeks. The IWD test was 100 percent positive in blocks after 5 days of incubation; similarly, IWD was 100 percent positive in stakes after 3 days. Weight loss was not accurate for measuring decay in stakes using the cake pan method, but significant weight loss (18%) occurred in blocks after 4 weeks of exposure to the fungus in soil block tests. Maximum compressive strength (MCS) and modulus of elasticity (MOE) were reduced 21 and 13 percent, respectively, in blocks exposed to the fungus for 2 weeks. In stakes, MOE and modulus of rupture were reduced 9 percent and 19 percent, respectively, after 4 weeks of exposure. Arabinan, xylan, and rhamnan decreased rapidly in blocks, exceeding 30 percent after 4 weeks of exposure. In stakes, only galactan was decreased beyond 30 percent after 4 weeks. Sample size and shape was a significant factor in successfully detecting early stages of brown-rot decay in laboratory tests. Blocks fostered rapid colonization in soil block tests, and most methods tested were able to detect the fungus sooner in blocks than in stakes. The IWD test was the most rapid method of detecting P placenta (from 3 to 5 days), followed by reduction in MCS in blocks.