Measuring the decay resistance of Scots pine heartwood indirectly by the Folin-Ciocalteu assay

Abstract

To exploit the variation in the natural durability of heartwood timber, screening of a large number of trees or timber is necessary. We suggest that the concentration of total phenolics, measured by the Folin–Ciocalteu (FC) assay, can be used to supplement or even replace in vitro decay tests for screening the variation in the resistance of Scots pine (Pinus sylvestris L.) heartwood timber against the brown-rot fungus Coniophora puteana (Schum. ex Fr.). We screened the juvenile heartwood of 520 Scots pine trees with the FC assay. Samples from 40 trees, with total phenolics concentrations ranging from 1.9 to 21.7 mg tannic acid equivalents (TAE)/g of heartwood, were subjected to an in vitro decay test. The correlation (r) between the total phenolics concentration and mass loss was –0.82 (p < 0.001) in the 7 week long decay test. The relationship was expressed with a linear regression equation: mass loss (mg/g) = 487 – 25 × concentration of total phenolics (mg TAE/g). This strong relationship could be exploited by replacing the decay test with the FC assay to more rapidly assess the durability of wood products.

The effect of brown-rot decay on water adsorption and chemical composition of Scots pine heartwood

“…The stand was established in May 1968 by planting 2-year-old, bare-root seedlings, managed in the same way as in normal commercial forestry, and thinned in 1997. A sample of 40 trees had earlier been selected from the stand (Harju and Venäläinen, 2006). The sampling followed a two-stage procedure.…”

“…(strain BAM Ebv. 15), for seven weeks (Harju and Venäläinen, 2006). The average mass loss of the samples was 22.5% (standard deviation 15.6%), which was determined on oven-dry (60…”

“…The FC assay was carried out as described in Harju and Venäläinen (2006). Tannic acid (Merck; 1.59446.0010) was used as a reference standard, and the results are therefore expressed as milligrams of tannic acid equivalents (TAE) per gram dry wood.…”

“…Heartwood contains compounds other than phenolic compounds, e.g. resin acids and sugars, which react in the FC assay (Harju and Venäläinen, 2006;Prior et al, 2005). However, we have used the expression "concentration of total phenolics" for the results of the FC assay.…”

“…Moreover, we investigated whether the change in the chemical composition of decayed wood distorts the negative correlation between the result of the Folin-Ciocalteu assay and the decay resistance (Harju and Venäläinen, 2006). The wood material covered a wide range of heartwood extractive concentrations and, accordingly, a wide range in the stage of decay attained in a 7-week decay test.…”