Decay resistance of Togolese teak (Tectona grandis L.f) heartwood and relationship with colour

Togolese teak (Tectona grandis L.f) is highly resistant to pathogen attack, but variability in natural durability exists between trees of different ages, plantations and geographical zones. Therefore, further information concerning this parameter of wood quality is necessary; however, traditional testing methods are difficult and time-consuming to carry out. We tested the possibility of using colorimetry to determine durability in heartwood samples taken from a wide range of trees. Twelve hundred samples from 31 trees were exposed to four fungi: Pycnoporus sanguineus, Antrodia sp., Gloephylum trabeum, and Coriolus versicolor. Wood samples were grouped into three classes (inner, intermediate and outer heartwood). The colour parameters of each sample were then determined using the CIELAB (L*, a*, b*) system and results correlated with the %mass loss of wood after fungal attack. Tests showed that Antrodia sp. and C. versicolor resulted in <20% mass loss, whereas all samples were rated as durable or highly durable with regard to P. sanguineus and G. trabeum. Inner heartwood was found to be the most resistant to pathogen attack and outer heartwood the least. Measurements of colour showed that heartwood was lightest nearest the pith and darkness and redness increased towards the outer heartwood. Regressions of lightness with %mass loss in the durability tests were always highly significant, whereas a* and b* were not always significantly regressed with %mass loss. Therefore, the use of colorimetry as a tool to estimate short-term natural durability both rapidly and cheaply could be considered in the case of plantation grown teak wood.