The Use of Gas-Sensor Arrays in the Detection of Bole and Root Decays in Living Trees: Development of a New Non-invasive Method of Sampling and Analysis

Abstract

Wood rot is a serious fungal disease of trees. Wood decay fungi penetrate and gain entry into trees through pruning cuts or open wounds using extracellular digestive enzymes to attack all components of the cell wall, leading to the destruction of sapwood which compromises wood strength and stability. On living trees, it is often difficult to diagnose wood rot disease, particularly during extreme weather conditions when trees can fail, causing tree parts to fall onto people and property. Today, tree stability evaluation and inner decay detection are performed visually and by the use of commercial instruments and methods that are often invasive, time-consuming and sometimes inadequate for use within the urban environment. Moreover, most conventional instruments do not provide an adequate evaluation of decay that occurs in the root system. A long-term research project, initiated in 2004, was aimed at developing a novel approach for diagnosing inner tree decays by detecting differences in volatile organic compounds (VOCs) released by wood decay fungi and wood from healthy and decayed trees. Different commercial electronic noses (ENs) were tested under laboratory conditions and directly in the field, on healthy and artificially-inoculated stem wood chips, and root fragments. The first stage of the research was focused on testing different commercially available electronic noses (e-noses) for the capabilities of discriminating between different strains and species of wood decay fungi as well as sapwood belonging to different tree species. In the second stage, sapwood of different tree species was artificially inoculated with decay fungi to test the diagnostic ability of the e-noses to detect differences in aroma bouquets emitted by healthy and inoculated woods. Root fragments were then inoculated with specific root decaying fungi and incubated under different types of soils to assess whether soil odors could influence the ability of the e-nose to discriminate between non-inoculated and diseased root fragments. For the final stage, soil air was evaluated for the presence of VOCs released by root-decaying fungi on diseased standing trees cultivated in the urban environment