Detectability of wood decay caused by Ustulina deusta in comparison with other tree-decay fungi.
Two devices were evaluated for the inspection of wood decay caused by Ustulina deusta (Hypoxylon deustum), the 'Metriguard' stress-wave time for decay detection, and the 'Fractometer', a sample corebreaking gauge, for measurements of the loss of strength. The stress-wave timer failed to detect decay caused by the fungus in naturally infected trees (Acer platanoides, Aesculus hippocastanum and Tilia platyphyllos) or inoculated wood blocks (T. platyphyllos and Fagus sylvatica), but detected decay in wood blocks from various tree species inoculated with the white-rot basidiomycetes Fomes fomentarius, Ganoderma pfeifferi (both on F. sylvatica), and Polyporus squamosus (on T. platyphyllos), and the brown-rot basidiomycete Laetiporus sulphureus (on Robinia pseudoacacia). The Fractometer showed large losses of strength in increment cores incubated with all the test fungi, including U. deusta, even at an early stage of decay. The patterns of cell-wall degradation, as shown by light microscopy, were consistent with the observed brittle nature of decay caused by U. deusta and with the results of testing the two devices. Both in naturally infected trees and in wood blocks, early degradation took the form of a soft-rot, with cavity formation in the S2 layer of the secondary cell walls. A white-rot supervened, but with prolonged persistence of a brittle, lignin-rich 'skeleton' that appeared to transmit stress-waves with little alteration in velocity.