Fungal-termite associations in the natural resistance of selected eucalypt timbers
D B A Ruyooka
Butt billets of Eucalyptus regnans F. Muell., Eucalyptus grandis W. Hill ex Maiden, and Eucalyptus camaldulensis Dehnh., showing no visible signs of decay, were examined for the presence of fungi in outer, middle and inner heartwood. Fungi obtained in pure culture were characterized. Eucalyptus regnans yielded Cytospora eucalypticola van der Westhuizen, Trichoderma harzianum Rifai and Penicillium spp.;·Eucalyptus grandis yielded Pesotum sp., Acrodontium sp. and Penicillium spp.; and Eucalyptus camaldulensis yielded only Penicillium spp. The natural termite resistance of the same billets was investigated, following decay (12 weeks) by brown-rot Gloeophyllum trabeum (Pers. ex Fr.) Murr., white-rot Fomes lividus (Kalch.) Sacc. and soft-rot Chaetomium globosum Kunze. Blocks were exposed to the termite Nasutitermes exitiosus (Hill) (Termitidae) under laboratory and field conditions to determine if there were significant, quantitative differences in (1) fungus-infested and uninfested blocks, (2) blocks containing living or dead fungus, (3) types of radial heartwood, and (4) species of timber. Clearly fungus-infested wood was preferred to the uninfested by Nasutitermes exitiosus, and dead fungus in wood to the living. Further there was pronounced radial variability, and timber species were also markedly different, although these differences could not be measured, for the presence of strong interactions. The interactions involved species of fungus and timber, species of fungus and type of radial heartwood, condition of fungus (dead or alive) and species of timber, and species of timber and radial heartwood. In the case of tyndallised (at 70°C) timber exposed to decay fungi only, similar interactions, involving species of fungus and timber, and species of fungus and type radial heartwood, were also evident. The interactions implied that fungal or termite resistance of wood was not only influenced by the inherent properties of a timber species, but also by type of heartwood, fungal species and condition of the fungus involved.