A recent question concerning identification of wood-rot fungi seemed to be an interesting topic for many of our readers. The wood rot on the tree was obvious by the rotted, sloughed bark; the decaying wood at the base of the tree; and the oozing sap. Laboratory personnel often prepare cultures from wood that is thought to be infected with a pathogen. In most cases, we try to isolate and identify any fungal pathogens present in the sample. Many fungi develop hyphae in the cultures and with some time form spores or fruiting bodies that allow us to make a positive identification. The Dutch elm disease fungus is a good example. The question posed to the Plant Clinic was whether we could isolate and identify the wood-rot fungi in the same manner.

Most wood-rotting fungi have a vegetative form that grows on and in the wood. The vegetative stage (hyphae) does not differ much with each wood-rotting fungus, so isolating this stage is not very helpful. We could isolate the hyphal phase, inoculate some wood, incubate this wood at the proper environment (often unknown), and wait for several months for the fruiting body to form. Because wood rots are often inhabited by secondary wood-rotting fungi, we could not be certain we had isolated the primary cause. The whole procedure is not practical or dependable. We need the fruiting bodies to positively identify these fungi. The fruiting bodies are the conks (basidiocarps) that form on the trunk or branches. Refer to RPD No. 642 for details.