Microbial colonisation of pruning wounds with particular reference to oak, Quercus robur.

A study of the microorganisms colonizing pruning wounds on mature oaks (Querous robur) has been made. The wounds were approximately 8" diameter and the type likely to occur on trees of amenity value in parklands and similar sites, where large limbs have been removed due to their being unsafe, diseased of causing obstruction. There would appear to be a definite succession occurring on oaks. In the initial stage there was a deep blue green discolouration, primarily of the sapwood. Organisms consistently isolated at this stage included species of Penicillium, Aureobasidium, Cladosporium, Trichoderma, Botrytis, Epicoccum, Bacillus and a range of Cram-negative rods. These pioneer colonists ae assumed to have originated from the air. They were characteristic of both the heartwood and sapwood and were isolated from both surface and sub-surface samples. After one month, sporing fungi were visible on the wound face and in some cases associated with intense blusing and bleeding of the exposed face. Successional changes followed the establishment of pioneer celenists and after two months species of Graphium and Phialophora became more prevalent. The next organisms to appear included species of Paecilomyces and representatives of the Sphaeropsidales and Mvcelia Sterilia, Basidiomycetes, particularly Stereum hirsutum did net appear until the wound was 10 months old. Spores of S. hirsutum have been shown to germinate well on elder wound tissue (79% germination rate) but poorly on freshly exposed wound surfaces. Bacteria were cultured frequently from all ages and types of wounds. The steroscan was usod in the microscopic examination of wound tissue. Evidence has been presented for the presence of bacteria, soft rot, white rot and broun rot fungi, and their effects on the tissues. The isolation and Stereoscan work support the idea that non-hymenomycetous fungi and bacteria precede Hymenomycetes in the colonization of pruning wounds on oaks