Stem canker diseases of eucalypts in Tasmania

In order to evaluate the range of stem canker fungi in natural eucalypt forest and plantations in Tasmania, a systematic survey was conducted. A total of 210 samples representing 30 fungal species were collected. The three species most frequently encountered were Endothia gyrosa, Cytospora eucalypticola and Valsa ceratosperma. Ten of the fungal species detailed in this survey were newly published and five were reported for the first time in Australia. Pathogenicity studies were conducted with 11 fungal species collected from the survey. Three species (E. gyrosa, Phoma sp. and Seiridium eucalypti) could cause significant cankers on both E. nitens and E. globulus. Influences by host species, provenance, age, vigour and bark type on canker development are discussed. The incidence of canker is higher in rough-barked E. nitens compared to smooth-barked trees. Longitudinal cracking in rough bark provides natural infection courts. However, once infected artificially, smooth-barked E. nitens is more susceptible than rough-barked. This susceptibility is attributed to the anatomical structure of smooth bark facilitating post-infection penetration. A high incidence of severe E. gyrosa cankers was observed in 1993 at Tewkesbury (northwestem Tasmania) within a vigorously growing plantation of mixed (smooth or rough barked) provenances of 16 yr old E. nitens. This observation initiated an in-depth investigation of E. gyrosa. Stem inoculations with isolates of E. gyrosa originating from different locations across Australia showed that all can infect E. nitens and E. globulus. However, isolates from Tasmania, Victoria and Western Australia were generally more aggressive than those from the Australian Capital Territory and New South Wales. Endothia gyrosa isolates from Australia and overseas were compared. Four main types of colony morphology were recognised among 133 isolates based on the colour and density of the vegetative mycelium. Vegetative incompatibility was detected using a pH amended medium. Sixteen isolates from different origins in Australia, South Africa, North America and Europe were grouped into 9 vegetative compatibility groups with this method. There was correspondence between the grouping of these sixteen isolates as determined by colony morphology and vegetative compatibility and those revealed by DNA polymorphisms in RFLP and RAPD analyses. Overseas and Australian isolates appear closely related. Within Australia isolates from as geographically distant locations as Western Australia and Victoria were grouped together. The significance of observed levels of intraspecific variation in E. gyrosa is discussed. The potential threat of canker fungi, especially E. gyrosa, to the plantation forestry is reviewed.