Zq Yuan

Pathogenicity of fungi associated with stem cankers of eucalypts in Tasmania, Australia

Thirteen stem-infecting fungal species, 11 from Tasmania and 2 from other parts of southeast Australia, were tested for their pathogenicity on 12-month-old seedlings of Eucalyptus nitens and E. globulus. They were classified into three groups based on their ability to cause stem canker lesions following artificial inoculation: pathogenic species (Phoma sp., Endothia gyrosa, and Seiridium eucalypti), intermediate or weakly pathogenic species (Botryosphaeria sp., Seiridium papillatum, Pestalotiopsis neglecta, Zythiostroma sp., Ceuthospora innumera, Cytospora eucalypticola, and Wuestneia epispora), and nonpathogenic species (Dinemasporium strigosum, Seiridium unicorne, and Harknessia aff. eucalypti). The potential threat of canker fungi, especially Endothia gyrosa, to plantation forestry in Australia is discussed.

Investigation of fungi associated with stem cankers of eucalypts in Tasmania, Australia.

A survey of stem fungi and associated canker diseases in eucalypts in natural forest and plantations was conducted in Tasmania. A total of 209 samples representing 29 fungal species was obtained. Thirteen of the fungal species detailed in this survey have not been described or previously reported in Australia. The three species most frequently encountered were Endothia gyrosa, Cytospora eucalypticola and Valsa sp., constituting 23.9%, 20.6% and 12.9%, respectively, of the 209 collections. They were ubiquitous, with each species found on more than ten eucalypt species. Fungal species with low incidence but associated with severe cankers were Harknessia cf. eucalypti, Phoma sp., Seiridium eucalypti and Zythiostroma sp.

The pathogenicity of isolates of Endothia gyrosa to Eucalyptus nitens and E. globulus

A severe epidemic of Endothia gyrosa in a plantation of Eucalyptus nitens at Tewkesbury in Tasmania prompted a comparison of the pathogenicity of isolates from this site with that of isolates from elsewhere in Tasmania and mainland Australia. Sixteen isolates were artificially inoculated on 12-month-old seedlings of two major plantation species, E. nitens and E. globulus. The majority of isolates produced lesions on both host species that were significantly different in size to those in non-inoculated seedlings and were not callused-over at 7 months after inoculation. Seedling mortality was negligible. Certain isolates originating from various regions in mainland Australia and from the Tewkesbury site appeared more pathogenic although differences in lesion size between isolates was not always significant. Only one out of seven isolates from Tewkesbury demonstrated significantly higher levels of pathogenicity than all other isolates although there was a trend for isolates from this site to cause greater lesions in size. It is, however, unlikely that the epidemic caused by E. gyrosa at Tewkesbury, even though of far greater impact than previousiy observed on plantations in Australia, is solely the consequence of more pathogenic strains. This conclusion does not exclude the possibility that more pathogenic strains of an opportunist pathogen such as E. gyrosa could have played some determinant role in epidemic development.

Cryptosporiopsis leaf spot and shoot blight of eucalypts

Cryptosporiopsis eucalypti has been associated with foliar disease of eucalypts in many parts of the world, especially in South-East Asia where Eucalyptus camaldulensis can be severely affected. In a field trial in southern Vietnam of 150 open-pollinated families of seven tropical provenances of E. camaldulensis, C. eucalypti was the main pathogen associated with leaf blight and crown dieback. Variation in susceptibility to foliar disease occurred at the family, provenance and sub-species levels offering excellent opportunities for selection of resistant trees. Pathogenicity tests using seedlings have shown that the fungus can infect stems as well as leaves. Stem inoculation may offer opportunities for rapid screening for resistant germplasm, but a connection between the results of such tests and field performance has not been made.

Harknessia species occurring on eucalypt leaves in Tasmania, Australia.

Three Harknessia species are reported on eucalypt leaves from Tasmania, Australia. Harknessia hawaiiensis is a new record for Australia and H. victoriae for Tasmania. Harknessia tasmaniensis is described and illustrated as a new species.

First report of Gloeosporidina sp. isolated from lesions on shoots and leaves of Eucalyptus nitens and E. globulus in Australia.

A mitosporic fungus with small conidia was frequently isolated from blighted shoots and leaves of young plantation trees and nursery seedlings of Eucalyptus nitens and E. globulus in Tasmania. Lesions on these shoots and leaves are purple to light brown, becoming necrotic with well-defined margins. The fungus is characterized by having acervular conidiomata, cylindrical to lageniform monophialidic conidiogenous cells, and spheroid to pyriform conidia that are hyaline, aseptate, and often produced in chains. The morphological characteristics fit the published description for the genus Gloeosporidina. This is the first record of a member in the genus from Australia and the first time a Gloeosporidina species has been found on eucalypts.

Pseudophacidium diselmae sp. nov. isolated from stem cankers on Diselma archeri in Tasmania, Australia

Fungi associated with stem cankers on Diselma archevi in central Tasmania were investigated. Three Ascomycetes (Massavia sp., Trernatosphaevia sp. and Pseudophacidium sp.) were observed on stems with canker symptoms. The Pseudophacidium species was the most consistently isolated fungus from canker tissue and is proposed as P. diselnzae sp. nov

A sclerotium-forming strain of Botrytis cinerea associated with shoot blight of Eucalyptus globulus in Tasmania

A strain of Botytis cinerea which readily formed sclerotia in vivo and in vitro was associated with shoot blight in young plantations of Eucalyptus globulus in Tasmania.