Oak Canker Research Articles

Identification and characterization of bacterial strains associated with diseased oak trees in Northern Iran

AbstractOak decline syndrome is characterized by periodic occurrences of decline and death of oaks over widespread areas. An outbreak of a new emerging disease on oak trees was reported in the Hyrcanian forest of Iran (Mazandaran and Golestan provinces) that showed stem bleeding and canker symptoms. Bacterial isolates were characterized through biochemical and physiological tests, protein electrophoresis, DNA fingerprinting (rep‐PCR, ERIC and BOX primers) and sequencing of 16S rRNA and MLSA (multilocus sequencing analysis) for housekeeping genes (gyrB, infB and atpD). A complex community of the genus Brenneria spp. (Brenneria goodwinii, Brenneria roseae subsp. roseae, Brenneria sp. and Brenneria nigrifluens) and a few isolates in the genus Gibbsiella were identified as major groups involved. Isolate differentiation was more accurate using concatenated partial gene sequences within the main groups. All bacterial isolates showed hypersensitivity reactions (HR) on Pelargonium leaves (Pelargonium × hortorum). Pathogenicity studies of different Brenneria and Gibbsiella strains revealed that they have potential to cause the disease in oak seedlings and devastating oak canker and stem bleeding symptoms in northern Iran. Due to the presence of several potentially pathogenic agent(s) associated with the oak decline, identification of the principal agent(s) is of major interest. To our knowledge, this is the first report of potentially pathogenic bacteria associated with oak bleeding and canker in Iran.

Species of Dendrostoma (Erythrogloeaceae, Diaporthales) associated with chestnut and oak canker diseases in China.

Dendrostoma was recently proposed in Erythrogloeaceae (Diaporthales, Sordariomycetes), with all known members recorded as being plant pathogenic on economically important tree hosts. During our collections of Dendrostoma species in China, mild to severe canker symptoms were observed on sweet chestnut (Castaneamollissima) and oak (Quercus spp.) trees. Dead and dying plant tissues exhibiting Dendrostoma canker symptoms were sampled for fungal isolation. A total of 37 Dendrostoma isolates were obtained and analysed using morphological characteristics and molecular data (ITS, LSU, RPB2, TEF1-α). Based on these data, 10 novel clades could be distinguished, which also proved to represent morphologically distinct species described here as Dendrostomaaurorae, D.castaneae, D.castaneicola, D.chinense, D.dispersum, D. parasiticum, D.qinlingense, D.quercus, D.shaanxiense and D.shandongense spp. nov. A key to species of the genus is also provided.

Two novel species of Cryphonectria from Quercus in China

Cryphonectria species associated with canker disease are presently difficult to identify, because of lack of ex-type cultures with molecular data and few distinguishable characters. During our survey about chestnut blight in western China, Cryphonectria parasitica was confirmed as the most important canker pathogen based on ten morphologically atypical isolates. Two novel species with orange stromata are introduced based on multigene sequence (ITS, TUB1, TUB2) analyses. This is the first study that has established the Cryphonectria species associated with oak canker in China using a multiphasic approach.

Botryosphaeriaand Related Taxa Causing Oak Canker in Southwestern Spain

Although root disease caused by Phytophthora cinnamomi is considered to be the most frequent and damaging disease associated with Quercus spp. decline in southwestern Spain, cankers commonly are observed on branches of declining Mediterranean Quercus spp. in this region. In surveys carried out in eight declining Quercus forests, strips of necrotic inner bark were common on diseased branches. Botryosphaeria stevensii, B. dothidea, and Diplodia sarmentorum consistently were isolated from these branches. Isolates of all three species caused cankers when inoculated onto excised Quercus branches. Inoculations on healthy branches in the field also induced canker development, but only B. stevensii caused lesions that girdled and killed the branches. The optimum temperature for in vitro growth of B. stevensii and B. dothidea was above 25°C, with slow growth at 35°C. In contrast, D. sarmentorum had an optimum temperature for growth of about 21°C, and did not grow at 35°C. The common occurrence and wide distribution of these pathogens, their association with cankers, and their ability to infect Quercus spp. suggest that they may contribute to the Quercus spp. decline in southwestern Spain.

An Oak Canker Caused by a Gall Midge

An Oak Canker Caused by a Gall Midge

An oak ( Quercus robur L.) canker caused by Stereum rugosum (Pers.) Fr.

A hitherto unreported destructive oak canker in Scotland and its causal organism, Stereum rugosum , have been studied and described from Dawyck, Peebleshire. The cankers, which have been found on trunks of trees about 50–60 years old growing in a damp and shady situation, are mostly open with a depressed to hollow centre which is surrounded by a prominent callus ridge and are often laterally extended. The fructifications of S. rugosum have been found at the edge or near the centre on the surface of the dead bark, usually around the stub of a dead branch. Microscopic characters of the rot are fully described and chemical changes in the wood during the process of decay have been examined. S. rugosum has been obtained in pure culture from areas of both advanced and incipient decay and also from spores. It can be easily identified in culture by its characteristic dense, white, cotton-woolly to felty mycelium, rapid growth and distinctive buff or pinkish buff colour of the mat with age. Inoculations, made on the wounded bark on the trunk of healthy oak tree employing mycelium as the inoculum, were positive. Laboratory studies showed S. rugosum to be able to attack sapwood much more readily than heartwood.