Acute oak decline (AOD) is a disease that infects oak trees originally described in the UK. It mainly affects mature oak trees of over 50 years old of both Britain's native oak species: the pedunculate oak (''

Quercus robur ''Quercus robur'', the pedunculate oak, is a species of flowering plant in the beech and oak family, Fagaceae. It is a large tree, native plant, native to most of Europe and western Asia, and is widely cultivated in other temperate regions. It ...

'') and the sessile oak (''

Quercus petraea ''Quercus petraea'', commonly known as the sessile oak, Welsh oak, Cornish oak, Irish oak or durmast oak, is a species of oak tree native to most of Europe and into Anatolia and Iran. The sessile oak is the national tree of Ireland, and an un ...

''). The disease is characterised by the trees bleeding or oozing a dark fluid from small lesions or splits in their bark. Unlike chronic oak decline, acute oak decline can lead to the death of trees within 4 to 5 years of symptoms appearing. The number of trees affected is thought to number in the low thousands, with a higher number of infected trees being found in the

Midlands The Midlands is the central region of England, to the south of Northern England, to the north of southern England, to the east of Wales, and to the west of the North Sea. The Midlands comprises the ceremonial counties of Derbyshire, Herefor ...

Causes of the disease

Acute Oak Decline is a complex tree decline disease that cannot be explained by a single cause. It results from a combination of environmental factors weakening the trees and some biotic factors.

Bacterial pathogens

Two different species of bacteria, ''Brenneria goodwinii, Gibbsiella quercinecans,'' are repeatedly found in the decaying tissues of trees with AOD. Laboratory experiment confirmed that these two species have the ability to cause tree tissue necrosis and possess virulence genes commonly found in plant pathogens. In addition to these two bacterial pathogens, the other microbes present in AOD affected trees is different from non-infected ones.

Bark-boring beetle

Most trees affected by AOD will display exit holes and galleries caused by the larvae of the two-spotted oak borer '' Agrilus biguttatus'.'' Larvea of ''A. biguttatus'' and the bacterial pathogens are acting together in causing the disease, with the bacteria being more virulent and causing larger lesions when trees are infected with beetle larvae. Researchers are still investing the potential role of ''A. biguttatus'' as a vector of the bacterial pathogens.

Drought and nutrient limitation

As other oak decline disease, AOD usually develops after the tree is being weakened by some environmental factors, called predisposing factors, such as water and nutrient limitation.

Causes of the disease

Bacterial pathogens

Bark-boring beetle

Drought and nutrient limitation

See also

References

Further reading