Bot canker of oak is a disease on stems, branches and twigs of oak trees in Europe and North America. The casual agent of Bot canker of oak is the fungus Botryosphaeria corticola . Bot canker of oak causes lesions and cankers on a wide range of oaks in Europe and most recently live oaks in North America. Some infections were formerly attributed to Botryosphaeria stevensii , but most likely represent infections by Botryosphaeria corticola . Botryosphaeria corticola is distinguishable from Botryosphaeria stevensii via ITS rDNA sequencing.

Overview

Botryosphaeria corticola has caused infection of oak trees in Spain, Portugal, Morocco, Italy, Greece, Hungary, and the United States.
Bot canker of oak kills trees in natural forests as well as in cork

Cork (material)

Cork is an impermeable, buoyant material, a prime-subset of bark tissue that is harvested for commercial use primarily from Quercus suber , which is endemic to southwest Europe and northwest Africa...

 plantations. The cork industry in Portugal, Spain, France, Italy, and Morocco has been dealing with declining oaks for several years from biotic and abiotic factors. This disease has been seen in many cork plantations and is the most important contributor to the decline in the cork industry.
When cork is harvested from the trees, the cork cambium

Cork cambium

Cork cambium is a tissue found in many vascular plants as part of the periderm. The cork cambium is a lateral meristem and is responsible for secondary growth that replaces the epidermis in roots and stems...

 is exposed creating a wound for the fungus to enter the trunk, and cause disease. Infection of other oaks is most likely through wounds, also. These wounds may be natural wounds, but there is evidence insect damage is involved, especially in coast live oak in California. Botryosphaeria corticola infects the twigs, branches and stems of oaks and degrades the cambial

Cambium (botany)

A cambium , in botany, is a tissue layer that provide undifferentiated cells for plant growth. It forms parallel rows of cells, which result in secondary tissues....

 tissues. With the degradation of vascular

Vascular

Vascular in zoology and medicine means "related to blood vessels", which are part of the circulatory system. An organ or tissue that is vascularized is heavily endowed with blood vessels and thus richly supplied with blood....

 tissues the trees display wilting and dieback

Dieback

Dieback may refer to a number of plant problems and diseases including:* Forest dieback caused by acid rain, heavy metal pollution, or imported pathogens* The death of regions of a plant or similar organism caused by physical damage, such as from pruning...

 symptoms.

Hosts

• Europe/North Africa:

Cork oak ( Quercus suber )
Holm oak ( Quercus ilex )
Kermes oak ( Quercus coccifera )
Sessile oak ( Quercus petraea )

• North America:

Canyon live oak ( Quercus chrysolepis )
Coast live oak ( Quercus agrifolia )
Laurel oak ( Quercus laurifolia )
Live oak ( Quercus virginiana )
Grape ( Vitis sp. )

Managment

Botryosphaeria corticola can be managed in high value trees, but there is no current management for forest trees. Carbendazim

Carbendazim

Carbendazim is a widely used broad-spectrum benzimidazole fungicide. A 4.7% solution of carbendazim hydrochloride is sold as Eertavas, an effective treatment for Dutch elm disease....

 and thiophanate-methyl have shown to prevent infection in cork oak in Europe, where it is applied after cork has been harvested. Sanitation is the most common management technique for this disease. Branches with diseased tissue are pruned off, and heavily infected trees are removed. This prevents future infections by limiting the amount of spores in the area.

Description

Botryosphaeria corticola ( Diplodia corticola ) is a ascomycete fungus. It has both sexual ( Diplodia corticola ) and asexual ( Botryosphaeria corticola ) stages occurring naturally.
The asexual spores

Spore

In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...

 (conidia) occur in pycnidia

Pycnidium

A pycnidium is an asexual fruiting body produced by mitosporic fungi in the form order Sphaeropsidales . It is often spherical or inversely pearshaped and its internal cavity is lined with conidiophores. When ripe, an opening generally appears at the top, through which the pycnidiospores escape....

 from conidiogenous cells, without conidiophores

Conidium

Conidia, sometimes termed conidiospores, are asexual, non-motile spores of a fungus and are named after the greek word for dust, konia. They are also called mitospores due to the way they are generated through the cellular process of mitosis...

. Pycnidia are dark brown to black, circular, immersed, partially erumpent and up to 1 mm diameter.
The sexual spores are eight biseriate

Biseriate

A botanical term applied to both the Kingdom plantae, and fungi, meaning 'arranged in two rows'.This can refer to any number of structures within these kingdoms, from arrangement of leaves, to the placement of spores....

 ascospores

Ascospore

An ascospore is a spore contained in an ascus or that was produced inside an ascus. This kind of spore is specific to fungi classified as ascomycetes ....

 occur inside of asci occur in immersed, partially erumpent, dark brown to black pseudothecia

Dothideomycetes

Dothideomycetes is the largest and most diverse class of ascomycete fungi. It comprises 11 orders 90 families, 1300 genera and over 19,000 known species. Traditionally, most of its members were included in the loculoascomycetes, which is not part of the currently accepted classification...

, up to 1 mm in diameter.