Foamy bark canker | |
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Causal agents | Geosmithia sp.#41 |
Hosts | Oak trees |
Vectors | Western oak bark beetle ( Pseudopityophthorus pubipennis ) |
EPPO Code | GEOHPA |
Distribution | California |
The foamy bark canker is a disease affecting oak trees in California caused by the fungus Geosmithia sp. #41 and spread by the Western oak bark beetle ( Pseudopityophthorus pubipennis ). This disease is only seen through the symbiosis of the bark beetles and the fungal pathogen. The bark beetles target oak trees and bore holes through the peridermal tissues, making tunnels within the phloem. The fungal spores are brought into these tunnels by the beetles and begin to colonize the damaged cells inside the tunnels. Symptoms of the developing fungus include wet discoloration seeping from the beetle entry holes as the fungus begins to consume phloem and likely other tissues. If bark is removed, necrosis of the phloem can be observed surrounding the entry hole(s). As the disease progresses, a reddish sap and foamy liquid oozes from entry holes, thus giving the disease the name foamy bark canker. Eventually, after the disease has progressed, the tree dies. This disease is important because of its detrimental effects on oak trees and its ability to spread to several new Californian counties in just a couple of years.
Hosts associated with Geosmithia sp. #41 include a number of tree species, including oak and other hardwoods, pine and spruce trees, depending on the beetle vector. [1] In this case, the western oak bark beetles target live oak trees of the western United States. Beetles tend to attack stressed trees that are already weakened from drought or injury. Symptoms causing branch dieback and tree death also include a cinnamon-colored gum seeping from multiple beetle entry holes on the bole, followed by a prolific, cream-colored foamy liquid. [2] These symptoms, as well as signs (entry holes, larvae, beetles) of bark beetles, are key factors in diagnosis. Necrosis of xylem and phloem tissues underneath bark can be observed.
Common symptoms include: [3]
Foamy bark canker | |
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Genus: | Geosmithia |
Type species | |
Geosmithia putterillii |
Geosmithia putterillii, also known as Geosmithia pallida, is a species of fungus of the genus Geosmithia, which was named by Australian mycologist John Pitt in 1979, [4] is widely distributed and contains 10 species. [5]
The western bark beetle carries Geosmithia sp. #41 and burrows into the host tree, depositing the fungus inside the phloem where the female beetle lays its eggs. As more beetles are produced, the fungus is picked up and transported to other areas of the host or another host. Conidia spores of Geosmithia sp. #41 are known to function in reproduction of the fungus. [6] Some species of the genus Geosmithia are known to produce apothecia, however it is unclear whether Geosmithia sp. #41 produces this type of spore dispersing structure. The western oak bark beetle is a known vector for transmission of Geosmithia sp. #41 and is responsible for infecting oak tree hosts with fungal inoculum. The beetles may also be responsible for dispersing conidia spores among coast live oak trees. [7] However, it is unclear how the fungus becomes associated with the bark beetles that eventually make their way into the phloem of oak trees. It is possible that spores (or spore-producing structures) are picked up on the soil surface, on woody debris, or on the bark of trees as beetles make their way to oak tree hosts. Spores may attach to the exterior of the beetles, however, this mechanism of association is still unknown. Once the bark beetles have begun tunneling through and consuming phloem tissue, Geosmithia sp. #41 is "dropped" or dispersed throughout the tunnels and is able to begin growth within damaged tissues nearby. The fungus is then able to continue reproduction (by production of conidia), thereby causing disease, once inside the phloem.[ citation needed ]
This disease has been found in the southern coastal regions of California where the climate is mild and constant year-round. A warm, Mediterranean climate is favored by this disease. [8] The pathogen relies on the bark beetle as a vector for dispersal and infection of the host. Bark beetles generally have two or more generations in a single year, [9] leading to disease symptoms in multiple seasons. Because of the multiple generations of bark beetles constantly transporting the fungus, this disease could be considered to be polycyclic if the beetles spread to new hosts.[ citation needed ]
Control of the beetle vector is the most effective management technique for disease prevention. Conventional methods of tree thinning and the use of insecticides have been used to combat the western bark beetles, but are only effective before the beetles have colonized and before the fungus has invaded the tree. [10] Other cultural techniques of sanitation and overall health of the oak trees by keeping up with watering, fertilizer or mulch needs, and pruning may help. It is very important to diagnose foamy bark canker disease correctly and promptly in order to manage the disease properly because if a tree is already infected, the removal of the tree is the most effective way to prevent the disease from spreading.[ citation needed ]
Although the disease is caused by a relatively new symbiosis, it has already spread to a number of different counties, and is completely wiping out oak trees. As mentioned before, this is partially due to disease symptoms that are similar to other diseases leading to a misdiagnosis; it most resembles bacterial wetwood, polyphagous shot hole borer, and fusarium dieback. With the recent outbreak and growth in population of the western bark beetle, there is concern that the pathogen's range will expand. Oak trees are important for wildlife diversity and for the ecological services they provide like habitat, shelter and food. [11]
Pinus elliottii, commonly known as slash pine, is a conifer tree native to the Southeastern United States. Slash pine is named after the "slashes" – swampy ground overgrown with trees and bushes – that constitute its habitat. Other common names include swamp pine, yellow slash pine, and southern Florida pine. Slash pine has two different varieties: P. e. var. elliottii and P. e. var. densa. Historically, slash pine has been an important economic timber for naval stores, turpentine, and resin. The wood of slash pine is known for its unusually high strength, especially for a pine. It exceeds many hardwoods and is even comparable to very dense woods such as ironwood.
Ambrosia beetles are beetles of the weevil subfamilies Scolytinae and Platypodinae, which live in nutritional symbiosis with ambrosia fungi. The beetles excavate tunnels in dead or stressed trees in which they cultivate fungal gardens, their sole source of nutrition. After landing on a suitable tree, an ambrosia beetle excavates a tunnel in which it releases its fungal symbiont. The fungus penetrates the plant's xylem tissue, extracts nutrients from it, and concentrates the nutrients on and near the surface of the beetle gallery. Ambrosia fungi are typically poor wood degraders, and instead utilize less demanding nutrients. Symbiotic fungi produce and detoxify ethanol, which is an attractant for ambrosia beetles and likely prevents growth of antagonistic pathogens and selects for other beneficial symbionts. The majority of ambrosia beetles colonize xylem of recently dead trees, but some attack stressed trees that are still alive, and a few species attack healthy trees. Species differ in their preference for different parts of trees, different stages of deterioration, and in the shape of their tunnels ("galleries"). However, the majority of ambrosia beetles are not specialized to any taxonomic group of hosts, unlike most phytophagous organisms including the closely related bark beetles. One species of ambrosia beetle, Austroplatypus incompertus exhibits eusociality, one of the few organisms outside of Hymenoptera and Isoptera to do so.
A bark beetle is the common name for the subfamily of beetles Scolytinae. Previously, this was considered a distinct family (Scolytidae), but is now understood to be a specialized clade of the "true weevil" family (Curculionidae). Although the term "bark beetle" refers to the fact that many species feed in the inner bark (phloem) layer of trees, the subfamily also has many species with other lifestyles, including some that bore into wood, feed in fruit and seeds, or tunnel into herbaceous plants. Well-known species are members of the type genus Scolytus, namely the European elm bark beetle S. multistriatus and the large elm bark beetle S. scolytus, which like the American elm bark beetle Hylurgopinus rufipes, transmit Dutch elm disease fungi (Ophiostoma). The mountain pine beetle Dendroctonus ponderosae, southern pine beetle Dendroctonus frontalis, and their near relatives are major pests of conifer forests in North America. A similarly aggressive species in Europe is the spruce ips Ips typographus. A tiny bark beetle, the coffee berry borer, Hypothenemus hampei is a major pest on coffee plantations around the world.
A plant canker is a small area of dead tissue, which grows slowly, often over years. Some cankers are of only minor consequence, but others are ultimately lethal and therefore can have major economic implications for agriculture and horticulture. Their causes include a wide range of organisms as fungi, bacteria, mycoplasmas and viruses. The majority of canker-causing organisms are bound to a unique host species or genus, but a few will attack other plants. Weather and animal damage can also cause stress to the plant resulting in cankers. Other causes of cankers is pruning when the bark is wet or using un-sterilized tools.
Ophiostoma ulmi is a species of fungus in the family Ophiostomataceae. It is one of the causative agents of Dutch elm disease. It was first described under the name Graphium ulmi, and later transferred to the genus Ophiostoma.
Alternaria alternata is a fungus causing leaf spots, rots, and blights on many plant parts, and other diseases. It is an opportunistic pathogen on over 380 host species of plant.
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