The foamy bark canker is a disease affecting

oak tree An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably '' ...

s in

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

caused by the

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

''Geosmithia pallida'' and spread by the Western oak

bark beetle 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 ...

('' Pseudopityopthorus pubipennis''). This disease is only seen through the

symbiosis Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

of the bark beetles and the fungal

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

. The bark beetles target oak trees and bore holes through the peridermal tissues, making tunnels within the

phloem Phloem (, ) is the living biological tissue, tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This tran ...

. 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 Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

of the phloem can be observed surrounding the entry hole(s). As the disease progresses, a reddish

sap Sap is a fluid transported in xylem cells (vessel elements or tracheids) or phloem sieve tube elements of a plant. These cells transport water and nutrients throughout the plant. Sap is distinct from latex, resin, or cell sap; it is a separa ...

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 and symptoms

Hosts associated with ''Geosmithia pallida'' include a number of tree species, including oak and other

hardwood Hardwood is wood from dicot trees. These are usually found in broad-leaved temperate and tropical forests. In temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen. Hardwood (which comes from ...

pine A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. The World Flora Online created by the Royal Botanic Gardens, Kew and Missouri Botanical Garden accep ...

and

spruce A spruce is a tree of the genus ''Picea'' (), a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal (taiga) regions of the Earth. ''Picea'' is the sole genus in the subfami ...

trees, depending on the beetle vector.Jankowiak, R. et al. "Association of "Geosmithia" fungi (Ascomycota: Hypocreales) with pine- and spruce-infesting bark beetles in Poland." "

Fungal Ecology The British Mycological Society is a learned society established in 1896 to promote the study of fungi. Formation The British Mycological Society (BMS) was formed by the combined efforts of two local societies: the Woolhope Naturalists' Field ...

" 11 (2014): 71-79. In this case, the western oak bark beetles target

live oak Live oak or evergreen oak is any of a number of oaks in several different sections of the genus ''Quercus'' that share the characteristic of evergreen foliage. These oaks are not more closely related to each other than they are to other oaks. ...

trees of the

western United States The Western United States (also called the American West, the Far West, and the West) is the region comprising the westernmost states of the United States. As American settlement in the U.S. expanded westward, the meaning of the term ''the Wes ...

. 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.Lynch, S.C. et al. ″First Report of "Geosmithia pallida" Causing Foamy Bark Canker, a New Disease on Coast Live Oak ("Quercus agrifolia") in Association with "Pseudopityophthorus pubipennis" in California." "

Plant Disease Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomyc ...

" 98 (2014): 1276-1277. These symptoms, as well as signs (entry holes, larvae, beetles) of bark beetles, are key factors in diagnosis.

Necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...

and

tissues underneath bark can be observed. Common symptoms include: * Wet discoloration on bark * Phloem

* Beetle entry holes * Reddish sap oozing from entry holes * Foamy liquid from entry holes InfectedtreeonStanfordcampus

''Geosmithia putterillii''

''Geosmithia putterillii'', also known as ''Geosmithia pallida'', is a species of

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

of the genus ''

Geosmithia ''Geosmithia'' is a genus of anamorphic fungi of uncertain familial placement in the order Hypocreales. The genus, circumscribed by Australian mycologist John Pitt in 1979, is widely distributed. A 2008 estimate placed ten species in the genus, ...

,'' which was named by Australian mycologist John Pitt in 1979, is widely distributed and contains 10 species.{{cite book , vauthors=Kirk PM, Cannon PF, Minter DW, Stalpers JA , title=Dictionary of the Fungi , edition=10th , publisher=CABI , location=Wallingford, UK , year=2008 , page=281 , isbn=978-0-85199-826-8

Disease cycle

The western bark beetle carries ''G. pallida'' 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 A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

s of ''G. pallida'' are known to function in reproduction of the fungus. Some species of the genus ''

'' are known to produce

apothecia An ascocarp, or ascoma (), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are mo ...

, however it is unclear whether ''G. pallida'' produces this type of spore dispersing structure. The western oak bark beetle is a known vector for transmission of ''G. pallida'' 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.McPherson, Brice A. et al. "Fungal species assemblages associated with ''Phytophthora ramorum''-infected coast live oaks following bark and ambrosia beetle colonization in northern California." "

Forest Ecology and Management ''Forest Ecology and Management'' is a semimonthly peer-reviewed scientific journal covering forest ecology and the management of forest resources. The journal publishes research manuscripts that report results of original research, review articles ...

" 291 (2013): 30-42. 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, ''G. pallida'' 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.

Environment

This disease has been found in the southern coastal regions of

where the climate is mild and constant year-round. A warm,

Mediterranean climate A Mediterranean climate (also called a dry summer temperate climate ''Cs'') is a temperate climate sub-type, generally characterized by warm, dry summers and mild, fairly wet winters; these weather conditions are typically experienced in the ...

is favored by this disease. 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, 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.

Management

Control of the beetle vector is the most effective management technique for disease prevention. Conventional methods of tree

thinning Thinning is a term used in agricultural sciences to mean the removal of some plants, or parts of plants, to make room for the growth of others. Selective removal of parts of a plant such as branches, buds, or roots is typically known as pruning. ...

and the use of

insecticide Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...

s 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. Other cultural techniques of sanitation and overall health of the oak trees by keeping up with watering,

fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...

or mulch needs, and

pruning Pruning is a horticultural, arboricultural, and silvicultural practice involving the selective removal of certain parts of a plant, such as branches, buds, or roots. The practice entails the ''targeted'' removal of diseased, damaged, dead, ...

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.

Importance

Although the disease is caused by a relatively new

, 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 A medical error is a preventable adverse effect of care ("iatrogenesis"), whether or not it is evident or harmful to the patient. This might include an inaccurate or incomplete diagnosis or treatment of a disease, injury, syndrome, behavior, i ...

; it most resembles bacterial wetwood, polyphagous shot hole borer, and

fusarium ''Fusarium'' is a large genus of filamentous fungi, part of a group often referred to as hyphomycetes, widely distributed in soil and associated with plants. Most species are harmless saprobes, and are relatively abundant members of the soil mi ...

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 Wildlife refers to domestication, undomesticated animal species (biology), species, but has come to include all organisms that grow or live wilderness, wild in an area without being species, introduced by humans. Wildlife was also synonymous ...

diversity and for the ecological services they provide like

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

, shelter and food.Ober, Holly K. "The Value of Oaks to Wildlife1." EDIS New Publications RSS.

University of Florida The University of Florida (Florida or UF) is a public land-grant research university in Gainesville, Florida. It is a senior member of the State University System of Florida, traces its origins to 1853, and has operated continuously on its ...

IFAS Extension, n.d. Web. 01 Dec. 2014.

References

External links

Southern California Oaks blog

Geosmithia putterillii
Tree diseases Fungal plant pathogens and diseases Geosmithia