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''Phytophthora cinnamomi'', also known as cinnamon fungus, is a soil-borne
water mould The Oomycetes (), or Oomycota, form a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms within the Stramenopiles. They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction o ...
that produces an infection which causes a condition in plants variously called "dieback", "
root rot Root rot is a condition in which anoxic conditions in the soil or potting media around the roots of a plant cause them to rot. This occurs due to excessive standing water around the roots.-Hydroponics Root Rot: What is It, How To Treat It, How ...
", or (in certain ''
Castanea The chestnuts are the deciduous trees and shrubs in the genus ''Castanea'', in the beech family Fagaceae. The name also refers to the edible nuts they produce. They are native to temperate regions of the Northern Hemisphere. Description C ...
'' species), "ink disease". Once infected soil or water is introduced, the organism can spread rapidly throughout an environment. An infestation can lead to the illness, death, and possible eradication of vulnerable plants, as well as habitat reduction for animals. An outbreak can be challenging to recognize and can inflict irreversible harm to ecosystems. The plant pathogen is one of the world's most
invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...
and is present in over 70 countries around the world.


Distribution and hosts

''Phytophythora cinnamomi'' is distributed worldwide and can infect a diverse range of hosts, including
club moss Lycopodiopsida is a class of vascular plants also known as lycopsids, lycopods, or lycophytes. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching stems bearing simple leaves ...
es,
fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...
s,
cycad Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants o ...
s,
conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...
s, cord rushes,
grass Poaceae ( ), also called Gramineae ( ), is a large and nearly ubiquitous family (biology), family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos, the grasses of natural grassland and spe ...
es,
lilies ''Lilium'' ( ) is a genus of herbaceous flowering plants growing from bulbs, all with large and often prominent flowers. Lilies are a group of flowering plants which are important in culture and literature in much of the world. Most species are ...
and a large number of species from many dicotyledonous families, and is included in the
Invasive Species Specialist Group Invasive may refer to: *Invasive (medical) procedure *Invasive species *Invasive observation, especially in reference to surveillance *Invasively progressive spread of disease from one organ in the body to another, especially in reference to cancer ...
list of "100 of the World's Worst Invasive Alien Species". Its potential range is expected to extend polewards with warming due to
climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
. It affects a range of economic plants, including food crops such as
avocado The avocado, alligator pear or avocado pear (''Persea americana'') is an evergreen tree in the laurel family (Lauraceae). It is native to Americas, the Americas and was first domesticated in Mesoamerica more than 5,000 years ago. It was priz ...
and
pineapple The pineapple (''Ananas comosus'') is a Tropical vegetation, tropical plant with an edible fruit; it is the most economically significant plant in the family Bromeliaceae. The pineapple is indigenous to South America, where it has been culti ...
; as well as trees and woody ornamentals such as
Fraser fir The Fraser fir (''Abies fraseri''), sometimes spelled Frasier fir, is an endangered species of fir native to the Appalachian Mountains of the southeastern United States. They are endemic to only seven montane regions in the Appalachian Mountains ...
s,
shortleaf pine The shortleaf pine or ''Pinus echinata'' is a species of coniferous tree endemic to the United States. The shortleaf pine is sometimes referred to as the "old field", "spruce", "rosemary", "yellow", "two-leaf" and "heart" pine. The common name " ...
s,
loblolly pine ''Pinus taeda'', commonly known as loblolly pine, is one of several pines native to the Southeastern United States, from East Texas to Florida, and north to southern New Jersey. The wood industry classifies the species as a southern yellow pi ...
s,
azalea Azaleas ( ) are flowering shrubs in the genus ''Rhododendron'', particularly the former sections ''Rhododendron sect. Tsutsusi, Tsutsusi'' (evergreen) and ''Pentanthera'' (deciduous). Azaleas bloom in the spring (April and May in the temperate ...
s,
camellia ''Camellia'' (pronounced or ) is a genus of flowering plants in the family Theaceae. They are found in tropical and subtropical areas in East Asia, eastern and South Asia, southern Asia, from the Himalayas east to Japan and Indonesia. There are ...
and
boxwood ''Buxus'' is a genus of about seventy species in the family Buxaceae. Common names include box and boxwood. The boxes are native to western and southern Europe, southwest, southern and eastern Asia, Africa, Madagascar, northernmost So ...
, causing root rot, dieback and death of infected plants. Symptoms include wilting, decreased fruit size and yield, collar rot, gum exudation, necrosis, leaf chlorosis, leaf curl, and stem cankers. It can also cause dieback of young shoots and may interfere with transpiration of roots to shoots. Older plants may not display symptoms or only exhibit mild dieback despite having severe root rot.


Reproduction

''Phytophthora cinnamomi'' is a
diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...
and primarily
heterothallic Heterothallic species have sexes that reside in different individuals. The term is applied particularly to distinguish heterothallic fungi, which require two compatible partners to produce sexual spores, from homothallic ones, which are capable ...
species with two mating types, A1 and A2. Sexual reproduction in heterothallic ''Phytophthora'' species ordinarily occurs when
gametangia A gametangium (: gametangia) is a sex organ or cell in which gametes are produced that is found in many multicellular protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists ...
of opposite mating type interact in host tissue. This interaction leads to the formation of
oospore An oospore is a thick-walled sexual spore that develops from a fertilized oosphere in some algae, fungi, and oomycetes. They are believed to have evolved either through the fusion of two species or the chemically induced stimulation of mycelia ...
s that can survive for long periods in or outside the host. ''Phytophthora cinnamomi'' is facultatively
homothallic In fungi and algae, homothallism refers to the condition in which a single individual or thallus carries the genetic determinants (i.e., both mating types or sexes) required to undergo sexual reproduction without the need for a distinct mating partn ...
and capable of self-fertilization. Cultures of mating type A2 can be induced to undergo sexual reproduction by damaging conditions such as exposure to hydrogen peroxide or mechanical damage.


Life cycle

''Phytophthora cinnamomi'' lives in the soil and in plant tissues and can spread in water. During periods of harsh environmental conditions, the organisms become dormant
chlamydospore A chlamydospore is the thick-walled large resting spore of several kinds of fungi, including Ascomycota such as '' Candida'', Basidiomycota such as '' Panus'', and various Mortierellales species. It is the life-stage which survives in unfavourab ...
s. When environmental conditions are suitable, the chlamydospores germinate, producing
mycelia Mycelium (: mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Its normal form is that of branched, slender, entangled, anastomosing, hyaline threads. Fungal colonies composed of mycelium are fo ...
(or hyphae) and
sporangia A sporangium (from Late Latin, ; : sporangia) is an enclosure in which spores are formed. It can be composed of a unicellular organism, single cell or can be multicellular organism, multicellular. Virtually all plants, fungus, fungi, and many ot ...
. The sporangia ripen and release
zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion in aqueous or moist environments. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Certain zoospores are ...
s, which infect plant
root In vascular plants, the roots are the plant organ, organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often bel ...
s by entering the root behind the root tip. Zoospores need water to move through the soil, therefore infection is most likely in moist soils. After entering the root, mycelia grow throughout the root absorbing
carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...
s and nutrients and destroy the structure of the root tissues, "rotting" the root and preventing the plant from absorbing water and nutrients. Sporangia and chlamydospores form on the mycelia of the infected root allowing further dispersal.


Transmission

Although ''P. cinnamomi'' was first identified in tropical and subtropical countries, but can survive and develop in cooler climates as well. It spreads as zoospores and/or chlamydospores in soil and water under favourable conditions such as warm temperatures and high soil moisture. Methods of transmission include local invasion via contact between the roots of infected and susceptible plants, downslope movement in surface or subsurface water such as rivers or irrigation water, zoospore dispersal over long distances via wind-blown soil and debris, and transport of infected plant matter and soil, for example via particles stuck to footwear, vehicles or equipment. Native and feral animals have been known to transport the disease, including through the digestive tract of feral pigs. However human activities such as timber harvesting, mining, bush walking, and road construction are also major methods of dispersal.


Environmental impacts

When ''Phytophthora'' dieback spreads to native plant communities, it kills many susceptible plants, resulting in a permanent decline in the biodiversity and a disruption of ecosystem processes. It can also change the composition of the forest or native plant community by increasing the number of resistant plants and reducing the number of susceptible plant species. Native animals that rely on susceptible plants for survival are reduced in numbers or are eliminated from sites infested by ''Phytophthora'' dieback.


Australia

In
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
, where it is known as phytophthora dieback, dieback, jarrah dieback or cinnamon fungus, ''Phytophthora cinnamomi'' can infect thousands of native plants, causing damage to forests and removing habitats for wildlife. Several native plants are at risk of extinction due to the effects of the disease. ''Phytophthora cinnamomi''s impact is greatest in
Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...
,
Victoria Victoria most commonly refers to: * Queen Victoria (1819–1901), Queen of the United Kingdom and Empress of India * Victoria (state), a state of Australia * Victoria, British Columbia, Canada, a provincial capital * Victoria, Seychelles, the capi ...
,
Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...
and
South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...
, while the
Northern Territory The Northern Territory (abbreviated as NT; known formally as the Northern Territory of Australia and informally as the Territory) is an states and territories of Australia, Australian internal territory in the central and central-northern regi ...
remains unaffected due to the unfavourability of the environment. Of particular concern is the infection and dieback of large areas of forest and heathland which support
threatened species A threatened species is any species (including animals, plants and fungi) which is vulnerable to extinction in the near future. Species that are threatened are sometimes characterised by the population dynamics measure of ''critical depensatio ...
in the south-west
Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...
. Many plants from the genera ''
Banksia ''Banksia'' is a genus of around 170 species of flowering plants in the family Proteaceae. These Australian wildflowers and popular garden plants are easily recognised by their characteristic flower spikes, and woody fruiting "cones" and head ...
'', ''
Darwinia Darwinia may refer to: * ''Darwinia'' (plant) Rudge 1815, a genus of Myrtaceae found only in Australia *''Darwinia'' Raf., a synonym of the legume genus '' Sesbania'' Adans. * ''Darwinia'' (video game), a 2005 video game by Introversion Software * ' ...
'', ''
Grevillea ''Grevillea'' (), commonly known as spider flowers, is a genus of about 360 species of evergreen flowering plants in the family Proteaceae. Plants in the genus ''Grevillea'' are shrubs, rarely trees, with the leaves arranged alternately along the ...
'', ''
Leucopogon ''Leucopogon'' is a genus of about 150-160 species of shrubs or small trees in the family Ericaceae, in the section of that family formerly treated as the separate family Epacridaceae. They are native to Australia, New Zealand, New Caledonia, the ...
'', ''
Verticordia :For the clam genus, see ''Verticordia'' (bivalve). ''Verticordia'' is a genus of more than 100 species of plants commonly known as featherflowers, in the myrtle family, Myrtaceae. They range in form from very small shrubs such as '' V. verticor ...
'' and ''
Xanthorrhoea ''Xanthorrhoea'' () is a genus of about 30 species of Succulent plant, succulent flowering plants in the family Asphodelaceae. They are Endemism, endemic to Australia. Common names for the plants include grasstree, grass gum-tree (for resin-yie ...
'' are susceptible. This in turn impacts on animals reliant on these plants for food and shelter, such as the
southwestern pygmy possum The western pygmy possum (''Cercartetus concinnus''), also known as the southwestern pygmy possum or the ''mundarda'', is a small marsupial found in Australia. Genetic studies indicate its closest relative is probably the eastern pygmy possum, f ...
(''Cercartetus concinnus'') and the
honey possum The honey possum or noolbenger (''Tarsipes rostratus''), is a tiny species of marsupial that feeds on the nectar and pollen of a diverse range of flowering plants. Found only in southwest Australia, it is an important pollinator for such plants ...
(''Tarsipes rostratus''). A study in the Perth region found that dieback caused a significant shift in the bird community and affected nectar-feeding species the most, with fewer species such as the
Western Spinebill The western spinebill (''Acanthorhynchus superciliosus'') is a honeyeater found in the Heath (habitat), heath and woodland of Southwest Australia, south-western Australia. Ranging between long, it weighs around . It has a black head, gray back a ...
in areas that were dieback-infested.


New Zealand

In
New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
, ''Phytophthora cinnamomi'' (or a local variant ''Phytophthora agathidicida''?) appeared in recent years and has now been recognized as a major pathogen of the endemic Kauri Tree ''
Agathis australis ''Agathis australis'', commonly known as kauri, is a species of coniferous tree in the family Araucariaceae, found north of 38°S in the northern regions of New Zealand's North Island. It is the largest (by volume) but not tallest species ...
'', causing Kauri dieback disease.


U.S. and Mexico

Damage to forests suspected to be caused by ''Phytophthora cinnamomi'' was first recorded in the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
about 200 years ago. Infection can cause littleleaf disease of
shortleaf pine The shortleaf pine or ''Pinus echinata'' is a species of coniferous tree endemic to the United States. The shortleaf pine is sometimes referred to as the "old field", "spruce", "rosemary", "yellow", "two-leaf" and "heart" pine. The common name " ...
(''Pinus echinata''), Christmas tree disease in nursery grown
Fraser fir The Fraser fir (''Abies fraseri''), sometimes spelled Frasier fir, is an endangered species of fir native to the Appalachian Mountains of the southeastern United States. They are endemic to only seven montane regions in the Appalachian Mountains ...
(''Abies fraseri''), and sudden death of a number of native tree species such as
American chestnut The American chestnut (''Castanea dentata'') is a large, fast-growing deciduous tree of the Fagaceae, beech family native to eastern North America. As is true of all species in the genus ''Chestnut, Castanea'', the American chestnut produces Bur ...
.
Oak An oak is a hardwood tree or shrub in the genus ''Quercus'' of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisp ...
populations are affected in areas ranging from
South Carolina South Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders North Carolina to the north and northeast, the Atlantic Ocean to the southeast, and Georgia (U.S. state), Georg ...
to
Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...
. ''Phytophthora cinnamomi'' is also a problem in the
Mexican state A Mexican State (), officially the Free and Sovereign State (), is a constituent federative entity of Mexico according to the Constitution of Mexico. Currently there are 31 states, each with its own constitution, government, state governor, a ...
of
Colima Colima, officially the Free and Sovereign State of Colima, is among the 31 states that make up the 32 Federal Entities of Mexico. It shares its name with its capital and main city, Colima. Colima is a small state of western Mexico on the cen ...
, killing several native oak species and other susceptible vegetation in the surrounding woodlands. It is implicated in the die-off of the rare endemic shrub Ione manzanita (''Arctostaphylos myrtifolia'') in
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
.


Commercial effects

''Phytophthora cinnamomi'' is the leading cause of damage to
avocado The avocado, alligator pear or avocado pear (''Persea americana'') is an evergreen tree in the laurel family (Lauraceae). It is native to Americas, the Americas and was first domesticated in Mesoamerica more than 5,000 years ago. It was priz ...
trees, and is commonly known as "root rot" amongst avocado farmers. Since the 1940s various breeds of root rot-resistant avocados have been developed to minimize tree damage. Damaged trees generally die or become unproductive within three to five years. A 1960 study of the
Fallbrook, California Fallbrook is a census-designated place in northern San Diego County, California. It had a population of 32,267 at the 2020 census. Fallbrook is immediately east of the U.S. Marine Corps' Camp Pendleton. It is known for its avocado groves and c ...
, area correlated higher levels of avocado root rot to soils with poorer drainage and greater
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
content.


Control

No treatment has been found to eradicate ''P. cinnamomi'', although an integrated approach can control the spread and impact of the disease. Gardening practices to restrict spread include restricting soil or water movement from infected areas by using clean bins and equipment, installing watertight drains to prevent surface run off, and working last in diseased areas after harvesting healthy areas first. Planting in raised beds promotes rapid drainage and reduces prolonged contact of plant roots with water, making the soil environment less hospitable to ''P. cinnamomi''. For specific plants such as young avocado plants, soil solarisation by using clear polythene sheets laid on the soil surface to trap radiant heat from the sun can reduce spread, and an integrated approach is generally taken to control disease on avocado. Chemical means of control include fumigation and the use of phosphonate fungistats. Fumigation prior to planting may be effective on some life stages of ''P. cinnamomi'', but does not eliminate chlamydospores as they are present deeper in the soil where fumigation may not reach. However, fumigation can potentially worsen disease by reducing the population of competing soil microorganisms, and ''P. cinnamomi'' is often able to re-invade fumigated soil. Phosphonate fungistats can improve the ability of a tree to tolerate, resist, or recover from infection.
Phosphite The general structure of a phosphite ester showing the lone pairs on the P In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of ...
administered through direct foliage sprays, aerial application by aircraft or direct injection has been used to limit the disease with some success and has been recognized as a major strategy for disease prevention. Commonly potassium phosphite is used as a biodegradable fungicide, and calcium or magnesium phosphite may also be used. Overuse of phosphite may harm the treated plant, especially when the plant is phosphate deficient.


See also

*
Chlorosis In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...
*
Forest pathology Forest pathology is the research of both biotic and abiotic maladies affecting the health of a forest ecosystem, primarily fungal pathogens and their insect vectors. It is a subfield of forestry and plant pathology. Forest pathology is part ...


References


External links

* * * * * * * * *
fact sheet of the Global Invasive Species database
* * {{Authority control cinnamomi Water mould plant pathogens and diseases Avocado tree diseases