''Phytophthora'' (from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

(''phytón''), "plant" and (), "destruction"; "the plant-destroyer") is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial no ...

of plant-damaging

oomycete Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the r ...

s (water molds), whose member species are capable of causing enormous economic losses on crops worldwide, as well as

environmental damage Environmental degradation is the deterioration of the environment through depletion of resources such as quality of air, water and soil; the destruction of ecosystems; habitat destruction; the extinction of wildlife; and pollution. It is d ...

in natural

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

s. As well as impacting large scale agriculture, ''Phytophthora'' is a nuisance to garden and indoor plant hobbyists as well as bonsai artists. The cell wall of ''Phytophthora'' is made up of cellulose. The genus was first described by Heinrich Anton de Bary in 1875. Approximately 170 species have been described, although 100–500 undiscovered ''Phytophthora'' species are estimated to exist.

Pathogenicity

''Phytophthora'' spp. are mostly pathogens of

dicotyledon The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, ...

s, and many are relatively host-specific parasites. '' Phytophthora cinnamomi'', though, infects thousands of species ranging from club mosses,

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...

cycad Cycads are seed plants that typically have a stout and woody ( ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male o ...

conifer Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All ex ...

grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns ...

es,

lilies ''Lilium'' () is a genus of herbaceous flowering plants growing from bulbs, all with large prominent flowers. They are the true lilies. Lilies are a group of flowering plants which are important in culture and literature in much of the world. ...

, to members of many dicotyledonous families. Many species of ''Phytophthora'' are

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae ex ...

pathogen In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process ...

s of considerable economic importance. '' Phytophthora infestans'' was the infective agent of the potato blight that caused the Great Famine of Ireland, and still remains the most destructive pathogen of solanaceous crops, including tomato and potato. The soya bean root and stem rot agent, '' Phytophthora sojae'', has also caused longstanding problems for the agricultural industry. In general, plant diseases caused by this genus are difficult to control chemically, thus the growth of resistant

cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...

s is the main management strategy. Other important ''Phytophthora'' diseases are: * '' Phytophthora agathidicida''—causes collar-rot on

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island country ...

kauri (''

Agathis australis ''Agathis australis'', commonly known by its Māori name kauri (), is a 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 ...

''), New Zealand's most voluminous tree, an otherwise successful survivor of the

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

* '' Phytophthora cactorum''—causes rhododendron root rot affecting rhododendrons, azaleas, and

orchids Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Along with the Asteraceae, they are one of the two largest families of flowering ...

, and causes bleeding canker in hardwood trees * '' Phytophthora capsici''—infects

Cucurbitaceae The Cucurbitaceae, also called cucurbits or the gourd family, are a plant family consisting of about 965 species in around 95 genera, of which the most important to humans are: *'' Cucurbita'' – squash, pumpkin, zucchini, some gourds *'' La ...

fruits, such as

cucumber Cucumber (''Cucumis sativus'') is a widely-cultivated creeping vine plant in the Cucurbitaceae family that bears usually cylindrical fruits, which are used as culinary vegetables.squash * '' Phytophthora cinnamomi''—causes cinnamon root rot affecting forest and fruit trees, and woody ornamentals including arborvitaee,

azalea Azaleas are flowering shrubs in the genus ''Rhododendron'', particularly the former sections '' Tsutsusi'' (evergreen) and '' Pentanthera'' (deciduous). Azaleas bloom in the spring (April and May in the temperate Northern Hemisphere, and Octo ...

Chamaecyparis ''Chamaecyparis'', common names cypress or false cypress (to distinguish it from related cypresses), is a genus of conifers in the cypress family Cupressaceae, native to eastern Asia ( Japan and Taiwan) and to the western and eastern margins of ...

dogwood ''Cornus'' is a genus of about 30–60 species of woody plants in the family Cornaceae, commonly known as dogwoods, which can generally be distinguished by their blossoms, berries, and distinctive bark. Most are deciduous trees or shrub ...

forsythia ''Forsythia'' , is a genus of flowering plants in the olive family Oleaceae. There are about 11 species, mostly native to eastern Asia, but one native to southeastern Europe. ''Forsythia'' – also one of the plant's common names – i ...

Fraser fir The Fraser fir (''Abies fraseri'') is a species of fir native to the Appalachian Mountains of the Southeastern United States. ''Abies fraseri'' is closely related to ''Abies balsamea'' (balsam fir), of which it has occasionally been treated ...

, hemlock, Japanese holly,

juniper Junipers are coniferous trees and shrubs in the genus ''Juniperus'' () of the cypress family Cupressaceae. Depending on the taxonomy, between 50 and 67 species of junipers are widely distributed throughout the Northern Hemisphere, from the Arc ...

, Pieris,

rhododendron ''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species of woody plants in the heath family (Ericaceae). They can be either evergreen or deciduous. Most species are nati ...

Taxus ''Taxus'' is a genus of coniferous trees or shrubs known as yews in the family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of , with trunk girth averaging . They have reddish bark, lanceolate, flat, ...

white pine ''Pinus'', the pines, is a genus of approximately 111 extant tree and shrub species. The genus is currently split into two subgenera: subgenus ''Pinus'' (hard pines), and subgenus ''Strobus'' (soft pines). Each of the subgenera have been further ...

American chestnut The American chestnut (''Castanea dentata'') is a large, fast-growing deciduous tree of the beech family native to eastern North America. As is true of all species in genus Castanea, the American chestnut produces burred fruit with edible nuts ...

and Australian woody plants, especially eucalypt and banksia. * '' Phytophthora citricola''—causes root rot and stem cankers in citrus trees * '' Phytophthora fragariae''—causes red root rot affecting strawberries * '' Phytophthora infestans'' causes the serious disease known as potato (late) blight: responsible for the Great Famine of Ireland. * '' Phytophthora kernoviae''—pathogen of

beech Beech (''Fagus'') is a genus of deciduous trees in the family Fagaceae, native to temperate Europe, Asia, and North America. Recent classifications recognize 10 to 13 species in two distinct subgenera, ''Engleriana'' and ''Fagus''. The ''Engle ...

and rhododendron, also occurring on other trees and shrubs including

oak 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 ...

, and holm oak. First seen in Cornwall, UK, in 2003. * ''

Phytophthora lateralis ''Phytophthora lateralis'' is a soil-borne plant pathogen that causes cedar root disease in Lawson cypresses (''Chamaecyparis lawsoniana'') in Northern USA. This pathogen was first noted to cause disease in around 1920 on nursery stock near Sea ...

''—causes cedar root disease in Port Orford cedar trees * '' Phytophthora megakarya''—one of the cocoa black pod disease species, is invasive and probably responsible for the greatest cocoa crop loss in Africa * '' Phytophthora multivora''—discovered in analysis of isolates with ''P. cinnamomi'' dieback infections of tuart forests of Southwest Australia, which were previously diagnosed as ''P. citricola''. The species was found occurring on many other taxa, so named ''multivora''. * '' Phytophthora nicotianae''—infects

onion An onion (''Allium cepa'' L., from Latin ''cepa'' meaning "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus ''Allium''. The shallot is a botanical variety of the oni ...

s * '' Phytophthora palmivora''—causes fruit rot in

coconut The coconut tree (''Cocos nucifera'') is a member of the palm tree family ( Arecaceae) and the only living species of the genus ''Cocos''. The term "coconut" (or the archaic "cocoanut") can refer to the whole coconut palm, the seed, or th ...

s and

betel nut The betel (''Piper betle'') is a vine of the family Piperaceae, which includes pepper and kava. The betel plant is native to Southeast Asia. It is an evergreen, dioecious perennial, with glossy heart-shaped leaves and white catkins. Betel plan ...

s * '' Phytophthora ramorum''—infects over 60 plant genera and over 100 host species; causes sudden oak death * '' Phytophthora quercina''—causes oak death * '' Phytophthora sojae''—causes

soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu ...

root rot Research beginning in the 1990s has placed some of the responsibility for European forest die-back on the activity of imported Asian ''Phytophthoras''. In 2019, scientists in Connecticut were conducting experiments testing various methods to grow healthier Fraser trees when they accidentally discovered a new species of ''Phytophthora'', which they called ''Phytophthora abietivora''. The fact that these scientists so readily discovered a new species further suggests that there could be many more species waiting to be discovered.

Species

Resemblance to fungi

''Phytophthora'' is sometimes referred to as a

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 ...

-like organism, but it is classified under a different

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

altogether:

SAR supergroup The SAR supergroup, also just SAR or Harosa, is a clade that includes stramenopiles (heterokonts), alveolates, and Rhizaria. The name is an acronym derived from the first letters of each of these clades; it has been alternatively spelled "RAS". ...

(Harosa) (also under Stramenopila and previously under Chromista). This is a good example of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

: ''Phytophthora'' is morphologically very similar to true fungi yet its evolutionary history is completely distinct. In contrast to fungi, SAR supergroup is more closely related to plants than to animals. Whereas fungal cell walls are made primarily of

chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...

, ''Phytophthora'' cell walls are constructed mostly of

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell w ...

. Ploidy levels are different between these two groups; ''Phytophthora'' species have

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. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectiv ...

(paired) chromosomes in the vegetative (growing, nonreproductive) stage of life, whereas fungi are almost always

haploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respecti ...

in this stage. Biochemical pathways also differ, notably the highly conserved

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated − ...

synthesis path.

Biology

''Phytophthora'' species may reproduce sexually or asexually. In many species, sexual structures have never been observed, or have only been observed in laboratory matings. In homothallic species, sexual structures occur in single culture.

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 have mating strains, designated as A1 and A2. When mated, antheridia introduce gametes into

oogonia An oogonium (plural oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes. In the mammalian fetus Oogonia are formed in larg ...

, either by the oogonium passing through the antheridium (amphigyny) or by the antheridium attaching to the proximal (lower) half of the oogonium (paragyny), and the union producing oospores. Like animals, but not like most true fungi, meiosis is gametic, and somatic nuclei are diploid. Asexual (mitotic) spore types are chlamydospores, and

sporangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their lif ...

which produce

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or mo ...

s. Chlamydospores are usually spherical and pigmented, and may have a thickened cell wall to aid in their role as a survival structure. Sporangia may be retained by the subtending hyphae (noncaducous) or be shed readily by wind or water tension (caducous) acting as dispersal structures. Also, sporangia may release zoospores, which have two unlike

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...

which they use to swim towards a host plant. Zoospores (and zoospores of ''

Pythium ''Pythium'' is a genus of parasitic oomycetes. They were formerly classified as fungi. Most species are plant parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet of the fungus gnat are frequ ...

'', also in the Peronosporales) recognize not only hosts but particular locations on hosts. ''Phytophthora'' zoospores recognize and attach to specific root surface regions. This is a high degree of specificity at an early stage of cell development.

References

External links

* [https://web.archive.org/web/20070506074931/http://www.ladybug.uconn.edu/factsheets/tp_05_phytophthora.html Abbey, Tim (2005) "Phytophthora Dieback and Root Rot" College of Agriculture and Natural Resources, University of Connecticut]
"''Phytophthora'' Canker – Identification, Biology and Management"
Bartlett Tree Experts Online Resource Library
"''Phytophthora'' Root Rot – Identification, Biology and Management"
Bartlett Tree Experts Online Resource Library
Dieback Working Group
– Western Australia {{Taxonbar, from=Q311294 Water mould plant pathogens and diseases Water mould genera