Phytophthora

Phytophthora (from Greek (phytón), "plant" and , "destruction"; "the plant-destroyer") is a genus of plant-damaging oomycetes (water molds), whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems. The cell wall of Phytophthora is made up of cellulose. The genus was first described by Heinrich Anton de Bary in 1875. Approximately 210 species have been described, although 100–500 undiscovered Phytophthora species are estimated to exist.
Pathogenicity
Phytophthora spp. are mostly pathogens of dicotyledons, and many are relatively host-specific parasites. Phytophthora cinnamomi, though, infects thousands of species ranging from club mosses, ferns, cycads, conifers, grasses, lilies, to members of many dicotyledonous families. Many species of Phytophthora are plant pathogens 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 cultivars is the main management strategy.
Other important Phytophthora diseases are:
Phytophthora agathidicida—causes collar-rot on New Zealand kauri (Agathis australis), New Zealand's most voluminous tree, an otherwise successful survivor of the Jurassic
Phytophthora cactorum—causes rhododendron root rot affecting rhododendrons, azaleas, and orchids, and causes bleeding canker in hardwood trees
Phytophthora capsici—infects Cucurbitaceae fruits, such as cucumbers and squash
Phytophthora cinnamomi—causes cinnamon root rot affecting forest and fruit trees, and woody ornamentals including arborvitaee, azalea, Chamaecyparis, dogwood, forsythia, Fraser fir, hemlock, Japanese holly, juniper, Pieris, rhododendron, Taxus, white pine, American chestnut 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 and rhododendron, also occurring on other trees and shrubs including oak, and holm oak. First seen in Cornwall, UK, in 2003.
Phytophthora lateralis—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 tobacco and onions
Phytophthora palmivora—causes fruit rot in coconuts and betel nuts
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 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.
Reproduction
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 species have mating strains, designated as A1 and A2. When mated, antheridia introduce gametes into oogonia, 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 which produce zoospores. 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 which they use to swim towards a host plant.
Zoospores (and zoospores of Pythium, 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.
Evolution and resemblance to fungi
Phytophthora is sometimes referred to as a fungus-like organism, but it is classified under a different clade altogether: SAR supergroup (Harosa) (also under Stramenopila and previously under Chromista). This is a good example of convergent evolution: 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, Phytophthora cell walls are constructed mostly of cellulose. Ploidy levels are different between these two groups; Phytophthora species have diploid (paired) chromosomes in the vegetative (growing, nonreproductive) stage of life, whereas fungi are almost always haploid in this stage. Biochemical pathways also differ, notably the highly conserved lysine synthesis path.
Species
The NCBI lists:
Phytophthora acerina
Phytophthora afrocarpa
Phytophthora agathidicida
Phytophthora aleatoria
Phytophthora alni
Phytophthora × alni
Phytophthora alpina
Phytophthora alticola
Phytophthora amaranthi
Phytophthora amnicola
Phytophthora amnicola × moyootj
Phytophthora xandina
Phytophthora aquimorbida
Phytophthora arecae
Phytophthora arenaria
Phytophthora cf. arenaria
Phytophthora aff. arenaria
Phytophthora asiatica
Phytophthora asparagi
Phytophthora aff. asparagi
Phytophthora attenuata
Phytophthora austrocedrae
Phytophthora balyanboodja
Phytophthora batemanensis syn. Halophytophthora batemanensis
Phytophthora betacei
Phytophthora bilorbang
Phytophthora bishii
Phytophthora boehmeriae
Phytophthora boodjera
Phytophthora borealis
Phytophthora botryosa
Phytophthora cf. botryosa
Phytophthora aff. botryosa
Phytophthora brassicae
Phytophthora cactorum
Phytophthora cactorum var. applanata
Phytophthora cactorum × hedraiandra
Phytophthora cajani
Phytophthora × cambivora
Phytophthora capensis
Phytophthora capsici
Phytophthora aff. capsici
Phytophthora captiosa
Phytophthora castaneae
Phytophthora castanetorum
Phytophthora chesapeakensis
Phytophthora chlamydospora
Phytophthora chrysanthemi
Phytophthora cichorii
Phytophthora aff. cichorii
Phytophthora cinnamomi
Phytophthora cinnamomi var. cinnamomi
Phytophthora cinnamomi var. parvispora
Phytophthora cinnamomi var. robiniae
Phytophthora citricola
Phytophthora aff. citricola
Phytophthora citrophthora
Phytophthora citrophthora var. clementina
Phytophthora aff. citrophthora
Phytophthora clandestina
Phytophthora cocois
Phytophthora colocasiae
Phytophthora condilina
Phytophthora constricta
Phytophthora cooljarloo
Phytophthora crassamura
Phytophthora cryptogea
Phytophthora aff. cryptogea
Phytophthora cuyabensis
Phytophthora cyperi
Phytophthora dauci
Phytophthora aff. dauci
Phytophthora drechsleri
Phytophthora drechsleri var. cajani
Phytophthora elongata
Phytophthora cf. elongata
Phytophthora erythroseptica
Phytophthora erythroseptica var. pisi
Phytophthora aff. erythroseptica
Phytophthora estuarina
Phytophthora europaea
Phytophthora fallax
Phytophthora flexuosa
Phytophthora fluvialis
Phytophthora fluvialis × moyootj
Phytophthora foliorum
Phytophthora formosa
Phytophthora formosana
Phytophthora fragariae
Phytophthora fragariaefolia
Phytophthora frigida
Phytophthora gallica
Phytophthora gemini
Phytophthora gibbosa
Phytophthora glovera
Phytophthora gonapodyides
Phytophthora gondwanensis
Phytophthora gregata
Phytophthora cf. gregata
Phytophthora hedraiandra
Phytophthora aff. hedraiandra
Phytophthora × heterohybrida
Phytophthora heveae
Phytophthora hibernalis
Phytophthora himalayensis
Phytophthora himalsilva
Phytophthora aff. himalsilva
Phytophthora humicola
Phytophthora aff. humicola
Phytophthora hydrogena
Phytophthora hydropathica
Phytophthora idaei
Phytophthora ilicis
Phytophthora × incrassata
Phytophthora infestans
Phytophthora aff. infestans
Phytophthora inflata
Phytophthora insolita
Phytophthora cf. insolita
Phytophthora intercalaris
Phytophthora intricata
Phytophthora inundata
Phytophthora ipomoeae
Phytophthora iranica
Phytophthora irrigata
Phytophthora katsurae
Phytophthora kelmania
Phytophthora kernoviae
Phytophthora kwongonina
Phytophthora lactucae
Phytophthora lacustris
Phytophthora lacustris × riparia
Phytophthora lateralis
Phytophthora lilii
Phytophthora litchii
Phytophthora litoralis
Phytophthora litoralis × moyootj
Phytophthora macilentosa
Phytophthora macrochlamydospora
Phytophthora meadii
Phytophthora aff. meadii
Phytophthora medicaginis
Phytophthora medicaginis × cryptogea
Phytophthora mediterranea
Phytophthora megakarya
Phytophthora megasperma
Phytophthora melonis
Phytophthora mengei
Phytophthora mexicana
Phytophthora cf. mexicana
Phytophthora mirabilis
Phytophthora mississippiae
Phytophthora morindae
Phytophthora moyootj
Phytophthora moyootj × fluvialis
Phytophthora moyootj × litoralis
Phytophthora moyootj × thermophila
Phytophthora × multiformis
Phytophthora multivesiculata
Phytophthora multivora
Phytophthora nagaii
Phytophthora nemorosa
Phytophthora nicotianae
Phytophthora nicotianae var. parasitica
Phytophthora nicotianae × cactorum
Phytophthora niederhauserii
Phytophthora cf. niederhauserii
Phytophthora obscura
Phytophthora occultans
Phytophthora oleae
Phytophthora ornamentata
Phytophthora pachypleura
Phytophthora palmivora
Phytophthora palmivora var. palmivora
Phytophthora parasitica
Phytophthora parasitica var. nicotianae
Phytophthora parasitica var. piperina
Phytophthora parsiana
Phytophthora aff. parsiana
Phytophthora parvispora
Phytophthora × pelgrandis
Phytophthora phaseoli
Phytophthora pini
Phytophthora pinifolia
Phytophthora pisi
Phytophthora pistaciae
Phytophthora plurivora
Phytophthora pluvialis
Phytophthora polonica
Phytophthora porri
Phytophthora primulae
Phytophthora aff. primulae
Phytophthora pseudocryptogea
Phytophthora pseudolactucae
Phytophthora pseudorosacearum
Phytophthora pseudosyringae
Phytophthora pseudotsugae
Phytophthora aff. pseudotsugae
Phytophthora psychrophila
Phytophthora quercetorum
Phytophthora quercina
Phytophthora quininea
Phytophthora ramorum
Phytophthora rhizophorae
Phytophthora richardiae
Phytophthora riparia
Phytophthora rosacearum
Phytophthora aff. rosacearum
Phytophthora rubi
Phytophthora sansomea
Phytophthora sansomeana
Phytophthora aff. sansomeana
Phytophthora × serendipita
Phytophthora sinensis
Phytophthora siskiyouensis
Phytophthora sojae
Phytophthora stricta
Phytophthora sulawesiensis
Phytophthora syringae
Phytophthora tabaci
Phytophthora tentaculata
Phytophthora terminalis
Phytophthora thermophila
Phytophthora thermophila × amnicola
Phytophthora thermophila × moyootj
Phytophthora tonkinensis
Phytophthora trifolii
Phytophthora tropicalis
Phytophthora cf. tropicalis
Phytophthora tubulina
Phytophthora tyrrhenica
Phytophthora uliginosa
Phytophthora undulata
Phytophthora uniformis
Phytophthora vignae
Phytophthora vignae f. sp. adzukicola
Phytophthora virginiana
Phytophthora vulcanica
References
Further reading
Lucas, J.A. et al. (eds.) (1991) Phytophthora based on a symposium held at Trinity College, Dublin, Ireland September 1989. British Mycological Society, Cambridge University Press, Cambridge, UK, ;
Erwin, Donald C. and Ribeiro, Olaf K. (1996) Phytophthora Diseases Worldwide American Phytopathological Society Press, St. Paul, Minnesota,
Erwin, Donald C. (1983) Phytophthora: its biology, taxonomy, ecology, and pathology American Phytopathological Society Press, St. Paul, Minnesota,
"APHIS List of Regulated Hosts and Plants Associated with Phytophthora ramorum" U.S. Animal and Plant Health Inspection Services
"Dieback" Department of Environment and Conservation, Western Australia
External links
Goodwin, Stephen B. (January 2001) "Phytophthora Bibliography" Purdue University
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
Water mould plant pathogens and diseases
Water mould genera