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Phytophthora

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File:Phytophthora kernoviae Rhododendron.jpg
Rhododendron ponticum showing classic symptoms of Phytophthora kernoviae in the UK

Phytophthora (from Greek {{#invoke:Lang|lang}} (phytón), "plant" and {{#invoke:Lang|lang}} (Template:Transliteration), "destruction"; "the plant-destroyer") is a genus of plant-damaging oomycetes (water molds), whose member species cause 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.<ref>Brasier CM, 2009. Phytophthora biodiversity: how many Phytohthora species are there? In: Goheen EM, Frankel SJ, eds. Phytophthoras in Forest and Natural Ecosystems. Albany, CA, USA: USDA Forest Service: General Technical Rep rt PSW-GTR-221, 101–15.</ref>

PathogenicityEdit

File:SuddenOakDeath-USDA-Forest-Service.jpg
Sudden oak death caused by Phytophthora ramorum

Phytophthora spp. are mostly pathogens of dicotyledons, and many are relatively host-specific parasites. P. 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. P. 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.<ref name="PlDis2011">Ristaino, J. B., Cooke, D.E.L., Acuña, I., Muñoz, M. 2020. The Threat of Late Blight to Global Food Security. Pages 101-133 in: In Emerging Plant Disease and Global Food Security. A. Records and J. B. Ristaino, eds. American Phytopathological Society Press, St. Paul. https://doi.org/10.1094/9780890546383.006</ref> The soya bean root and stem rot agent, P. sojae, 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:

Research beginning in the 1990s placed some of the responsibility for European forest die-back on the activity of imported Asian Phytophthoras.<ref>"Phytophthora: Asiatischer Pilz lässt die Bäume sterben" Süddeutschen Zeitung 11 Ma 2005</ref>

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 P. 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.<ref>Template:Cite journal</ref>

ReproductionEdit

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.<ref name="P-frag" /> Phytophthora zoospores recognize and attach to specific root surface regions.<ref name="P-frag" /> This is a high degree of specificity at an early stage of cell development.<ref name="P-frag">Template:Cite book</ref>

File:Phytophthora life cycle.png
The lifecycle of Phytophthora
File:Phytophtora reproduction.png
Phytophthora forms: A: Sporangia. B: Zoospore. C: Chlamydospore. D: Oospore

Evolution and resemblance to fungiEdit

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.Template:Citation needed.

SpeciesEdit

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Phytophthora betacei

|CitationClass=web }}</ref><ref>Man in 't Veld, W.A. et al. 2019. Multiple Halophytophthora spp. and Phytophthora spp. including P. gemini, P. inundata and P. chesapeakensis sp. nov. isolated from the seagrass Zostera marina in the Northern hemisphere. Eur J Plant Pathol 153: 341-357. {{#invoke:doi|main}}</ref>

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ReferencesEdit

Template:Reflist<ref>Coomber, A., Saville, A., Carbone, I. and Ristaino, J. 2023. An open T base phylogeny for emerging Phytophthora species.  Plos One: https://doi.org/10.1371/journal.pone.0283540

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Further readingEdit

External linksEdit

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