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{{Short description|Species of single-celled organism}}
{{Speciesbox
| image = Phytophthora cactorum.jpg
| image_alt = Microscopic view of sporangium of Phytophthora cactorum
| image_caption = Microscopic view of [[sporangium]] of ''Phytophthora cactorum''
| genus = Phytophthora
| species = cactorum
| authority = ([[Hermann Lebert|Lebert]] & [[Ferdinand Cohn|Cohn]]) [[Joseph Schröter|J. Schröt.]], (1886)
| synonyms =
*''[[Peronospora]] cactorum'' Lebert & Cohn, (1870)
*''[[Phloeophthora]] cactorum'' (Lebert & Cohn) [[G.W. Wilson]], (1914)
*''Phytophthora fagi'' [[Robert Hartig|R. Hartig]], (1876)
*''Phytophthora omnivora'' [[Heinrich Anton de Bary|de Bary]], (1881)
| subdivision_ranks = Varieties
| subdivision =
*[[Phytophthora cactorum var. applanata|''Phytophthora cactorum'' var. ''applanata'']]
}}

'''''Phytophthora cactorum''''' is a fungal-like [[plant pathogen]] belonging to the [[Oomycete|Oomycota]] phylum. It is the causal agent of [[root rot]] on [[rhododendron]] and many other species, as well as leather rot of [[Strawberry|strawberries]].<ref name="Maas-1998">{{cite book | isbn=9780890541944 | title=Compendium of Strawberry Diseases | edition=2 | editor-last=Maas | editor-first=John L. | date=1998 | publisher=[[American Phytopathological Society]] Press | location=[[St. Paul, MN]] | pages=128 + 90 illustrations + 171 color plates | oclc=39641577}} {{isbn|0-89054-194-9}}.</ref>{{rp|page=33}}

==Hosts, symptoms, and diagnosis==
''Phytophthora cactorum'' has an extremely wide host range, and can infect over 200 [[species]] or 160 [[genera]] of trees, ornamentals, and fruit crops.<ref name=":2">Rivard, Cary. "''Phytophthora Cactorum''." ''Phytophthora Cactorum''. North Carolina State University, May 2007. Web.</ref> In general, ''P. cactorum'' is capable of infecting both young and old plants, and causes root rots and crown rots of the many genera it infects. Although the symptoms this pathogen produces varies between the types of organisms it infects, in general disease occurs during periods that are both wet and warm. Furthermore, most infections are caused by [[zoospore]]s entering the plant through wounds.<ref name="Maas-1998" />{{rp|page=34}}

On older trees, ''P. cactorum'' causes the formation of sap exuding dark colored [[canker]]s on the trunks of trees, as well as leaf size and number reduction, [[chlorosis]], and dieback of branches. The diagnosis of a ''P. cactorum'' infection of trees, is based on the identification of symptoms, in particular the oozing cankers, and confirmation of symptoms in a diagnosis lab or utilization of a field [[ELISA]] detection kit.<ref>"''Phytophthora'' Canker." ''Bartlett Tree Laboratories Technical Report'' (n.d.): n. pag. ''Bartlett Tree Experts''. Bartlett Tree Experts. Web.</ref> ''P. cactorum'' can be a major problem in [[apple orchard]]s, as it can cause crown, [[Collar rot|collar]], and root rots in [[apple tree]]s. When infecting apple trees, the organism can attack through wounds either above or below the soil line, impairing [[phloem]] and root function, and causing stunting, foliar disorders, and death after several years. Furthermore, because the pathogen causes damage to the phloem of the tree, one diagnostic method is to check for [[necrotic]] phloem tissue at the base of the tree which will be orange to red-brown in the early stages and dark brown in the later stages of infection.<ref name=":0" />

A good example of ''P. cactorum'' causing foliar disease is on [[ginseng]]. Foliar disease of ginseng usually occurs during May and early June, causing the leaves to become transparent and papery. Ginseng foliar infection occurs through the rain splash dispersal of spores from the soil onto above ground wounds. Once infected, ''P. cactorum'' works its way down to the roots, rotting them and killing the plant.<ref>{{Cite web|title = Foliar Phytophthora|url = http://hort.uwex.edu/articles/foliar-phytophthora/|website = Wisconsin Horticulture|access-date = 2015-11-30}}</ref>

''P. cactorum'' is also one of the causal agents of [[black rot on orchids]]. When infecting [[Orchidaceae|orchids]], this organism first produces small black lesions on the [[pseudobulb]]s of the orchid, which then enlarge and may engulf the entire pseudobulb, leaf, or move through the [[rhizome]]s to other portions of the plant prior to killing it. Diagnosis of orchid black rot by ''P. cactorum'' is through the identification of lemon-shaped [[zoosporangia]] with either a [[wikt:papilla|papilla]] or a short [[Pedicel (botany)|pedicel]], the presence of [[oospore]]s, or molecular identification. Since there are multiple species of ''[[Phytophthora]]'' that are capable of causing disease on orchids, classification only to the genus level is required for proper prescription of disease management techniques.<ref>Cating, R. A., A. J. Palmateer, C. M. Stiles, P. A. Rayside, and D. A. Davison. "Black Rot of Orchids Caused by ''[[Phytophthora palmivora]]'' and ''Phytophthora cactorum''" ''EDIS New Publications RSS''. University of Florida IFAS Extension, 2015. Web.</ref>

Crown rot or root rot of [[strawberries]] is a common example of diseases of fruit crops caused by ''P. cactorum''. On strawberries, ''P. cactorum'' infects the roots and the base of the plant causing stunting and reduced leaf size, with possible complete plant collapse later in the season. Similarly to apple trees, crown rots of strawberries caused by ''P. cactorum'' can be partially diagnosed by cutting the crown of the plant and observing brown vascular tissues, and root rots by brown or black stunted roots.<ref name=":6" />

Leather rot of [[strawberry]] is an additional disease affecting strawberry plants, with ''P. cactorum'' being the causal agent. Symptoms of this disease include brown patches or green patches with a brown border in immature fruit, with infected mature fruit displaying a purple to brown color, and becoming hard, leathery, or even mummified.<ref name=":4" /><ref name="Maas-1998" /> Signs include visible [[mycelium]] inside of hollow infected berries, as well as mycelium on the surface of berries.<ref name=":4" /><ref name="Maas-1998" /> Infected fruit often has an unpleasant taste and odor, which is diagnostic.<ref name="Maas-1998" />

==Life cycle==
''P. cactorum'' is a [[homothallic]] (only having one mating type, can mate with itself) oomycete, and displays the right angled [[mycelial]] branching with a constriction at the base of the branch, which is highly characteristic of other ''Phytophthora'' species.<ref name=":1" /> Within the [[hypha]]e, they have singular [[diploid]] [[Cell nucleus|nuclei]] that are regularly spaced. In addition, young hyphae only have cross walls separating reproductive parts; however older hyphae may have cross walls anywhere. Furthermore, although the hyphae are not the main survival unit of ''P. cactorum'', as long as they are not completely desiccated, they are capable of surviving until just above freezing temperatures.<ref name=":1">Blackwell, Elizabeth. "The Life History of ''Phytophthora cactorum''." ''Transactions British Mycological Society'' (1942): 71-89. Web.</ref>

''P. cactorum'' produces one sexually produced survival spore called an oospore, and one asexually produced survival spore called a [[chlamydospore]]. Oospores are double-walled and [[uninucleate]] during dormancy, but become [[multinucleate]] in preparation for germination. In contrast, the chlamydospores have only one resistant wall and are multinucleate at all stages. Chlamydospores are larger than oospores in size, and are only formed under certain environmental triggers. The trigger for preferential formation of chlamydospores over oospores can be either large temperature or moisture oscillations.<ref name=":1" />

In addition to the chlamydospore, ''P. cactorum'' also produces another asexual spore called a [[sporangium]]. A sporangia is a multinucleate dispersal structure with a thin wall and papilla that is formed on a [[sporangiophore]]. Although the size may vary based on the environmental conditions in which they are formed, the width of a sporangia is always more than 2/3 times than its length. Depending on moisture conditions, sporangia can either germinate or release zoospores.<ref name=":1" />

Zoospores are produced in wet conditions by either oospores or sporangia.<ref name=":0" /> ''Phytophthora cactorum'' zoospores, are uninucleate, laterally [[biflagellate]], and pear- or lemon-shaped. After being released, zoospores swim to a nearby wound on a suitable host, germinate, and enter wounds to cause a hyphal infection of the roots or crown vascular system.<ref name=":1" />

In Leather Rot of Strawberry, ''P. cactorum'' raindrop splash is required to spread the zoospores to the strawberry fruit, unless flood conditions cause the zoospores to be able to swim directly to the fruit.<ref name=":4">{{Cite web |last=Gubler |first=W.D. |date= July 2018 |title=Leather Rot |url=https://www2.ipm.ucanr.edu/agriculture/strawberry/leather-rot/ |access-date=3 May 2022 |website=UC IPM}}</ref>

== Environment ==
Because ''Phytophthora'' is a soilborne pathogen, the ideal condition for ''P. cactorum'' growth is in saturated soil.<ref name=":6" /> ''P. cactorum'' stays in the soil as dormant resting oospores and chlamydospores, or within infected plant tissue. When conditions are met and the soil is wet enough, sporangia are produced, carrying on the life cycle of the pathogen. The minimum amount of time the plant must be saturated to produce an infection depends on factors such as genetics, physiological processes, and the environment. However, when a plant is allowed to sit in soil that is heavy and soggy for long periods of time, the chance of infection is increased. A plant's inability to fight off the pathogen is impeded when saturated soil conditions limit the amount of available oxygen for its roots. In many cases, most host plants are the most susceptible to infection during spring and autumn when the soil is wetter and at a more ideal temperature for zoospore production and activity.<ref>{{Cite journal|url = http://nysipm.cornell.edu/factsheets/treefruit/diseases/phyt/phyt.asp|title = ''Phytophthora'' Root and Crown Rot|date = 1992|website = New York State Integrated Pest Management Program|last = Wilcox|first = Wayne F.}}</ref>

==Importance==
''P. cactorum'' was first described in 1870 as a [[cactus]] pathogen.<ref>{{Cite web|title = ''Phytophthora cactorum''|url = http://forestphytophthoras.org/species/cactorum|website = Forest Phytophthoras of the World|last = Hudler|first = G. W.|date = 2015}}</ref> Since then, it has been found to not only infect cacti, but a wide range of plants worldwide. ''P. cactorum'' was first reported in the [[United States]] in 1858 when infected apple trees were discovered in [[Michigan]].<ref>{{Cite book|title = Biological Control Programmes in Canada: 1981-2000|url = https://archive.org/details/biologicalcontro00maso|url-access = limited|last1 = Mason|first1 = Peter George|publisher = CABI|year = 2002|location = Oxon., Eng.|pages = [https://archive.org/details/biologicalcontro00maso/page/n480 475]|first2 = John T.|last2 = Huber|chapter = ''Phytophthora cactorum'' (Lebert and Cohn) Schröter, Crown and Root Rot (Pythiaceae)| isbn=9780851995274 }}</ref> By 1928, it had spread to [[Canada]] in the [[Okanagan Valley]], [[British Columbia]]. Since then, it has caused around C$2 million in damage per year.{{citation needed|date=May 2022}}

The importance of this oomycete is its vast host range and the damage it causes to major crops. This pathogen can cause root rot that stunts the host's growth and damages vascular tissue, which is especially detrimental to [[pear]] and apple orchards. It can also infect strawberry plants and cause [[crown rot]], root rot, and leather rot of the fruit.<ref name=":0">{{Cite web|url = http://www.cals.ncsu.edu/course/pp728/cactorum/images/apple_root_rot.gif|title = ''Phytophthora'' Root Rot of Apple|date = 1990|website = NC State University Department of Plant Pathology|last = Fujita|first = D.B.}}</ref> This pathogen causes millions of dollars in damage, and disease management such as soil fumigation is also expensive.

==Disease management and control==
The best way to manage ''P. cactorum'' is by implementing an integrated management plan. The combination of soil [[fumigation]] and proper cultural controls will be the best option for plant health. Recommended chemical controls products include [[fosetyl-Al]], [[metalaxyl]], and [[etridiazole]]. Prevention and [[sanitation]] are crucial because this pathogen is usually transmitted through cuts or injuries on the plant. The spores are easily transported through [[irrigation]] water and will splash to nearby plants. Elevating your plants above the ground can help to prevent infection. The pathogen thrives in moist soils therefore it is important to avoid very saturated soils as much as possible and one should work to prepare their soil for adequate drainage during the wet periods. Soil drainage and low soil [[pH]] may help to reduce the disease.<ref name=":2" /> [[Fertilizer]] regimen methods have been used to control against ''P. cactorum''. These fertilizers include organic materials that release [[ammonia]], [[nitrous acid]], and amendments to reduce the pH to less than 4.<ref name=":6">{{Cite web|url = http://www.ipm.ucdavis.edu/PMG/r734100911.html|title = ''Phytophthora'' Crown Rot|date = June 2008|website = University of California Statewide Integrated Pest Management Program|last1 = Koike|first1 = S.T.|last2 = Browne|first2 = G.T.|last3 = Gordon|first3 = T.R.|last4 = Gubler|first4 = W.D.}}</ref> The use of [[raised bed]]s and a carefully managed [[drip irrigation]] system will be important cultural practices that can be implemented.<ref name=":6" /> There are some form of [[biological control]]s that have been found to be somewhat successful with ''[[Enterobacter aerogenes]]'' and ''[[Trichoderma]]''.<ref name=":2" />

==Pathogenesis==
When able to culture the ''P. cactorum'' on different media, it will produce a [[maple]] wilt associated [[phytotoxin]]. These phytotoxins cause browning of veins, desiccation of apple leaves, and wilting of [[tomato]] cuttings.<ref name=":3">{{cite journal |last1=Plich |first1=Miroslawa |last2=Rudnicki |first2=Ryszard M. |title=Studies of the Toxins of ''Phytophthora cactorum'' Pathogenic to Apple Trees |date=March 1979 |journal=Journal of Phytopathology |volume=94 |issue=3 |pages=270–278 |issn=0031-9481 |doi=10.1111/j.1439-0434.1979.tb01559.x|bibcode=1979JPhyt..94..270P }}</ref> Studies have shown that this the ''P. cactorum'' phytotoxin is [[hydrophilic]] in nature and will not move to the organic solvents. The chemical properties of this toxin seem to be similar to those of other ''Phytopthora'' species. Within the plant, the ''P. cactorum'' phytotoxin is most likely [[xylem]] transported through and can accumulate in the space in between leaves where it causes desiccation and withering.<ref name=":3" />

A toxin protein similar to other oomycete [[Elicitin|elicitins]] based on apparent molecular weight, isoelectric point, amino acid composition, and host pathology induction activity was isolated from ''P. cactorum'' culture.<ref>{{cite journal |last1=Dubery |first1=Ian |last2=Meyer |first2=Debra |last3=Bothma |first3=Chris |title=Purification and characterization of cactorein, a phytotoxin secreted by ''Phytophthora cactorum'' |journal=Phytochemistry |date=1994 |volume=35 |issue=2 |pages=307–312 |doi=10.1016/S0031-9422(00)94753-8 |bibcode=1994PChem..35..307D |url=https://www.sciencedirect.com/science/article/abs/pii/S0031942200947538 |access-date=24 January 2025|url-access=subscription }}</ref> The whole genome sequence of a then-new isolate of ''P. cactorum'' was obtained in 2018, revealing 39 elicitin genes in that isolate.<ref>{{cite journal |last1=Yang |first1=Min |last2=Duan |first2=Shengchang |last3=Mei |first3=Xinyue |last4=Huang |first4=Huichuan |last5=Chen |first5=Wei |last6=Liu |first6=Yixiang |last7=Guo |first7=Cunwu |last8=Yang |first8=Ting |last9=Wei |first9=Wei |last10=Liu |first10=Xili |last11=He |first11=Xiahong |last12=Dong |first12=Yang |last13=Zhu |first13=Shusheng |title=The ''Phytophthora cactorum'' genome provides insights into the adaptation to host defense compounds and fungicides |journal=Scientific Reports |date=25 April 2018 |volume=8 |issue=1 |page=6534 |doi=10.1038/s41598-018-24939-2 |pmid=29695739 |pmc=5916904 |bibcode=2018NatSR...8.6534Y }}</ref> Numerous isolates of ''P. cactorum'' have been described, however, and the specific toxins affecting specific plants have not been well-studied.<ref>{{cite journal |last1=Chen |first1=Xiao-Ren |last2=Wen |first2=Ke |last3=Zhou |first3=Xue |last4=Zhu |first4=Ming-Yue |last5=Liu |first5=Yang |last6=Jin |first6=Jing-Hao |last7=Nellist |first7=Charlotte F. |title=The devastating oomycete phytopathogen ''Phytophthora cactorum'': Insights into its biology and molecular features |journal=Molecular Plant Pathology |date=September 2023 |volume=24 |issue=9 |pages=1017–1032 |doi=10.1111/mpp.13345 |pmid=37144631|pmc=10423333 |bibcode=2023MolPP..24.1017C }}</ref>

In pathogenicity tests on strawberry plants in a greenhouse, the fruit isolates caused little disease, while strawberry root system isolates were highly aggressive.<ref name=":5">R. G. Bhat, P. M. Colowit, T. H. Tai, M. K. Aradhya, and G. T. Browne. "Genetic and Pathogenic Variation in ''Pythophthora cactorum'' Affecting Fruit and Nut Crops in California." ''The American Phytopathological Society (2006).''</ref> ''P. cactorum'' phytotoxin is thought to have a role in disease development and pathogenesis, however further study is required.

==References==
{{Reflist}}

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{{DEFAULTSORT:Phytophthora Cactorum}}
[[Category:Phytophthora|cactorum]]
[[Category:Water mould plant pathogens and diseases]]
[[Category:Ornamental plant pathogens and diseases]]

Phytophthora cactorum - Revision history

imported>OAbot: Open access bot: url-access updated in citation with #oabot.