Plant pathology
147484
223527611
2008-07-04T13:32:15Z
PilcrowPi
7375641
/* Parasitic plants */
{{Farming}}
''For the journal, see [[Plant Pathology (journal)]].''
'''Plant pathology''' (also called phytopathology) is the scientific study of plant diseases caused by pathogens (infectious diseases) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Not included are insects, mites, vertebrate or other pests that affect plant health by consumption of plant tissues. Plant pathology also involves the study of the identification, etiology, disease cycle, economic impact, epidemiology, how plant diseases affect humans and animals, pathosystem genetics and management of plant diseases. </onlyinclude>
==Plant pathogens==
The ''"Disease triangle"'' is a central concept of plant pathology for infectious diseases<ref name=Arios>George N. Agrios (1997) Plant Pathology fourth edition, Academic Press. New York.</ref> . It is based on the principle that disease is the result of an interaction between a host, a pathogen, and environment condition.
===Fungi===
[[Image:Powdery mildew.JPG|thumb|left|[[Powdery mildew]], a Biotrophic Fungus]]
[[Image:Rice blast.jpg|thumb|left|[[Rice blast]], a necrotrophic fungus]]
The majority of phytopathogenic fungi belong to the [[Ascomycetes]] and the [[Basidiomycetes]].
The fungi reproduce both [[sexually]] and [[asexually]] via the production of [[spores]]. These spores may be spread long distances by air or water, or they may be soil bourne. Many soil bourne spores, normally [[zoospores]] and capable of living [[saprotroph|saprotrophically]], carrying out the first part of their lifecycle in the [[soil]].
Fungal diseases can be controlled through the use of [[fungicides]] in agriculture, however new [[Race (biology)|races]] of fungi often [[evolution|evolve]] that are resistant to various fungicides.
Significant fungal plant pathogens
====Ascomycetes====
**''[[Fusarium]]'' spp.
**''[[Thielaviopsis]]'' spp. (Causal agents of: canker rot, black root rot, ''Thielaviopsis'' root rot)
**''[[Verticillium]]'' spp.
**''[[Magnaporthe grisea]]'' (T.T. Hebert) M.E. Barr; causes blast of rice and gray leaf spot in turfgrasses
====Basidiomycetes====
**''[[Rhizoctonia]]'' spp.
**''[[Soybean rust|Phakospora pachyrhizi]]'' Sydow; causes Soybean rust
**''Puccinia'' spp.; causal agents of severe rusts of virtually all cereal grains and cultivated grasses
===Oomycetes===
The [[oomycetes]] are fungal-like organisms that until recently used to be mistaken for [[fungi]]. They include some of the most destructive plant pathogens including the [[genus]] ''Phytophthora'' which includes the casual agents of [[Phytophthora infestans|potato late blight]] and [[sudden oak death]].
Despite not being closely related to the fungi, the oomycetes have developed very similar infection strategies and so many plant pathologists group them with fungal pathogens.
Significant oomycete plant pathogens
*''[[Pythium]]'' spp.
*''[[Phytophthora]]'' spp.; including the causal agent of the [[Great Irish Famine|Great Irish Famine (1845-1849)]]
Rice blast is hemibiotrophic
===Bacteria===<!-- This section is linked from [[Bacterial Plant Pathogen]] -->
[[Image:Agrobacteriumgall.jpg|thumb|Crown gall disease caused by [[Agrobacterium]]]]
Most [[bacteria]] that are associated with plants are actually [[saprotrophic]], and do no harm to the plant itself. However, a small number, around 100 species, are able to cause disease. Bacterial diseases are much more prevalent in [[sub-tropical]] and [[tropical]] regions of the world.
Most plant pathogenic bacteria are rod shaped ([[Bacteria#Morphology|bacilli]]). In order to be able to colonise the plant they have specific pathogenicity factors. There are 4 main bacterial pathogenicity factors:
1. '''Cell wall degrading enzymes''' - used to break down the plant [[cell wall]] in order to release the nutrients inside. Used by pathogens such as [[Erwinia]] to cause [[soft rot]].
2. '''[[Toxins]]''' These can be non-host specific, and damage all plants, or host specific and only cause damage on a host plant.
3. '''[[Phytohormones]]''' - for example [[Agrobacterium]] changes the level of [[Auxin]] to cause tumours.
4. '''[[Exopolysaccharides]]''' - these are produced by bacteria and block [[xylem]] vessels, often leading to the death of the plant.
Bacteria control the production of [[pathogenicity factors]] via [[quorum sensing]].
Significant bacterial plant pathogens
*[[Proteobacteria]]
**''[[Xanthomonas]]'' spp.
**''[[Pseudomonas]]'' spp.
====Phytoplasmas ('Mycoplasma-like organisms') and spiroplasmas====
{{main|phytoplasma}}
[[Image:Vitis vinifera phytoplasma.jpg|thumb|[[Vitis vinifera]] with "Ca. Phytoplasma vitis" infection]]
''[[Phytoplasma]]'' and ''[[Spiroplasma]]'' are a genre of bacteria that lack cell walls, and are related to the [[mycoplasmas]] which are human pathogens. Together they are referred to as the [[mollicutes]]. They also tend to have smaller [[genomes]] than true bacteria. They are normally transmitted by sap-sucking [[insects]], being transferred into the plants [[phloem]] where it reproduces.
===Viruses, viroids and virus-like organisms===
{{main|Plant Virus}}
[[Image:Pepper mild mottle virus.png|thumb|left|[[Capsicum|Pepper]] mild mottle virus]]
There are many types of [[plant virus]], and some are even [[asymptomatic]]. Normally plant viruses only cause a loss of [[yield]]. Therefore it is not economically viable to try to control them, the exception being when they infect [[perennial plant|perennial]] species, such as fruit trees.
Most plant viruses have small, single stranded [[RNA]] genomes. These genomes may only encode 3 or 4 [[proteins]]: a [[replicase]], a coat protein, a movement protein to allow cell to cell movement and sometimes a protein that allows transmission by a vector.
Plant viruses must be transmitted from plant to plant by a [[Vector (biology)|vector]]. This is normally an insect, but some [[fungi]], [[nematodes]] and [[protozoa]] have been shown to be viral vectors.
===Nematodes===
[[Image:Nematode nodules.jpg|right|thumb|200px|[[Root-knot nematode]] galls]]
[[Nematodes]] are small, multicelluar wormlike creatures. Many live freely in the soil, but there are some species which parasitize plant [[root]]s. They are mostly a problem in [[tropical]] and [[subtropical]] regions of the world, where they may infect [[crops]]. Root knot nematodes have quite a large host range, whereas cyst nematodes tend to only be able to infect a few species. Nematodes are able to cause radical changes in root cells in order to facilitate their lifestyle.
===Protozoa===
There are a few examples of plant diseases caused by [[protozoa]]. They are transmitted as [[zoospores]] which are very durable, and may be able to survive in a resting state in the soil for many years. They have also been shown to transmit plant [[viruses]].
When the motile zoospores come into contact with a [[root hair]] they produce a plasmodium and invade the [[root]]s.
===Parasitic plants===
Parasitic plants such as [[mistletoe]] and [[Cuscuta|dodder]] are included in the study of phytopathology. Dodder, for example, is used as a conduit for the transmission of virues or virus-like agents from a host plant to either a plant that is not typically a host or for an agent that is not graft-transmissible.
== Physiological plant disorders ==
{{Main|Physiological plant disorders}}
Significant abiotic disorders can be caused by:
:'''''Natural'''''
::[[Drought]]
::[[Frost]] damage, and breakage by [[snow]] and [[hail]]
::[[Flood]]ing and poor drainage
::[[Nutrient]] deficiency
::[[Sodium chloride|Salt]] deposition and other soluble mineral excesses (e.g. [[gypsum]])
::[[Wind]] (windburn, and breakage by [[hurricane]]s and [[tornado]]es)
::[[Lightning]] and [[wildfire]] (also often man-made)
:'''''Man-made''''' (arguably not abiotic, but usually regarded as such)
::[[Soil]] compaction
::[[Pollution]] of air and/or soil
::[[Sodium chloride|Salt]] from winter road salt application
::[[Herbicide]] over-application
::Poor education and training of people working with plants (e.g. lawnmower damage to trees)
::[[Vandalism]]
== Epidemiology ==
{{main|Plant Disease Epidemiology}}
==Management==
{{Expand-section|date=January 2007}}
*Quarantine
*Cultural
*Plant resistance
*Chemical
*Biological
*Integrated
==See also==
* [[American Phytopathological Society]]
* [[Biological Control]]
* [[British Society for Plant Pathology]]
* [[burl]]
* [[Common names of plant diseases]]
* [[Fungicide]]s
* [[Gene-for-gene relationship]]
* [[Global Plant Clinic]]
* [[Herbivory]]
* [[List of phytopathology journals]]
* [[Mycology]]
* [[Pesticide]]
* [[Plant disease forecasting]]
* [[QoI]]
* [[Phytoplasma]]
* [[Plant virus]]
* [[Strobilurin]]s
* [[Stunt (botany)|Stunt]]
==References==
{{reflist|2}}
<!--
Using this template per Wikipedia:Citation templates
{{cite news |first= |last= |authorlink= |author= |coauthors= |title= |url= |format= |work= |publisher= |id= |pages= |page= |date= |accessdate= |language= |quote= }}
...OR...
{{cite web |url= |title= |accessdate= |accessmonthday= |accessdaymonth= |accessyear= |author= |last= |first= |authorlink= |coauthors= |date= |year= |month= |format= |work= |publisher= |pages= |language= |doi= |archiveurl= |archivedate= |quote= }}
...OR...
{{cite journal |last= |first= |authorlink= |coauthors= |year= |month= |title= |journal= |volume= |issue= |pages= |id= |url= |accessdate= |quote= }}
...OR....
{{cite book |last= |first= |authorlink= |coauthors= |editor= |others= |title= |origdate= |origyear= |origmonth= |url= |format= |accessdate= |accessyear= |accessmonth= |edition= |series= |date= |year= |month= |publisher= |location= |language= |isbn= |oclc= |doi= |id= |pages= |chapter= |chapterurl= |quote= }}
-->
==Further reading==
{{Horticulture and Gardening}}
==External links==
* [http://www.apsnet.org/ American Phytopathological Society]
* [http://www.bspp.org.uk/ British Society for Plant Pathology]
* [http://www.plantmanagementnetwork.org/php/ Plant Health Progress, Online journal of applied plant pathology]
* [http://www.pnwfungi.org/ Pacific Northwest Fungi, online mycology journal with papers on fungal plant pathogens]
* [http://www.rothamsted.bbsrc.ac.uk/ppi Rothamsted Plant Pathogen Interactions Department]
* [http://winegrapes.wsu.edu/virology/ Grape Virology]
[[Category:Phytopathology]]
[[Category:Plant pathogens and diseases|*]]
[[Category:Agronomy]]
[[Category:Microbiology]]
[[bg:Фитопатология]]
[[ca:Fitopatologia]]
[[da:Plantesygdom]]
[[de:Phytopathologie]]
[[es:Fitopatología]]
[[eo:Fitopatologio]]
[[fa:گیاهپزشکی]]
[[fr:Pathologie végétale]]
[[id:Fitopatologi]]
[[it:Patologia vegetale]]
[[lt:Augalų ligos]]
[[mk:Фитопатологија]]
[[ms:Fitopatologi]]
[[nl:Fytopathologie]]
[[ja:植物病理学]]
[[pl:Fitopatologia]]
[[pt:Fitopatologia]]
[[ro:Fitopatologie]]
[[ru:Фитопатология]]
[[simple:Plant pathology]]
[[sk:Fytopatológia]]
[[su:Pitopatologi]]
[[fi:Kasvipatologia]]
[[vi:Bệnh học thực vật]]