Phytophthora

Phytophthora
Phytophthora porri on leek (Allium porrum)
Scientific classification
Domain: Eukaryota Kingdom: Chromalveolata Phylum: Heterokontophyta Class: Oomycetes Order: Peronosporales Family: Pythiaceae Genus: Phytophthora
Species
Phytophthora botryosa Phytophthora brassicae Phytophthora cactorum Phytophthora cajani Phytophthora cambivora Phytophthora capsici Phytophthora cinnamomi Phytophthora citricola Phytophthora citrophthora Phytophthora clandestina Phytophthora colocasiae Phytophthora cryptogea Phytophthora drechsleri Phytophthora erythroseptica Phytophthora fragariae Phytophthora gonapodyides Phytophthora heveae Phytophthora humicola Phytophthora hydropathica[1] Phytophthora irrigata[1] Phytophthora idaei Phytophthora ilicis Phytophthora infestans Phytophthora inflata Phytophthora iranica Phytophthora katsurae Phytophthora lateralis Phytophthora medicaginis Phytophthora megakarya Phytophthora megasperma Phytophthora melonis Phytophthora mirabilis Phytophthora multivesiculata Phytophthora nemorosa[2] Phytophthora nicotianae Phytophthora palmivora Phytophthora phaseoli Phytophthora porri Phytophthora primulae Phytophthora pseudotsugae Phytophthora quercina Phytophthora ramorum Phytophthora sinensis Phytophthora sojae Phytophthora syringae Phytophthora tentaculata Phytophthora trifolii Phytophthora vignae

Sudden Oak Death caused by Phytophthora ramorum

Phytophthora (from Greek phytón, “plant” and phthorá, “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 genus was first described by Heinrich Anton de Bary in 1875.

Pathogenicity

Phytophthora spp. are mostly pathogens of dicotyledons, and are relatively host-specific parasites. 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 Irish Famine (1845-1849), and still remains to be the most destructive pathogen of potato crops, and 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, and thus the growth of resistant cultivars is the main management strategy. Other important Phytophthora diseases are:

• Phytophthora alni – causes alder root rot
• Phytophthora cactorum – causes rhododendron root rot affecting rhododendrons, azaleas and causes bleeding canker in hardwood trees
• Phytophthora capsici - infects Cucurbitaceae fruits, such as cucumbers and squash
• Phytophthora cinnamomi - causes cinnamon root rot affecting woody ornamentals including arborvitae, azalea, Chamaecyparis, dogwood, forsythia, Fraser fir, hemlock, Japanese holly, juniper, Pieris, rhododendron, Taxus, white pine, American chestnut and Australian Jarrah.
• Phytophthora fragariae - causes red root rot affecting strawberries
• 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.^[3]
• 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^[4]
• 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.^[5]

Fungi resemblance

Phytophthora is sometimes referred to as a fungal-like organism but it is classified under a different kingdom altogether: Chromalveolata (formerly Stramenopila and previously Chromista). This is a good example of convergent evolution: Phytophthora is morphologically very similar to true fungi yet its evolutionary history is quite distinct. In contrast to fungi, stramenopiles are more closely related to plants than animals. Whereas fungal cell walls are made primarily of chitin, stramenopile cell walls are constructed mostly of cellulose. Ploidy levels are different between these two kingdoms as are biochemical pathways.

Biology

Phytophthoras 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 its role as a survival structure. Sporangia may be retained by the subtending hyphae (non-caducous) 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.

Phytophthora forms: A: Sporangia. B: Zoospore. C: Chlamydospore. D: Oospore.

Notes

1. ^ ^{a b} Hong, C; Gallegly, M, Richardson, P, Kong, P, Moorman, G, Lea-Cox, J, Ross, D (June 2008). "Phytophthora irrigata and Phytophthora hydropathica, two new species from irrigation water at ornamental plant nurseries". Phytopathology Vol. 98, no. 6. http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=8354020&q=Phytophthora+drechsleri&uid=1337633&setcookie=yes. Retrieved 2009-06-05. 
2. ^ Hansen, Everett M.; Reeser, P. W.; Davidson, J. M.; Garbelotto, Matteo; Ivors, K.; Douhan, L.; and Rizzo, David M. (2003) "Phytophthora nemorosa, a new species causing cankers and leaf blight of forest trees in California and Oregon, U.S.A Mycotaxon 88: pp. 129-138
3. ^ Brasier, C (2005), "Phytophthora kernoviae sp. Nov., an invasive pathogen causing bleeding stem lesions on forest trees and foliar necrosis of ornamentals in the UK", Mycological Research 109: 853, doi:10.1017/S0953756205003357, http://www.forestry.gov.uk/pdf/P_kernoviae_paper_2005.pdf/$FILE/P_kernoviae_paper_2005.pdf 
4. ^ "APHIS List of Regulated Hosts and Plants Associated with Phytophthora ramorum" U.S. Animal and Plant Health Inspection Services;
5. ^ "Phytophthora: Asiatischer Pilz lässt die Bäume sterben" Süddeutschen Zeitung 11 May 2005

References

• 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, ISBN 0-521-40080-5 ;
• Erwin, Donald C. and Ribeiro, Olaf K. (1966) Phytophthora Diseases Worldwide American Phytopathological Society Press, St. Paul, Minnesota, ISBN 0-89054-212-0
• Erwin, Donald C. (1983) Phytophthora: its biology, taxonomy, ecology, and pathology American Phytopathological Society Press, St. Paul, Minnesota, ISBN 0-89054-050-0
• "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;