Molecular Biology and Genetics

Molecular Biology

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Specimen Records:704
Specimens with Sequences:1199
Specimens with Barcodes:598
Species With Barcodes:126
Public Records:693
Public Species:126
Public BINs:113
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Sudden Oak Death caused by Phytophthora ramorum

Phytophthora (from Greek φυτόν (phytón), “plant” and φθορά (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 cell wall of Phytophthora is made up of cellulose. The genus was first described by Heinrich Anton de Bary in 1875. Approximately 100 species have been described, although 100-500 undiscovered Phytophthora species are estimated to exist.[3]


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 the most destructive pathogen of solanaceous crops, including tomato and potato.[4] 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:

Research beginning in the 1990s has placed some of the responsibility for European forest die-back on the activity of imported Asian Phytophthoras.[7]

Fungi resemblance[edit]

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, chromalveolatas are more closely related to plants than animals. Whereas fungal cell walls are made primarily of chitin, chromalveolata cell walls are constructed mostly of cellulose. Ploidy levels are different between these two groups; Phytophthora have diploid (paired) chromosomes in the vegetative (growing, non-reproductive) stage of life, Fungi are almost always haploid in this state. Biochemical pathways also differ, notably the highly conserved Lysine synthesis path.


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.

The life cycle of Phytophthora

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


  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. Retrieved 2009-06-05. 
  2. ^ Hansen, Everett M.; Reeser, P. W.; Davidson, J. M.; Garbelotto, Matteo; Ivors, K.; Douhan, L.; Rizzo, David M. (2003). "Phytophthora nemorosa, a new species causing cankers and leaf blight of forest trees in California and Oregon, U.S.A" (PDF). Mycotaxon 88: 129–138. 
  3. ^ Brasier CM, 2009. Phytophthora biodiversity: how many Phytophthora species are there? In: Goheen EM, Frankel SJ, eds. Phytophthoras in Forests and Natural Ecosystems. Albany, CA, USA: USDA Forest Service: General Technical Report PSW-GTR-221, 101–15.
  4. ^ Nowicki, Marcin et al. (17 August 2011), Potato and tomato late blight caused by Phytophthora infestans: An overview of pathology and resistance breeding, Plant Disease, ASP, doi:10.1094/PDIS-05-11-0458, retrieved 2011-08-30 
  5. ^ Brasier, C; Beales, PA; Kirk, SA; Denman, S; Rose, J (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 (Pt 8): 853–9. doi:10.1017/S0953756205003357. PMID 16175787. 
  6. ^ "APHIS List of Regulated Hosts and Plants Associated with Phytophthora ramorum" U.S. Animal and Plant Health Inspection Services;
  7. ^ "Phytophthora: Asiatischer Pilz lässt die Bäume sterben" Süddeutschen Zeitung 11 May 2005

Further reading[edit]

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