Fusarium oxysporum: Difference between revisions

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[11] http://www.extento.hawaii.edu/kbase/crop/type/f_oxys.htm <br>
[11] http://www.extento.hawaii.edu/kbase/crop/type/f_oxys.htm <br>
[12] http://www.cabi.org/dmpd/default.aspx?site=165&page=4050&LoadModule=Review&ReviewID=170522 <br>
[12] http://www.cabi.org/dmpd/default.aspx?site=165&page=4050&LoadModule=Review&ReviewID=170522 <br>
[13]
[13] http://sciweb.nybg.org/science2/hcol/fusarium3.asp <br>
[14] <br>


==Author==
==Author==

Revision as of 02:57, 15 April 2011

This student page has not been curated.
A culture of F. oxysporum displays it's purple pigmentation [2]

Classification

Superkingdom: Eukaryota; Kingdom: Fungi; Phylum: Ascomycota; Class: Sordariomycetes; Order: Hypocreales; Genus: Fusarium

Species

NCBI: Taxonomy

Fusarium oxysporum

Fusarium2.jpg

Description and Significance

Describe the appearance, habitat, etc. of the organism, and why you think it is important.
Appearance


Habitat
F. oxysporum appears to be largely cosmopolitan meaning that it can be found almost everywhere, with higher concentrations of the various Formae speciales in different areas across the globe. Distribution maps show that this fungus has invaded North and South America, Europe, Africa, Asia, and Oceania [12].

Genome Structure

Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence?


Cell Structure, Metabolism and Life Cycle

Interesting features of cell structure; how it gains energy; what important molecules it produces.

This image shows the microconidia of F. oxysporum. These are the tiny asexual fungal spores that function as its mode of reproduction. [2]

F. oxysporum is a rapidly growing colony, which can expand to 4.5 cm in a few days.

F. oxysporum can survive non-pathogenetically as a mycelium, complete with a mass of hyphae, in soil with organic matter. It is a saprophyte, or a heterotroph that can obtain nutrients by consuming detritus (decomposing organic matter). F. oxysporum can also utilize three types of asexual spores:

  • Microconidia - The smaller sized conidia, one or two celled, more abundant and frequently produced by the fungus under all conditions. It is also the type of spore most frequently produced within the vessels of infected plants.
  • Macroconidia - The larger conidia, which are three to five celled, gradually pointed and curved toward the ends. These spores are commonly found on the surface of plants killed by this pathogen as well as in sporodochia-like groups.
  • Chlamydospores - Have one or two cells, are round, thick-walled spores, produced either terminally or intercalary on older mycelium or in macroconidia. Remarkably, they can remain dormant in soil and infect other hosts for as long as 30 years [13].

These spores can be spread short distances by irrigation water and contaminated farm equipment; or long distances by infected transplants, via wind, and rarely from contaminated seeds from infected fruits [11].

Disease Cycle
Healthy plants are infected by F. oxysporum when the soil in which they are growing is contaminated with the fungus. The fungus proceeds to invade the plant either with its sporangial germ tube or mycelium by invading the plant's roots. The roots can be infected directly through the root tips, through wounds in the roots, or at the formation point of lateral roots. Once inside the plant, the mycelium grows through the root cortex intercellulary. When the mycelium reaches the xylem, it invades the vessels through the xylem's pits. At this point, the mycelium remains in the vessels, where it usually advances upwards toward the stem and crown of the plant. As it grows, the mycelium branches and produces microconidia, which are carried upward within the vessel by way of the plant's sap stream. When the microconidia germinate, the mycelium can penetrate the upper wall of the xylem vessel, enabling more microconidia to be produced in the next vessel. The fungus can also advance laterally as the mycelium penetrates the adjacent xylem vessels through the xylem pits [11].

Ecology and Pathogenesis

Habitat; symbiosis; biogeochemical significance; contributions to environment.
If relevant, how does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

This image portrays the damage F. oxysporum can have on crops [1]
F. oxysporum tends to leave its victims a yellow or brown color [3]

Fusarium oxysporum has many Formae speciales (special forms) that exist as plant pathogens, causing storage, root, stem, and fruit rot, as well as vascular wilt. They are also important mycotoxin (toxic metabolite) producers. These various special forms infect certain crops:

  • F. oxysporum f.sp. cubense causes Banana wilt
  • F. oxysporum f.sp. vasinfectum causes wilt of cotton
  • F. oxysporum f.sp. batatas causes wilt of sweet potatoes and stem rot
  • F. oxysporum f.sp. lycopersici causes tomato wilt
  • F. oxysporum f.sp. asparagi causes asparagus wilt
  • F. oxysporum f.sp. melonis causes muskmelon wilt
  • F. oxysporum f.sp. zingiberi causes ginger wilt

In general, the fungi manages to infect the vascular system of the plant, where it wreaks havoc. This infiltration to the vascular system affects the plant's water supply greatly. A lack of water ensues, inducing the leaves' stomata to close and the leaves to wilt. At this point you can see the outward signs of fusarium wilt, as the leaves turn yellow or brown before falling off completely. As the disease progresses, the fungi will eventually reach the fruit and alter the natural color to a yellowish hue. Often, the plant dies before reaching its mature stage [4]. At this point, the fungus invades the plant's parenchymatous tissue, and it will eventually reach the surface of the dead tissue, where it can sporulate abundantly. The resulting spores can then be used as new inoculum for further spread of the fungus [11].

Although much more well known for the aforementioned plant pathogenicity, Fusarium oxysporum has also been shown to be pathogenic to humans and animals. [2]. The diseases associated with Fusarium include:

  • Fungal keratitis - The fungal infection of the cornea that can infect the eyeball and causes abscesses to form on it. [5]
  • Onychomycosis - The fungal infection of the nail that can cause fingernails or toenails to thicken, discolor, disfigure, and split. [6]
  • Hyalohyphomycosis - A fungal infection of the skin that can result in an extreme rash or penetrate the dermis and cause infection or internal bleeding. [7]
F. oxysporum is also pathogenic to humans. A: Fungal keratitis [8]. B: Onychomycosis [9]. C: Hyalohyphomycosis [10]

References

[1] http://www-unix.oit.umass.edu/~psoil120/images/fusarium.jpg
[2] http://www.mycology.adelaide.edu.au/Fungal_Descriptions/Hyphomycetes_%28hyaline%29/Fusarium/
[3] http://platforms.inibap.org/xanthomonaswilt/index.php?option=com_content&view=article&id=74&Itemid=94&lang=english
[4] http://www.oisat.org/pests/diseases/fungal/fusarium_wilt.html
[5] http://medical-dictionary.thefreedictionary.com/mycotic+keratitis
[6] http://www.emedicinehealth.com/onychomycosis/article_em.htm
[7] http://www.mycology.adelaide.edu.au/Mycoses/Opportunistic/Hyalohyphomycosis/
[8] http://www.uveitis.org/medical/articles/case/fungal_keratitis.html
[9] http://www.myfootshop.com/detail.asp?Condition=Onychomycosis
[10] http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2800%2902774-4/fulltext
[11] http://www.extento.hawaii.edu/kbase/crop/type/f_oxys.htm
[12] http://www.cabi.org/dmpd/default.aspx?site=165&page=4050&LoadModule=Review&ReviewID=170522
[13] http://sciweb.nybg.org/science2/hcol/fusarium3.asp
[14]

Author

Page authored by Andrew Smith and Andrew Smedley, students of Prof. Jay Lennon at Michigan State University.

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