Fusarium oxysporum

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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

Description and Significance

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

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.
In terms of life cycle, F. oxysporum has 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. [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
  

In general, the fungi manages to infect the vascular system of the plant, where it wreaks havoc. The outward signs of fusarium wilt is the plant's leaves turning yellow or brown, and then falling off. 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]

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]

Author

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

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