Fusarium oxysporum

Fusarium oxysporum, also referred to as Agent Green, is a fungus that causes Fusarium wilt disease in more than a hundred species of plants. It does so by colonizing the water-conducting vessels (xylem) of the plant. As a result of this blockage and breakdown of xylem, symptoms appear in plants such as leaf wilting, yellowing and eventually plant death.

Interest in Fusarium oxysporum as a pesticide was first raised after the discovery in the 1960s that it was the causative agent in the destruction of the Hawaiian coca population.

The United States government was involved in a controversial program to use Fusarium oxysporum for the eradication of coca in Colombia and other Andean countries, but these plans were cancelled by president Bill Clinton who was concerned that the unilateral use of a biological agent would be perceived by the rest of the world as biological warfare. The Andean nation have since banned its use throughout the region. Use of biological agents to kill crops is potentially illegal under the Biological Weapons Convention.

Different special forms (f.sp.) of F. oxysporum

• Fusarium oxysporum f.sp. albedinis
• Fusarium oxysporum f.sp. asparagi
• Fusarium oxysporum f.sp. batatas
• Fusarium oxysporum f.sp. betae
• Fusarium oxysporum f.sp. cannabis
• Fusarium oxysporum f.sp. cepae
• Fusarium oxysporum f.sp. ciceris
• Fusarium oxysporum f.sp. citri
• Fusarium oxysporum f.sp. coffea
• Fusarium oxysporum f.sp. cubense
• Fusarium oxysporum f.sp. cyclaminis
• Fusarium oxysporum f.sp. herbemontis
• Fusarium oxysporum f.sp. dianthi
• Fusarium oxysporum f.sp. lentis
• Fusarium oxysporum f.sp. lini
• Fusarium oxysporum f.sp. lycopersici
• Fusarium oxysporum f.sp. medicaginis
• Fusarium oxysporum f.sp. melonis
• Fusarium oxysporum f.sp. nicotianae
• Fusarium oxysporum f.sp. niveum
• Fusarium oxysporum f.sp. passiflorae
• Fusarium oxysporum f.sp. phaseoli
• Fusarium oxysporum f.sp. pisi
• Fusarium oxysporum f.sp. radicis-lycopersici
• Fusarium oxysporum f.sp. ricini
• Fusarium oxysporum f.sp. tulipae
• Fusarium oxysporum f.sp. vasinfectum

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Countermeasures

A number of recent patents specifically describe effective treatments of Fusarium oxysporum, reflecting its widespread importance as an agricultural pest.

• US 5,614,188: two strains of Bacillus in a composition of chitin and lime used to fight Fusarium in the soil.

• US 2004/136964 A1: Trichoderma asperellum mixed into container media (such as peat).

• US 4,714,614: a strain of Pseudomonas putida in combination with an iron chelating agent (such as EDTA).

• US 4988586: any of six types of bacteria that degrade fusaric acid, a toxin that damages plants and furthers infection.

• US 6100449 and WO 1996/032007 A1: a small genomic region (I2C) conferring resistance in transgenic tomatoes.

• US 2003/131376 A1: use of transgenic plants expressing enzymes capable of destroying Fusarium cell walls.

• US 4006265: spraying of crops with hydrogen peroxide to reduce the effect of contamination by Fusarium toxins.

• WO 2005/074687 A1: cure of infected plants by spraying with natamycin or other polyene antibiotics.

See also

• Mycoherbicide

Panama disease

Panama disease, also known as Fusarium wilt, is a banana plant disease caused by the fungus Fusarium oxysporum. The fungus attacks the roots of the banana plant. The disease is resistant to fungicide and, so, cannot be controlled chemically.

History

Gros Michel or 'Big Mike' was an early export cultivar of banana. This cultivar was wiped out by Panama disease in the 1950s. The disease first appeared in Suriname, then made its way to the Caribbean, and by the 1920s, to Honduras, the world's largest producer of bananas at the time. Although there are many banana cultivars, Gros Michel was especially suitable for export to non-tropical nations. A search for a substitute located the Vietnamese Cavendish cultivar which is resistant to the disease. However, more care is required for shipping the Cavendish banana and its quality compared to Gros Michel is debated.

Recently, a new strain called 'tropical race four Panama disease' has begun to attack Cavendish banana plants in south Asia. Given the high volume of modern international trade, banana producers expect this strain to spread through Africa and into South America and the Caribbean.

Plant breeders and geneticists are trying to develop new cultivars that are resistant to this new strain of Panama disease. Unfortunately, such efforts are progressing slowly because the banana cultivars selected for human consumption are seedless and reproduce asexually which decreases genetic variation and makes breeding difficult.

Resources

• International Network for the Improvement of Banana and Plantain (INIBAP)