Fusarium oxysporum

The ascomycete fungus Fusarium oxysporum  Fusarium Oxysporum  Schlecht.as emended by Snyder and Hansen comprises all the species, varieties and forms recognized by Wollenweber and Reinking within an infrageneric grouping called section Elegans. While the species, as defined by Snyder and Hansen, has been widely accepted for more than 50 years, more recent work indicates this taxon is actually a genetically heterogeneous polytypic morphospecies whose strains represent some of the most abundant and widespread microbes of the global soil microflora, although this last statement has not been proven or supported by actual data. These remarkably diverse and adaptable fungi have been found in soils ranging from the Sonoran Desert, to tropical and temperate forests, grasslands and soils of the tundra. F. oxysporum strains are ubiquitous soil inhabitants that have the ability to exist as saprophytes, and degrade lignin and complex carbohydrates associated with soil debris. They are also pervasive plant endophytes that can colonize plant roots and may even protect plants or be the basis of disease suppression. Although the predominant role of these fungi in native soils may be as harmless or even beneficial plant endophytes or soil saprophytes, many strains within the F. oxysporum complex are pathogenic to plants, especially in agricultural settings.

Contents

• Fusarium Wilt
• Formae speciales special forms
• Patents relating to the management of Fusarium oxysporum
• References

Because the hosts of a given forma specialis usually are closely related, many have assumed that members of a forma specialis are also closely related and have descended from common ancestor. However, results from recent research conducted on *Fusarium oxysporum f. sp. cubense have forced scientists to question these assumptions. Researchers used anonymous, single-copy restriction fragment length polymorphsims (RFLPs) to identify 10 clonal lineages from a collection of F. oxysporum f.sp. cubense from all over the world. These results showed that pathogens of banana causing Panama disease could be as closely related to other host's pathogens, such as melon or tomato, as they are to each other. Exceptional amounts of genetic diversity within F. oxysporum f.sp. cubense also have been deduced from the high level of chromosomal polymorphisms found among strains, random amplified polymorphic DNA fingerprints, and from the number and geographic distribution of vegetative compatibility groups.

Presented with the wide-ranging occurrence of F. oxysporum strains that are nonpathogenic, it is reasonable to expect that certain pathogenic forms were descended from originally nonpathogenic ancestors. Given the association of these fungi with plant roots, a form that is able to grow beyond the cortex and into the xylem could quickly take advantage of this ability and hopefully gain an advantage over those fungi that are restricted to the cortex. The progression of a fungus into the vascular tissue may elicit a response from the host immediately, successfully restricting the invader; or an otherwise ineffective or delayed response, reducing the vital water-conducting capacity to induce wilting. On the other hand, the plant might be able to tolerate limited growth of the fungus within xylem vessels, preceded by an endophytic association. In this case, any further changes in the host or parasite could disturb the relationship, in a way that fungal activities or a response of the host would result in the generation of certain disease symptoms.

Pathogenic strains of F. oxysporum have been studied for more than 100 years. The host range of these fungi is extremely broad, and includes animals, ranging from arthropods to humans, as well as plants, including a range of both gymnosperms and angiosperms. While collectively, plant pathogenic F. oxysporum strains have a broad host range, individual isolates usually cause disease only on a narrow range of plant species. This observation has led to the idea of "special form" or forma specialis in F. oxysporum. Formae speciales have been defined as "...an informal rank in Classification.....used for parasitic fungi characterized from a physiological standpoint (e.g. by the ability to cause disease in particular hosts) but scarcely or not at all from a morphological standpoint." Exhaustive host range studies have been conducted for relatively few formae speciales of F. oxysporum. For more information on Fusarium oxysporum as a plant pathogen, see Fusarium wilt.

Different strains of F. oxysporum have been used in the purpose of producing nanomaterials (especially Silver nanoparticles).