The soil-borne ascomycete Fusarium oxysporum is a pathogenic fungus common in soils around the world, and the cause of fusarium wilt, a deadly vascular wilting syndrome in a large variety of plant species. Of particularly urgent threat currently is the Fusarium oxysporum f. sp. cubense; the “form” of this fungus that causes wilting disease, called Panama Disease, in bananas (although studies show that this form is composed of several divergent, polyphyletic lineages; O’Donnell et al. 1998).
As this fungus does not respond to fungicides nor is it effectively manageable by other treatments, this pathogen became the conduit for one of the most destructive plant diseases in history when it spread throughout the world (with the exception of a few South Pacific Islands) in the 1950s, devastating plantations of Gros Michele banana, the almost exclusively-farmed banana cultivar at that time.The banana industry recovered only by converting to the production of Cavendash bananas, a generally F. oxysporum-resistant strain, as a substitute to Gros Michele (Butler 2013; IITA Press Release 2013; Plant Health Australia 2013; García-Bastidas et al. 2014; Wikipedia 2014b).
Banana plantations are now again seriously threatened, as the Cavendash is susceptible to a new variant of F. oxysporum f. sp. cubense termed Tropical Race 4 (Foc TR4).First identified in Asia in 1992, it subsequently spread to the Philippines and to Northern Australia.In 2013 TR4 was identified in Jordan and Mozambique, creating intense concern for its inevitable spread into banana producing countries in Africa and South America.Hygiene to reduce the spread of the fungus and transgenic techniques to introduce resistance genes into Cavendash bananas are tools researchers hope will save the industry this time (Butler 2013; IITA Press Release 2013; Plant Health Australia 2013; García-Bastidas et al. 2014; Wikipedia 2014b).
Fusarium oxysporum attacks its host by entering through the root.It grows in the plant xylem, eventually blocking the vascular system.This prevents transport of water and nutrients to the rest of the host, causing wilting, discoloration, and ultimately death of the plant (Gonsalves and Ferreira, 1993; Wikipedia 2014a).The leaves on an infected banana plant remain erect for 1 to 2 weeks as they start yellowing, then collapse at the leaf stalk so they hang down at the pseudostem and wither (Infonet Biovision 2011; Ploetz 2000).
Fusarium oxysporum Schlecht. as emended by Snyder and Hansen [1] comprises all the species, varieties and forms recognized by Wollenweber and Reinking [2] 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 [3][4], more recent work indicates this taxon is actually a genetically heterogeneous polytypic morphospecies [5][6] whose strains represent some of the most abundant and widespread microbes of the global soil microflora [7], 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 [8]. F. oxysporum strains are ubiquitous soil inhabitants that have the ability to exist as saprophytes, and degrade lignin [9][10] and complex carbohydrates [11][12][13] associated with soil debris. They are also pervasive plant endophytes that can colonize plant roots [14][15] and may even protect plants or be the basis of disease suppression [16][17.] 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.
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 [18] to humans [19], 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 speciales 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. As a category, forma specialis is mentioned in, but not regulated by, the International Code of Botanical Nomenclature and sometimes it has been inconsistently applied. Exhaustive host range studies also have been conducted for relatively few formae speciales or F. oxysporum[20]. 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).
The soil-borne ascomycete Fusarium oxysporum is a pathogenic fungus common in soils around the world, and the cause of fusarium wilt, a deadly vascular wilting syndrome in plants. Fusarium oxysporum comprises over 120 known strains or “special forms” (formae speciales; f. sp.), each of which is specific to a unique plant host in which it causes disease.Collectively, these F. oxysporum strains infect and kill a large host range including many commercially harvested crops such as species in the Solenaceae family (tomatoes, peppers, potatoes, eggplant), watermelon, lettuce, legumes, beets, basil, strawberries, chrysanthemum, sugarcane, bananas, and multiple other species. Fusarium oxysporum spores survive dormant in soil sometimes for 30 years, are easily spread in water, on machinery and seeds, and can hide in the rhizomes or vegetative cuttings of infected plants, showing no symptoms until transmitted to other individuals; all these are qualities that make this fungus an important and potentially devastating agricultural pest (Gonsalves and Ferreira 1993; Miller et al. 1996; New York Botanical Garden 2003; Wikipedia 2014a,b).
Of particular urgent threat currently is the Fusarium oxysporum f. sp. cubense; the special form specific to bananas, which causes Panama disease deadly to banana plants.Cavendash bananas, the strain which compose 85% of world banana exports, are generally F. oxysporum-resistant, however fall susceptible to a new variant of F. oxysporum f.sp. cubense, termed Tropical Race 4 (Foc TR4).FocTR4 was first identified in Asia in 1992, infecting the Philippines and Northern Australia shortly thereafter.In 2013 Jordan and Mozambique reported TR4 infected crops creating intense concern for its inevitable spread into banana producing countries in Africa and South America.Hygiene to reduce the spread of the fungus and transgenic techniques to introduce resistance genes into Cavendash bananas are tools researchers hope will save the industry (Butler 2013; IITA Press Release 2013; Plant Health Australia 2013; García-Bastidas et al. 2014; Wikipedia 2014c).
Fusarium oxysporum attacks its host by entering through the root.It grows in the plant xylem, eventually blocking the vascular system.This prevents transport of water and nutrients to the rest of the host, causing wilting, discoloration, and ultimately death of the plant (Gonsalves and Ferreira, 1993; Wikipedia 2014a).
In addition to having well-studied pathogenic activity in plants, the broad host range of Fusarium oxysporum extends outside plant kingdom, into Animalia.It is an emerging opportunistic human pathogen, reported as one of the most common agents causing invasive fungal infections in immunocompromised patients; as F. oxysporum is resistant to most available antifungal drugs, these infections are serious and frequently fatal in mammals.Scientists have proposed developing F. oxysporum as a universal model for understanding fungal virulence (Ortoneda et al. 2003).
Fusarium oxysporum (Schlecht as emended by Snyder and Hansen),[1] an ascomycete fungus, comprises all the species, varieties and forms recognized by Wollenweber and Reinking[2] within an infrageneric grouping called section Elegans. It is part of the family Nectriaceae.
Although their predominant role in native soils may be as harmless or even beneficial plant endophytes or soil saprophytes, many strains within the F. oxysporum complex are soil borne pathogens of plants, especially in agricultural settings.
While the species, as defined by Snyder and Hansen, has been widely accepted for more than 50 years,[3][4] more recent work indicates this taxon is actually a genetically heterogeneous polytypic morphospecies,[5][6] whose strains represent some of the most abundant and widespread microbes of the global soil microflora.[7]
The Fot1 family of transposable elements was first discovered by Daboussi et al., 1992 in several formae speciales[8][9] and Davière et al., 2001 and Langin et al., 2003 have since found them in most strains at copy numbers as high as 100.[8]
These diverse and adaptable fungi have been found in soils ranging from the Sonoran Desert, to tropical and temperate forest, grasslands and soils of the tundra.[10] F. oxysporum strains are ubiquitous soil inhabitants that have the ability to exist as saprophytes, and degrade lignin[11][12] and complex carbohydrates[13][14][1] associated with soil debris. They are pervasive plant endophytes that can colonize plant roots[15][16] and may even protect plants or form the basis of disease suppression.[17][18]
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 descended from a common ancestor.[19] However, results from research conducted on Fusarium oxysporum f. sp. cubense 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 across 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 were 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.[20]
Presented with the wide-ranging occurrence of F. oxysporum strains that are nonpathogenic, it is reasonable to conclude 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 exploit this ability and hopefully gain an advantage over fungi that are restricted to the cortex.
The progression of a fungus into vascular tissue may elicit an immediate host response, successfully restricting the invader; or an otherwise ineffective or delayed response, reducing the vital water-conducting capacity and induce wilting.[21] On the other hand, the plant might be able to tolerate limited growth of the fungus within xylem vessels, preceded by an endophytic association.[22] In this case, any further changes in the host or parasite could disturb the relationship, in a way that fungal activities or a host response would result in the generation of disease symptoms.
Pathogenic strains of F. oxysporum have been studied for more than 100 years. The host range of these fungi is broad and includes animals, ranging from arthropods[23] to humans,[24] 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 in 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.[25] For more information on Fusarium oxysporum as a plant pathogen, see Fusarium wilt and Koa wilt.
Different strains of F. oxysporum have been used for the purpose of producing nanomaterials (especially Silver nanoparticles).
In 2000, the government of Colombia proposed dispersing strains of Crivellia and Fusarium oxysporum, also known as Agent Green, as a biological weapon to forcibly eradicate coca and other illegal crops.[26] The weaponized strains were developed by the US government, who originally conditioned their approval of Plan Colombia on the use of this weapon, but ultimately withdrew the condition.[27] In February 2001, the EU Parliament issued a declaration specifically against the use of these biological agents in warfare.[27]
The fungus has the ability to dissolve gold, then precipitate it onto its surface, encrusting itself with gold. This phenomenon was first observed in Boddington, West Australia.[28] As a result of this discovery, F. oxysporum is currently being evaluated as a possible way to help detect hidden underground gold reserves.[29] It also is used to manufacture gold nanoparticles.[30]
Fusarium oxysporum (Schlecht as emended by Snyder and Hansen), an ascomycete fungus, comprises all the species, varieties and forms recognized by Wollenweber and Reinking within an infrageneric grouping called section Elegans. It is part of the family Nectriaceae.
Although their predominant role in native soils may be as harmless or even beneficial plant endophytes or soil saprophytes, many strains within the F. oxysporum complex are soil borne pathogens of plants, especially in agricultural settings.