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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).