Oxysporum

Oxysporum is a species epithet used in several fungal taxa, most notably Fusarium oxysporum, a widespread soil-borne plant pathogen belonging to the phylum Ascomycota. Fusarium oxysporum is a species complex comprising many physiologically diverse isolates, classified into numerous formae speciales (ff. sp.) that determine host range.

Biology and ecology: The fungus grows as hyphae and forms chlamydospores that enable long-term survival in soil. It infects plants primarily through the roots and colonizes xylem vessels, causing vascular wilt. Infected plants exhibit wilting, yellowing, stunting, and sometimes browning of vascular tissue in the stem; the disease can progress rapidly under warm, moist conditions. The pathogen persists in soil for years and can spread with water, infested soil, or contaminated tools. F. oxysporum has a cosmopolitan distribution and a broad host range, with different ff. sp. specialized to crops such as tomato (f. sp. lycopersici), banana (f. sp. cubense), and various cucurbits and ornamentals.

Diagnosis and management: Identification combines symptom observation with isolation and molecular assays targeting housekeeping genes or pathogenicity-related genes (including SIX genes) to infer formae speciales. Not all isolates are pathogenic; some nonpathogenic strains exist and are studied for biocontrol and endophytic associations. Control is challenging; strategies include crop rotation with non-hosts, use of resistant cultivars, soil solarization, sanitation, and biological control agents. Quarantine and sanitation are important to limit spread.

Impact and significance: F. oxysporum is a globally important plant pathogen, responsible for substantial crop losses. Notably, the tropical race 4 of the banana-infecting form has threatened Cavendish cultivars in multiple regions.