The infection process of Fusarium oxysporum f.sp vasinfectum in Australian cotton

The infection process of two commercial Australian cotton varieties differing in susceptibility to Fusarium oxysporum f. sp. vasinfectum (Fov) was investigated. There were no differences in the early stages of infection between the host cultivars. Conidia germinated and developed an extensive hyphal net around the root. Penetration of epidermal cells was most common in the root hair zone, causing colonisation of the root hairs and epidermal cells before hyphae invaded the cortex by both intra- and intercellular growth. Colonisation of the stele of the moderately resistant variety Sicot 189 was arrested within 3 days, while growth in the highly susceptible Siokra 1-4 continued for 5 days. The restriction of Fov in the xylem of Sicot 189 indicates a differential activation of defence responses in this cultivar that corresponds with field resistance.