Wilt of stock (Mattiola incana) caused by Fusarium oxysporum in the United Kingdom

In June 2003, a wilt disease occurred in Lincolnshire in a glasshouse crop of column stocks (Mattiola incana). Plants showed a one-sided wilt that progressed from the base upwards. Leaves subsequently became bleached, growth was stunted and plants died. Roots appeared healthy but the vascular tissue was stained dark brown. White fungal growth developed extensively on damp incubation of leaves and stems. Although stocks had been grown in the glasshouse for over 12 years, the disease had not been observed previously. A Fusarium species was consistently recovered, following surface sterilisation, from within stems and roots and from the fungal growth on leaves. Culture characteristics and morphology were typical of Fusarium oxysporum (Booth, 1971). Colonies on PDA produced a violet pigmentation in reverse and dark, purple sterile stromatic pustules. Ellipsoid microconidia, produced in slimy heads from short monophilaides on sucrose nutrient agar, were 2-5(-8) µm long; chlamydospores and 3-septate macroconidia were produced sparsely.

The roots of 10 plug plants (cv. Centum White) were dipped in a spore suspension (3x10⁶ conidia per ml) of the F. oxysporum isolated from the stocks and were then potted in soil-less compost. Another 10 plants were grown in compost admixed with bleached leaves taken from wilted plants (c. 10 g per pot). After 3 weeks, both sets of plants had wilted and collapsed and F. oxysporum was re-isolated. Control plants remained healthy.

The disease was subsequently confirmed in several other stocks crops in England, sometimes with over 80% losses. A fusarium wilt of stocks caused by F. oxysporum f. sp. mattioli has previously been described in Arizona and California (Baker, 1948). In England, F. oxysporum was consistently isolated from the vascular tissue of wilting stocks with brown vascular staining on a nursery in Kent in 1971. The problem reoccurred in 1975 and 1987 in the same glasshouse (JT Fletcher, pers. comm.). Baker (1948) demonstrated that the fungus was seed-borne, similar to many other F. oxysporum diseases. The inoculation tests reported here indicate that infection may also arise from crop debris incorporated into the soil.