First report of fusarium wilt of cucumber caused by Fusarium oxysporum in Spain

In 2000, cucumber (Cucumis sativus L. cv. Albatros) in several commercial greenhouses in south-eastern Spain (Almería) exhibited symptoms of wilt, yellowing, and necrotic streaks on the stems.

Internal, vascular discoloration in affected plants extended from the base of the stem upward. Initial observations were reminiscent of Fusarium wilt disease of cucumber, caused by Fusarium oxysporum Schlechtend:Fr. f. sp. cucumerinum J.H. Owen, as described by Owen (1955).

Pure colonies of fungi were isolated from surface-disinfested (with flame) stem segments, cut at 0.5 m above the hypocotyl, on potato dextrose agar (PDA) medium. Isolates were identified as Fusarium oxysporum due to their production of typical macroconidia with foot-shaped basal cells, microconidia borne in false heads only on monophialides, and chlamydospores. To confirm pathogenicity, eight isolates (1-week-old cultures grown on PDA) were used to root-dip inoculate (1 x 10⁶ conidia per ml) 1-week-old seedlings of cucumber cvs. Nevada and Albatros. Seedlings were then transplanted into pots containing vermiculite growth medium and placed in a greenhouse. Of the tested isolates, 87.5% were pathogenic, causing wilt symptoms or death in 60 to 100% of dip-inoculated plants, from which F. oxysporum was consistently reisolated. Symptoms observed in inoculated plants were similar to that observed in cucumber plants in commercial greenhouses. This is the first report of F. oxysporum causing Fusarium wilt of cucumber in Spain.