First Report of Fusarium Wilt on Hebe sp. in Italy and Europe

Hebe (showy speedwell), an increasingly important crop in the Riviera Ligure (northern Italy), is cultivated in greenhouses and open fields. During summer 1999, a serious wilt of hybrids (Hebe speciosa × H. franciscana cvs. Paula, Linda, and Heidi) grown in plastic pots (14 to 16 cm diameter) in a peat/pomix/clay (70:20:10, vol/vol) substrate was observed. Symptoms appeared on one side of the plant or on a single branch. Affected plants showed only slight yellowing before wilting. Wilting progressed acropetally. Eventually, affected plants were completely wilted, and stems showed dark blue-black necrosis, often covered by mycelia. An intense brown discoloration of the vascular system was evident shortly after the appearance of the first symptoms. In some cases, whole plants suddenly wilted. Infected plants generally were stunted and eventually died. Fusarium oxysporum was isolated consistently from diseased plants on Komada's (1) Fusarium-selective medium. One single-spore isolate of F. oxysporum, freshly isolated from wilted plants, was used for artificial inoculation of healthy plants to complete Koch's postulates. Rooted cuttings were transplanted in soil artificially infested with 1 × 10³ CFU/ml of soil. Inoculation was performed on 20 plants belonging to two cultivars (Paula and Heidi). Noninoculated plants of each cultivar served as controls. Plants were maintained in a glasshouse at 25°C. The first symptoms developed 20 days after transplanting in infested soil. Symptoms resulting from artificial inoculation were similar to those observed on naturally infected plants. F. oxysporum was consistently reisolated from inoculated plants. Fusarium wilt of Hebe is favored by temperatures higher than 20°C. Symptoms did not develop on inoculated plants maintained in the open field during the month of October nor in the greenhouse at temperatures lower than 18°C. This is the first report of Fusarium wilt on Hebe sp. in Italy and Europe. A similar wilt on H. buxifolia and other Hebe spp. has been reported by Raabe in the United States (2,3). References: (1) H. Komada. Rev. Plant Prot. Res 8:114, 1975. (2) R. D. Raabe. Phytopathology 47:532, 1957. (3) R. D. Raabe. Plant Dis. 69:450, 1985.