Paris daisy (Argyranthemum frutescens) is an economically important crop on the Riviera Ligure (Northern Italy), where approximately 10 million plants per year are produced for export. In September 1997, a serious wilt of plants (cv. Camilla) grown in plastic pots (14 to 18 cm in diameter) was observed. The leaves of the affected plants turned yellow unilaterally and eventually wilted. Both yellowing and wilting progressed acropetally. Eventually, affected plants were completely wilted and the stems showed dark blue-black necrosis. An intense brown discoloration of the vascular system was evident, particularly after yellowing of the foliage was visible. Fusarium oxysporum was consistantly isolated from diseased plants on Komada's medium (1). Two monoconidial isolates of F. oxysporum freshly isolated from A. frutescens wilted plants were used for artificial inoculation of healthy cv. Camilla plants in order to complete Koch's postulates. Rooted cuttings were inoculated by a root dip (for 30 s, with 5 × 107 CFU per ml) and by infesting soil (1 × 103 CFU per ml of soil). Inoculation was carried out on 20 plants belonging to five cultivars. Noninoculated plants of each cultivar served as control. Plants were maintained in a glasshouse at 22 to 23°C. Symptoms developed 13 to 14 days after and were similar to those observed on naturally infected plants. F. oxysporum was consistantly reisolated from artificially inoculated plants. Fusarium wilt of A. frutescens is favored by temperatures higher than 20°C. To our knowledge, this is the first report of Fusarium wilt on A. frutescens.
Reference: (1) H. Komada. Rev. Plant Prot. Res. 8:114, 1975.