First report of Verticillium dahliae on Hebe x franciscana in Italy

In 2002, several plants of Hebe × franciscana cv. Variegata, grown in a public garden near Rome, Italy, showed wilting and severe stunting. Symptoms on affected plant started with yellowing and browning of the lower leaves, followed by wilting of one or more branches (Fig. 1). Stunting and death of plants were sometimes observed. Longitudinal sections of stems showed discolouration of vascular tissues extending from the base upwards (Fig. 2).

Isolations were attempted directly from discoloured vascular tissues on potato dextrose agarose (PDA). Fungal colonies were consistently obtained and identified as Verticillium dahliae on the basis of the morphology of conidia, conidiophores and microsclerotia. To confirm pathogenicity, a single-spore V. dahliae isolate from Hebe, grown for 20 days in Petri dishes on PDA, was homogenized in a blender with 100 ml of sterile water and adjusted to a final concentration of 1.5x10⁶ CFU per ml. Hebe × franciscana rooted cuttings (15 in total) were dipped for 5 min into the inoculum, then singly transplanted in plastic pots containing autoclaved soil and maintained in a greenhouse at 20± 3°C until symptoms appeared. An equal number of plants (controls) were left uninoculated. After 30 days, symptoms comparable with those present in naturally affected plants were observed on all the inoculated plants (Fig 3). V. dahliae was consistently isolated from symptomatic tissues taken from inoculated plants.

Several species of Hebe are gaining the interest of the flower industry in Italy for growing in the open air and in the greenhouse. Recently, a wilt of Hebe caused by Fusarium oxysporum was reported for the first time in Italy and Europe (Garibaldi et al., 2000). Verticillium wilt is a common problem for several woody and herbaceous ornamental plant species in Italy and worldwide (Pirone, 1978). An unidentified Verticillium sp. has been reported on Hebe sp. in the USA (Pegg & Brady, 2002) but to the best of our knowledge this is the first report of the disease on this host in Italy or anywhere outside the USA.