First report of Verticillium wilt of artichoke caused by Verticillium dahliae in Tunisia

In a survey of Verticillium wilt in Chott Mariem region, situated in the eastern part of central Tunisia, wilt symptoms were observed on field-grown artichoke (Cynara scolymus) during the spring of 2006. Diseased plants showed stunting, yellowing, wilting and desiccation of the leaves (Fig. 1), with extensive vascular browning in the stem (Fig. 2). Discoloration was observed in the vascular tissue of roots, crown and leaves. Diseased plants produced a few smaller, deformed buds and, in severe cases, buds were discoloured with dried outer bracts. A high proportion of infected plants were seen in most fields examined near harvest. Isolates from diseased plants were identified as Verticillium dahliae on the basis of microsclerotium production (Hawksworth & Talboys, 1970).

Pathogenicity tests were carried out using root-dip inoculation. Three V. dahliae isolates were tested on artichoke offshoots which were submerged for 30 min in a conidial suspension (1x10⁷ conidia per ml), while control plants were similarly submerged in sterile tap water. Seedlings were transplanted into pots containing a sterile 2:1 mixture of peat/perlite (v/v) and maintained in a growth chamber at 23±2°C. V. dahliae isolates were pathogenic to artichoke plants. Symptoms developed by 40 days after inoculation and consisted of chlorosis, wilting and necrosis of basal leaves which progressed upward on the plant to reach the newly formed ones. No symptoms developed in uninoculated controls. In other inoculation studies, artichoke isolates were able to cause moderate to severe levels of disease in race 1- susceptible (cv Ventura) and race 1- resistant (cv. Rio Grande and cv. Colibri) tomato plants and were typed as race 2. Likewise, these isolates were able to cause typical Verticillium symptoms when inoculated to potato (cv. Spunta), eggplant (cv. Bonica) and melon (cv. Ananas d'Amérique) seedlings. V. dahliae was successfully re-isolated from the stems of the inoculated plants.

The appearance of V. dahliae in artichoke fields in Tunisia poses a threat to this and other economically important crops (potato, tomato, melon and eggplant), which are all Verticillium- susceptible. These crops are usually grown in the same fields as are used for artichokes but no rotations with Verticillium-resistant crops are used. The disease has been previously reported in Italy, France, Greece (Jimenez Diaz et al., 2006) and California (Bhat & Subbarao, 1999) but this is the first report from Tunisia.