Capparis spinosa - a new host for Sclerotium rolfsii

Caper (Capparis spinosa) is a small perennial shrub cultivated for the consumption of immature flower buds. In Italy it is grown on ca. 1000 ha in Sicily; mostly in the Eolie islands and Pantelleria. In June 2005, wilting was first observed in three fields, with up to 30% of plants in each field affected on between 1-5 branches (Fig. 1), with whitish mycelium and rotting tissue often present at the base of symptomatic shoots. During another survey in September, several plants with symptoms were observed in almost all the locations inspected. Isolations from infected tissues onto potato dextrose agar (PDA) amended with antibiotics, yielded colonies of a rapidly-growing, whitish mycelium with small round, brown sclerotia, allowing identification of the fungus as Sclerotium rolfsii (Fig. 2).

Pathogenicity of the isolate ISPaVe ER-1368 was tested using two inoculation methods: i) by placing a small plug (1.5 diam.) of the fungus, wrapped with Parafilm, near the collar region of healthy, two-year old caper plants; ii) by pouring 50 ml of a mycelial suspension (2 x 10³ CFU per ml) at the base of each plant. After eight days, yellowing of basal leaves, followed by wilting and drying of the young shoots was observed on plants inoculated by both methods (Fig. 3 and 4). Koch's postulates were satisfied by the reisolation of the fungus on PDA.

Several fungi attack caper worldwide (Ciferri, 1949; Kavak, 2004). To our knowledge, this is the first report of S. rolfsii on caper. S. rolfsii is a cosmopolitan pathogen of many cultivated crops and weeds (Mordue, 1974). Generally, Sicily and its Minor Islands are characterized by a hot and dry weather. In the last two years rainy springs and summers have been followed by hot weather; conditions favourable for the development of S. rolfsii. Control measures are difficult for diseases on perennial crops where sclerotia can persist in soil and crop residues for years. They include removal of crop debris, weed control, long crop rotation and the reduction of any stress factor during cultivation.