First report of Alternaria petroselini on fennel in Italy

During 2007, fennel (Foeniculum vulgare) plants grown in Metaponto (Matera, Italy) were observed with black depressed lesions on the basal leaves (Fig. 1). More than 50% of the inspected fields showed symptoms with an incidence ranging from 30 to 100%. Isolations were carried out from infected leaves on potato dextrose agar (PDA) amended with streptomycin sulphate and ampicillin (100 µg/ml each). An Alternaria sp. was consistently isolated, then transferred to potato carrot agar (PCA) under near-UV lights for morphological characterisation. Two kinds of conidia were obtained from dark brown colonies: sub spherical to oval (33.0 ± 5.6 x 18.0 ± 3.4 μm) and elongated ellipsoidal (52.8 ± 6.1 x 22 ± 2.7 μm) (Fig. 2). Microsclerotia were observed beneath the agar surface, and there was no pigmentation. Radial growth of one isolate (ISPaVe ER 1461) on PCA at 22° C after eight days was higher (70.5 mm) compared to that of a known A. radicina isolate CBS 112003 (41.1 mm). No products were obtained after DNA amplification of ISPaVe ER 1461 with specific primers designed for A. radicina (Pryor & Gilbertson, 2001). On the basis of this data, the fungus was identified as Alternaria petroselini (Neergard) Simmons (Pryor & Gilbertson, 2002). The ITS region of the isolate ISPaVe ER 1461 was amplified using the universal primers ITS5 and ITS4 (White et al., 1990). The sequence was deposited in GenBank with Accession No. FJ623264. A BLAST homology search of the sequences showed 100% identity with GenBank sequences corresponding to Alternaria petroselini isolates EU807868 and EU781948.

A pathogenicity test was conducted on adult fennel plants by spraying a conidial suspension of the fungus (10⁵ conidia/ml) to runoff. Control plants were sprayed with sterile deionised water. After inoculation, plants were covered with plastic bags for 48 h in a greenhouse at 25-27°C, then uncovered and kept wet until symptoms appeared. One week after inoculation, small dark spots were observed, that soon developed into necrotic areas on the fennel stalks (Fig 3). Koch’s postulates were fulfilled by re-isolating the same fungus from infected stalks.

This species has been recently reported to cause seedling damping-off on fennel in the Netherlands (Pryor & Asma, 2007). This is the first report of A. petroselini on fennel in Italy. The disease causes a significant reduction in quality.