First report of Verticillium dahliae causing verticillium wilt of Solanum aethiopicum in Italy

Solanum aethiopicum (African eggplant) is a very important vegetable throughout tropical Africa, especially in the less humid regions. It is also cultivated in some areas of southern Italy. In the last summer, a wilt disease of African eggplant was observed at one location in the Basilicata region (southern Italy). The most characteristic symptoms included yellowing, stunting, gradual wilting and brownish discoloration of vascular tissues. To elucidate the etiology of the disease, detection and identification of the causal agent(s) using both traditional and polymerase chain reaction (PCR)-based methods were attempted. Verticillium dahliae was consistently identified on the basis of its morphological features according to the description of Smith (1965), when cultured on potato dextrose agar (PDA) from small pieces of petiole and stem tissues taken from diseased plants. With PCR assays, using the primer pair ITS5/ITS4 (White et al., 1990), which are directed to fungal nuclear ribosomal DNA (rDNA) repeat sequences, an amplification product of approximately 560 bp was obtained using total DNA extracted from wilt affected-African eggplant tissues, as well as from fresh mycelium of the corresponding pure culture-maintained isolate. No PCR products were obtained with total DNA from asymptomatic African eggplants. Sequence analysis of the ITS5/ITS4 amplicons revealed that V. dahliae-infected African eggplant isolate (GenBank accession no. AJ970308) is identical to a Greek strain of V. dahliae (GenBank accession no. AF104926).

To fulfil Koch's postulates, ten healthy African eggplant seedlings were experimentally inoculated by dipping their trimmed roots in a single-conidial suspension containing 1.5 x 10⁶ CFU per ml and obtained from 10-day-old colonies of the V. dahliae-infected African eggplant pure culture-maintained isolate. All inoculated plants showed symptoms identical to those of naturally infected plants. V. dahliae was consistently reisolated from inoculated plants. This appears to be the first report of African eggplant infection by V. dahliae.