Basil (Ocimum basilicum), a new host of Pepino mosaic virus

Pepino mosaic virus (PepMV), a member of the genus Potexvirus, was first described in 1980 on pepino (Solanum muricatum) and was later isolated from different wild species of the genus Solanum (formerly Lycopersicon) (Soler et al., 2002). PepMV has been reported in several European countries and in North America, causing disease in tomato. In July 2008, plants of basil (Ocimum basilicum) showing interveinal chlorosis on young leaves (Fig. 1) were observed in three greenhouses in Sicily, in the area where tomato plants were found to be infected by PepMV in 2005 (Davino et al., 2006).

The disease was transmitted mechanically to Nicotiana benthamiana, producing chlorotic spots and leaf deformation. Electron microscopy of negatively-stained preparations from symptomatic basil and N. benthamiana leaves revealed the presence of flexuous, filamentous virus particles, typical of potexviruses. Leaves from 100 plants with or without symptoms were analysed by double-antibody sandwich (DAS) ELISA using a polyclonal antibody to PepMV (Loewe Biochemica, Germany). The presence of the symptoms was correlated with positive ELISA results. Total RNA was extracted from the same samples using an RNeasy Plant Mini Kit (Qiagen, Hilden, Germany) and analysed by RT-PCR using the PepMV-specific primers PepMV-TGB-F and PepMV-UTR-R (Mumford and Metcalfe, 2001). The 840bp RT-PCR product was sequenced in both directions and the sequence deposited in GenBank (Accession No. EU888637). The sequence had 99% sequence identity with an isolate of PepMV found in Sicily in 2005 (DQ517884). This is the first report of PepMV infecting basil. Although the disease does not appear too severe on basil, the species is frequently cultivated next to tomatoes and PepMV is transmitted mechanically easily; therefore basil may act as a virus reservoir.