Sources of resistance in wild Solanum germplasm (section Lycopersicon) to parietaria mottle virus, an emerging virus in the Mediterranean basin

Parietaria mottle virus (PMoV) is considered an emerging virus in many countries of the Mediterranean basin. Outbreaks of tomato necrotic disease caused by the tomato strain PMoV-T have been recorded in Italy, France, Spain, and Greece. No resistant or tolerant tomato cultivars are available and no cases of resistance have been reported in the section Lycopersicon of the Solanum genus so far. Therefore, wild relatives of tomato were evaluated to identify potential sources of resistance to PMoV infection. In all, 16 germplasm accessions from six wild Solanum spp. of the section Lycopersicon, along with susceptible near-isogenic tomato lines (Monalbo, Momor, and Mospomorist), were evaluated for resistance against two different PMoV-T strains, TI1 (from Italy) and FR1 (from France), under greenhouse conditions using mechanical inoculations. Local and systemic virus infections were determined by enzyme-linked immunosorbent assay (ELISA) 15 and 30 days after mechanical inoculation and confirmed by dot-blot hybridization of viral RNA with a PMoV-specific digoxigenin-labelled riboprobe. No local or systemic symptoms were observed in three accessions of S. peruvianum and one accession of S. corneliomuelleri. Moreover, the virus was never detected in the inoculated and upper noninoculated leaves of these accessions, either with ELISA or the specific riboprobe. The accession of S. lycopersicum var. cerasiformae was resistant only to the TI1 strain. This is the first description of sources of extreme resistance to PMoV in the section Lycopersicon of the Solanum genus.