Evaluation of Solanum germplasm for resistance to tomato spotted wilt virus

Tomato spotted wilt virus (TSWV) is one of the most damaging viruses affecting solanaceous crops, especially tomato and pepper. Recently, field infections have also been observed in eggplant (Solanum melongena) in southern Italy. To evaluate wild Solanum species useful for breeding purposes, twenty-two wild Solanum accessions and two eggplant varieties were tested for resistance to TSWV with the SOM-1 isolate from S. melongena. Plants were inoculated mechanically at the stage of two true leaves and checked weekly for symptoms development up to 40 days post inoculation (d.p.i.). TAS-ELISA with a cocktail of monoclonal antibodies (MAbs) against TSWV nucleocapsid (N), was used to detect TSWV in inoculated leaves and in the upper non inoculated leaves 15 and 30 d.p.i.. A TSWV-specific digoxigenin-labelled riboprobe was also used in dot-blot hybridisation assays to detect the virus. Two accessions gave the best results out of 22 tested. In fact, one accession of Solanum pseudocapsicum reacted with chlorotic local lesions of inoculated leaves and no systemic symptoms. Serological testing of apical leaves gave negative results, while dot-blot hybridisation revealed two plants with a latent infection out of 10 within the same accession. Interestingly, inoculated and non-inoculated leaves of an accession of Solanum linneanum remained symptomless up to 40 d.p.i.. ELISA was positive only when inoculated leaves were tested. These findings were confirmed by dot-blot hybridisation with the TSWV-specific riboprobe. The accession of Solanum linneanum tested may then represent a new potential source of resistance to TSWV useful for breeding programmes