Evaluation of commercial Lycopersicon esculentum hybrids for resistance to tomato spotted wilt tospovirus (TSWV) in Spain

The recent commercialization of tomato hybrids resistant to tomato spotted wilt tospovirus (TSWV) in Spain by different seed producer companies has reduced the economic losses caused by this virus. However, the presence of TSWV-infected plants or fruits showing peculiar ring spots in commercial fields planted with these hybrids have prompted this study. A comparative assay of mechanical inoculation and natural infection by thrips of TSWV provided different results. The assays carried out using different hybrids, supposedly resistant to TSWV, have shown that the presence of the SW-5 gene from cultivar 'Stevens' is the only effective source of resistance; although a low proportion of susceptible plants can be found in the seed lots. In some of them, the virus partially overcame this resistance, although no changes in infectivity of virus isolates has been detected; in other cases there is a typical infection of the virus by absence of SW-5 gene. However, its presence seems to be more important in the field assay of ring spots caused by TSWV on some tomato fruits produced by apparently healthy plants containing the SW-5 gene. The evidence presented here indicated that the probably the cause is the feeding of viruliferous thrips, which implies new epidemiological considerations because the time of infection and the economic losses with respect to infectious process of susceptible tomato crops are different and the control measures would need to be modified.