Viruses infecting tomato in València, Spain: occurrence, distribution and effect of seed origin.
Viral diseases are a serious limitation to the tomato crop in the region of València, Spain. A survey of tomato viruses in open field cultivation plots was made in the three provinces of this region. A total of 228 plots classified according to the origin of the seed (farmer seed plots or commercial seed plots) were surveyed, from which 1300 individual plants were sampled and tested for Cucumber mosaic virus (CMV), Pepino mosaic virus (PepMV), Parietaria mottle virus (PMoV), Potato virus Y (PVY), Tomato mosaic virus (ToMV), Tomato spotted wilt virus (TSWV) and for the tomato yellow leaf curl disease (TYLCD). Virus infection was detected in 58.9% of the plants sampled and in 86.0% of the plots surveyed. All these viruses were detected, and the most prevalent were ToMV and PVY (34.1% and 27.1% of infected plants, respectively), but PMoV and TYLCD were the less prevalent (1.2% and 1.3% of infected plants, respectively). Differences among provinces and seed origin were found for most of the viruses studied. In particular, both ToMV and PVY had a higher level of infection in plants from farmer seed plots than in commercial seed plots, which accounts for the higher percentage of virus-infected plants in the former (64.2%) when compared to the latter (49.1%). Single and multiple infections were found in 42.38% and 16.54% of the samples, respectively. The most common multiple infection was of ToMV, PVY or both. These results show that the percentage of infected plants and plots in open field cultivation is very high in this region and the origin of the seed is an important factor in the incidence of virus infection. In this respect, preventive measures, including virus-free seed, resistant cultivars and improved cultural practices, could reduce the incidence of virus infection.