Spread of Tomato spotted wilt virus from an internal virus source by thrips species in Samsun, Turkey

The temporal and spatial distribution of Tomato spotted wilt virus (TSWV) was studied in a 2,085 m(2) tomato field with a total of 4,080 plants during 10 weeks from 5 July to 6 September in 2004. First infected plants were detected 4 weeks after the source plants were placed in the field and their number continued to increase by week 7. A total of 147 plants (3.6%) were recorded to be infected according to symptom occurrence and serological test by the end of the experiment. Thrips monitoring was carried out from May 25 to October 25 in the same year. Two thrips species, Frankliniella intonsa (Tryborn) and Thrips tabaci (Lindemann), were determined in the experimental area, with the latter one being the more prevalent (84.9%) species. There was a significant correlation (r = 0.988, P < 0.01) between the number of thrips species and the number of infected plants in the field. Majority of infected plants were not located near (0-10 m) an internal virus source within the experimental area, whereas 45.6% of the infected plants were located at a distance of 21-30 m. The number of infected plants at a distance of 21-25 m was significantly higher than at all other distances (P < 0.05). There was no gradual increase in the distances of TSWV-infected plants within 0-30 m as time progressed. The virus seems to be transmitted by vectors through primary infections and scattered within 30-m distance, but limited secondary infections seem likely to occur after this distance in the case of a small internal virus source.