Transmission of Tomato Spotted Wilt Virus to Tomato Plants of Different Ages

Thrips (Thysanoptera: Thripidae) and mechanical transmissions of tomato spotted wilt virus (TSWV) to tomato (Lycopersicon esculentum Mill, cv. ‘Sunny Hybrid’) were investigated relative to plant age at the time of inoculation. In 1999, thrips and mechanical transmissions were compared between plants at 7, 14 and 28 d after germination under field exclusion cages. In 2000, thrips transmission was evaluated in plants at 7, 14, 21, 28, 35 and 42 d after germination, and mechanical transmission was evaluated in plants at 14, 21, 28, 35, 42 and 49 d after germination. Subsamples of thrips from flowers of TSWV-infected tomato used in 1999 transmission consisted of 59% Frankliniella occidentalis (Pergande), 34% F. tricici (Fitch), and subsamples of thrips collected from onion used in 2000 transmission consisted of 78% F. occidentalis and 19% F. fusca (Hinds). There was significant yield reduction resulting from early transmission of TSWV in the mechanical transmission test in 2000 (P= 0.008), but not in thrips transmission test in 2000 (P= 0.62). A reduction in the percent of TSWV-damaged fruit in late transmission was significant in the thrips transmission test (P = 0.04) but not in the mechanical transmission test (P= 0.25) in 2000. Lag time from virus transmission to symptom development or to a positive ELISA test was highly correlated to TSWV damaged fruit (P < 0.001 and P < 0.001, respectively) in the mechanical transmission test in 2000. The lag time of a positive ELISA in the thrips transmission test in 2000 correlated with the percentage of TSWV-damaged fruit (P = 0.009). In summary, early infection of TSWV to tomato plants resulted in lower yield and a higher percentage of TSWV-damaged fruits than late infection.