|Rotenberg, D - KANSAS STATE UNIV|
|Krishna Kumar, N - INDIAN INST HORT RES|
|Ullman, D - UC DAVIS|
|Montero-Astua, M - KANSAS STATE UNIV|
|German, T - UW MADISON|
|Whitfield, A - KANSAS STATE UNIV|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 20, 2008
Publication Date: April 1, 2009
Citation: Rotenberg, D., Krishna Kumar, N.K., Ullman, D.E., Montero-Astua, M., Willis, D.K., German, T.L., Whitfield, A.E. 2009. Variation in Tomato Spotted Wilt Virus Titer in Frankliniella Occidentalis and Its Association with Frequency of Transmission. Phytopathology. 99(4):404-410. Interpretive Summary: Plant diseases caused by viruses cause billions of dollars of damage to agronomically important crops each year. The problem is compounded by the lack of effective control of viral disease in plants by chemical means or breeding for resistance. Arthropod vectors play an essential role in dissemination of viruses that cause important diseases in humans, animals, and plants. Developing a better understanding of insect–virus interactions leading to successful transmission is vital to developing effective control strategies. Tomato spotted wilt virus (TSWV) is an important pathogen of many crops including tomato, lettuce, and pineapple and is transmitted by thrips insect vectors. In this paper, we show that an infected thrips is more likely to transmit multiple times if it harbors a high titer of virus and that male thrips transmit are more efficient in transmitting virus even though female thrips contain more virus. This work identifies novel biology in virus transmission that will impact the control of virus diseases of important agricultural crops.
Technical Abstract: Tomato spotted wilt virus (TSWV) is transmitted in a persistent propagative manner by Frankliniella occidentalis, the Western flower thrips. While it is well established that vector competence depends on TSWV acquisition by young larvae and virus replication within the insect, the biological factors associated with frequency of transmission have not been well characterized. We hypothesized that the number of transmission events by a single adult thrips is determined, in part, by the amount of virus harbored (titer) by the insect. Transmission time-course experiments were conducted using a leaf disk assay to determine the efficiency and frequency of TSWV transmission following 2-day inoculation access periods (IAPs). Virus titer in individual adult thrips was determined by real-time reverse transcriptase (RT) – PCR at the end of the experiments. On average, 59% of adults transmitted the virus during the first IAP (2-3 days post adult-eclosion). Male thrips were more efficient at transmitting TSWV multiple times compared to female thrips of the same cohort. However, females harbored 2 – 3 times more copies of TSWV- N RNA per insect, indicating that factors other than absolute virus titer in the insect contribute to a successful transmission event. Examination of virus titer in individual insects at the end of the third IAP (7 days post adult-eclosion) revealed significant and consistent positive associations between frequency of transmission and virus titer. Our data support the hypothesis that a viruliferous thrips is more likely to transmit multiple times if it harbors a high titer of virus. This quantitative relationship provides new insights into the biological parameters that may influence the spread of TSWV by thrips.