1a.Objectives (from AD-416):
The project addresses the dynamics of annual virus infections of tomato by identifying and differentiating important reservoir hosts of tomato viruses that facilitate transmission to the crop from those that are poor sources for transmission, identifying key viruses in new areas of processing tomato production, and monitoring vector incidence (sticky cards) in correlation with virus incidence. The overall goal is to develop targeted IPM strategies to minimize impact of viruses on tomato production based on knowledge of epidemiology including important reservoir hosts and vectors by region.
1b.Approach (from AD-416):
Monitor transmission of Beet mild curly top virus and Beet severec curly top virus from tomato and alternate crop and weed hosts in relation to virus concentration in the host plant. Determine population dynamics of vectors using standard methodologies. These laboratory/greenhouse level studies will determine the significance of crop and weed hosts long thought to be reservoirs, and determine their importance or lack of importance epidemiologically using modern technology.
This project relates to Subobjective 2C, Identification of factors influencing emergence and dominance of curtoviruses in North America. Methods have been developed for routine detection of the three primary curtoviruses affecting tomato, Beet severe curly top virus (BSCTV), Beet mild curly top virus (BMCTV), and the older, less common Beet curly top virus (BCTV) using a single reaction multiplex PCR system that rapidly identifies the infecting virus. A second system of quantitative (real-time) PCR (qPCR) has also been developed to determine concentration of each curtovirus in tomato and other host plants. We recently developed and are testing a new multiplex RT-PCR detection system for additional tomato infecting viruses frequently found infecting California tomatoes. Studies are examining differences in concentration of curtovirus species from single and mixed infections in wild and cultivated hosts using the qPCR methods described above, and are examining how source concentration relates to transmission. Field components involved monitoring movement of beet leafhopper and incidence of each virus among several locations along the western foothills of the San Joaquin Valley. Leafhopper populations peaked significantly at different times in each of three areas in June, with only low numbers in the other locations. Leafhopper populations overall were exceptionally low, and were consistent with results obtained by the CDFA curly top control board. Virus incidence in tomato fields and among weed and crop hosts has also been low for the past two years making population studies challenging, however, numerous samples from several host plants have now been characterized.