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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Research Project #441209

Research Project: Identifying Landscape Variables and Cropping Patterns Associated with Viral Epidemics in Lettuce

Location: Crop Improvement and Protection Research

Project Number: 2038-22000-020-016-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Nov 1, 2022
End Date: Apr 30, 2025

In recent years, lettuce production in the Salinas Valley was severely impacted by Impatiens necrotic spot virus (INSV). INSV is transmitted by thrips, a tiny insect pest with an extensive host range that includes numerous crops that are part of a diverse agricultural system within the Salinas Valley. While this scenario creates management challenges, there are opportunities to identify landscape variables that influence virus outbreaks. The goals of this proposal are to characterize the migration patterns of thrips between lettuce and non-lettuce crops and identify problematic areas that support populations of thrips vectoring of INSV. Outcomes will result in a greater understanding of cropping and landscape factors that pose the greatest risk for thrips infestations and INSV outbreaks in lettuce crops. The success of this project will be measured by the number of growers and pest control advisors that have gained knowledge and adopted methods to reduce pest and disease risk.

Obj1: Landscape variables influencing thrips migration and INSV infection in lettuce. Lettuce fields within close proximity (100 feet) to other crops or habitats will be selected as treatments. Common crops (e.g., strawberry, broccoli) and habitats (e.g., foothills, riparian), including lettuce and fallow fields will be considered. Insect sticky cards will be placed between lettuce and treatment for a 4-5 week period during the lettuce crop. Data will be gathered on, 1) number of thrips per sticky card between lettuce and treatment, 2) orientation of treatment (N/E/S/W of lettuce), 3) organic or conventional, and 4) INSV incidence in lettuce adjacent to the treatment. 30-50 lettuce fields will be characterized during the 2023 and 2024 seasons. Data will determine relationships between thrips populations and treatments, orientation of treatments, and INSV incidence. Obj2: New technologies to identify thrips populations that are vectoring INSV. Reverse-transcription Recombinase Polymerase Amplification (RT-RPA) technologies will be developed to detect INSV from thrips using primers designed from the NCBI database, and published protocols that describe RT-RPA detection of other RNA viruses. Thrips colonies at the USDA will be used as source material to develop the protocol and set detection limits and thresholds, while standard lab methods (RT-PCR) will be used to validate the technology. Field surveys using RT-RPA assays will be used to screen wild thrips populations for INSV, targeting the same crops and habitats described in Obj1. 100 locations will be surveyed to identify problematic regions that best support thrips populations that are vectoring INSV.