Location: Crop Improvement and Protection Research
Project Number: 2038-22000-020-000-D
Project Type: In-House Appropriated
Start Date: Sep 8, 2022
End Date: Sep 7, 2027
Plant viruses and their vectors cause millions of dollars in losses to vegetable production each year through decreased yield, quality, and plant longevity, as well as the need for regular pesticide application. Research is necessary to understand factors driving the emergence of and changes in the prevalence of new viruses, as well as to develop more environmentally friendly control methods. This research will lead to safer and more sustainable practices for management of vector populations, reduce transmission of viruses to crop plants, benefit the U.S. vegetable industry and growers, and improve food quality for consumers. Objective 1: Characterize the epidemiology of and interactions between insects and insect-transmitted viruses to understand their distribution and threat to vegetable crop production. Sub-objective 1.A: Conduct field surveys to identify the host range for thrips-transmitted tospoviruses affecting lettuce production in California and Arizona. Sub-objective 1.B: Characterize the genetic variation of Impatiens necrotic spot virus (INSV) isolates using RNA sequencing. Sub-objective 1.C: Evaluate soil-borne organisms as potential vectors of lettuce dieback associated virus (LDaV). Sub-objective 1.D: Compare competitive binding of cucurbit chlorotic yellows virus (CCYV) and cucurbit yellow stunting disorder virus (CYSDV) (both genus Crinivirus, Closteroviridae) in whitefly vectors and how this relates to preferential transmission of one virus over the other. Objective 2: Develop resources to identify and monitor vegetable crops for introduction or emergence of novel viruses and vectors. Sub-objective 2.A: Develop monitoring strategies for identifying thrips vector species and thrips-transmitted viruses using genetic markers. Sub-objective 2.B: Develop and validate molecular methods for detection of torradoviruses that infect vegetable crops. Objective 3: Develop biotechnology tools, such as RNA interference to create new tools for managing insects and insect-transmitted viruses affecting vegetables. Sub-objective 3.A: Develop RNA interference (RNAi) technologies for managing insects and insect-transmitted viruses, including thrips, whiteflies, and leafhoppers. Sub-objective 3.B: Evaluate precision-spray technologies for managing insects and insect-transmitted viruses. Sub-objective 3.C: Evaluate plant immune priming agents for managing insect-transmitted viruses.
1A. Field surveys will be conducted to determine the presence of impatiens necrotic spot virus (INSV) in symptomatic and asymptomatic plant species that are common in lettuce production areas. Symptomatic and asymptomatic plants will be sampled across four locations including different habitats and tested for presence of INSV to identify alternate hosts. 1B. Full genomes of current and archived isolates of INSV samples from lettuce will be determined using Oxford Nanopore or Illumina sequencing methods. Based on the outcomes of these studies, genetic markers will be identified for any unique INSV isolates and PCR primers will be developed to amplify the genetic region. This will allow more rapid determination of the prevalence of different virus variants. 1C. Soil-borne root-associated organisms will be isolated from soil and virus-free isolates characterized and propagated. This virus-free culture will be exposed to virus infected lettuce and other host plants in an attempt to determine if the soil-borne organisms can acquire the virus. Lettuce will be grown in these soils and tested for virus incidence to determine if the soil-borne organism can transmit the virus to lettuce. 1D. Confocal microscopy and fluorescent in situ hybridization will be used to compare competitive differential binding of two closely related whitefly-transmitted viruses. This will contribute to determining what influences differential transmission and virus species dominance in agricultural ecosystems. 2A. Available genetic information will be used to design primers to differentiate thrips species common in the Salinas Valley from one another, and these will be used to identify thrips species and their host range among regional plants. 2B. Multiplex (multiple primers in a single reaction) and virus-specific primers will be designed against known torradovirus sequences and specificity confirmed against target and non-target virus isolates. Methods will aid in identification of torradoviruses in imported plant material. 3A. Genetic targets to western flower thrips (Frankliniella occidentalis), and beet leafhopper (Circulifer tenellus) will be identified for suppression using RNAi strategies. In vitro testing will be used to evaluate effectiveness of RNAi against insect pest targets and against non-target insects. Methods will lead to novel methods to suppress populations of these important virus vectors. 3B. Field trials will be conducted to evaluate precision spray technologies to optimize performance of reduced pesticide application methods for control of thrips on commercial lettuce. Results will be compared directly with conventional approaches. 3C. Commercially available agents that activate plant defenses against pathogens will be evaluated to determine their efficacy in protecting lettuce from impatiens necrotic spot virus (INSV), an important thrips-transmitted virus threatening lettuce production. Agents with high level performance will be combined with reduced pesticide application programs to enhance control of INSV in lettuce.