Research Project: Epidemiology, Vector-Host Plant Interactions, and Biology of Vegetable and Cucurbit Viruses

Location: Crop Improvement and Protection Research

Project Number: 2038-22000-018-000-D
Project Type: In-House Appropriated

Start Date: Aug 13, 2018
End Date: Sep 7, 2022

Objective:
Plant viruses and their vectors cause millions of dollars in losses to vegetable and cucurbit production each year. Molecular characterization of viruses affecting these crops, as well as how they interact with insect vectors, is critical in order to gain an understanding of factors contributing to transmission, disease development, and for the development of accurate and specific diagnostic tools for pathogen identification in crop plants, as well as for development of novel means of virus and vector control. This research will lead to new approaches to reduce vector populations and the ability of vectors to transmit viruses to crop plants, benefitting U.S. industry, growers, and improving food quality for consumers. Objective 1: Identify and compare gene expression changes in insect vectors of plant viruses, such as whiteflies and leafhoppers, and use the information to develop new strategies, such as RNAi, to reduce vector populations and interfere with virus transmission in vegetable and cucurbit crops. • Subobjective 1A: Compare the effect of virus infection of a host plant on feeding behavior and gene expression in whitefly. • Subobjective 1B: Develop strategies for RNAi based control of whitefly in melon and tomato. • Subobjective 1C: Compare the effect of Beet curly top virus (BCTV) infection of a tomato host plant on gene expression in the beet leafhopper (Circulifer tenellus). • Subobjective 1D: Develop strategies for RNAi based control of the beet leafhopper. • Subobjective 1E: Develop strategies to characterize emerging insect pests and viruses in vegetable crops. Objective 2: Identify environmental, physiological, and biological influences leading to development of tombusvirus-induced disease symptoms in lettuce, and use this information to develop crop management recommendations, such as soil fertility regimes, to reduce frequency of disease development. • Subobjective 2A: Conduct RNA sequencing (RNA-seq) of lettuce plants with dieback disease symptoms to determine the presence of additional biotic agents potentially contributing to disease development. • Subobjective 2B: Compare soil treatments to induce lettuce dieback symptoms under controlled conditions, and to understand abiotic factors contributing to disease development in the field. Objective 3: Biologically and molecularly characterize a new torradovirus from California and determine its relationship to other tomato-infecting torradoviruses. • Subobjective 3A: Develop an infectious clone of Tomato necrotic dwarf virus (ToNDV) for use in host range evaluation and further virus characterization. • Subobjective 3B: Evaluate the host range of Tomato necrotic dwarf virus (ToNDV) and differences in vector transmissibility among isolates from tomato and weed hosts. Objective 4. Identify whitefly proteins that interact with virus proteins during transmission of a semipersistently transmitted virus using virus overlay assays and co-precipitation of proteins.

Approach:
1A: Electrical penetration graphing (EPG) will be used to determine whitefly vector feeding patterns in healthy and virus-infected host plants, followed by RNA-sequencing to determine gene expression differences associated with feeding behavior differences between virus-infected and healthy host plants. 1B: Develop strategies for control of whitefly in melon and tomato using RNA interference. Transgenic plants will be developed expressing selected constructs shown to induce RNA interference in preliminary studies, accompanied by development of methods for inducing resistance in non-transformed plants. This should reduce whitefly feeding damage and whitefly-transmitted viruses impact agriculture both in the U.S. and in the developing world. 1C: Comparative gene expression (RNA sequencing) analysis will be used to determine differences in gene expression associated with feeding on either healthy host plants or those infected with the persistent circulative beet curly top virus (BCTV). Results will be compared with previous studies to determine common gene expression changes associated with virus transmission. 1D: Develop strategies for control of leafhopper in tomato using RNA interference and related methods. Transgenic plants will be developed expressing selected constructs shown to induce RNA interference in preliminary studies, accompanied by development of methods for inducing resistance in non-transformed plants. This should reduce transmission of BCTV in tomato and can be applied to several other at-risk hosts. 1E: Develop protocols for studying emerging insect pests and pathogens, insect performance and pathogen transmission in vegetable crops using in-field and laboratory based strategies. Molecular and genetic-based detection tools including, qPCR and ELISA will also be developed to monitor emerging insect pests and pathogens. 2A. Conduct RNA sequencing (RNA-seq) of lettuce plants with dieback disease symptoms to determine the presence of additional biotic agents potentially contributing to disease development. 2B. Compare soil treatments under controlled conditions to identify environmental influences on development of lettuce dieback disease symptoms, and to understand abiotic factors contributing to disease development in the field. Results will improve management recommendations to reduce losses in lettuce. 3A. Develop an infectious clone of the Tomato necrotic dwarf virus (ToNDV) for use in host range evaluations and further characterization of ToNDV, its interactions with host plants and vectors, as well as with other members of the genus, Torradovirus. 3B. Evaluate the host range of Tomato necrotic dwarf virus (ToNDV) and compare differences in vector transmissibility among isolates from tomato and weed hosts, as this will provide important information on virus epidemiology and risk to tomato and other crop hosts in California and the West. 4. Identify whitefly proteins that interact with proteins associated with virus particles during transmission of a semipersistently transmitted virus. Dual binding methods will be used including, but not limited to virus overlay assays and co-immunoprecipitation of proteins.