Location: Temperate Tree Fruit and Vegetable Research
Project Number: 2092-21220-002-051-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Oct 1, 2019
End Date: Sep 29, 2022
Objective:
Identify non-crop host plants of the beet leafhopper and beet leafhopper transmitted virescence agent (BLTVA) in the Columbia Basin. Define patterns in the movements of beet leafhopper and BLTVA between crop and non-crop hosts, and potato. Improve our understanding of pathogen dynamics in the leafhopper and potato hosts, and develop new tools for detecting BLTVA in the potato host. Disseminate information on plant identification and monitoring, and forecast models to growers and stakeholders.
Approach:
ARS examine the landscape ecology of beet leafhopper by gathering seed from plants from which beet leafhoppers are collected and growing these plants in the greenhouse. Ten plants per species will be used to confirm egg to adult development using standard laboratory approaches. Plants will also be challenged with colony-reared beet leafhoppers infected with BLTVA to confirm the plants’ susceptibility to the pathogen. Additionally, (deoxyribonucleic acid) DNA will be extracted from collected leafhoppers and foliage of potential hosts and will be screened for the presence of BLTVA using diagnostic polymerase chain reaction (PCR).
ARS will examine the landscape-level movements of beet leafhoppers using molecular gut content analysis that identifies plants that the insect previously fed upon by sequencing plant barcoding genes in the gut of the insect. The DNA signal persists in these insects for several weeks, providing a nearly complete history of plants that dispersing insects visited before moving into potato. PCR with universal primers for the chloroplast gene, trnL, and the ribosomal gene, ITS, will be used to amplify plant DNA from the guts of psyllids. Barcoded sequences unique to each sample will be attached to PCR primers so that sequences can be paired with samples after sequencing. PCR products from each sample will be pooled into a single sample to be processed and direct-sequenced using a PacBio platform. Plant sequences will be trimmed and organized into samples based upon the sequences of the barcoded primers. Basic Local Alignment Search Tool (BLAST) search function of the National Central for Biotechnology Information (NCBI) website will be used to identify plant sequences based on similarity to archived sequences. Each leafhopper will also be tested for BLTVA to correlate phytoplasma infection with presence of specific plant DNA in the leafhopper. These data will identify which plant species are reservoirs for beet leafhoppers and BLTVA, and therefore which plant species in the landscape are potential sources of BLTVA-infected leafhoppers entering potato.
Beet leafhopper appears to readily vector BLTVA to potato (and other non-host species) as they move through the landscape in search of reproductive hosts. ARS will examine pathogen dynamics in potato to improve our understanding of BLTVA movement from vector to potato. ARS will determine how rapidly uninfected leafhoppers acquire the pathogen after colonizing infected potato and how rapidly infected leafhoppers transmit the pathogen to potato once they have landed on uninfected potato plants by allowing infected or uninfected beet leafhoppers to feed for specific durations on uninfected or infected potato.
Detecting BLTVA in tissues from known infected plants is notoriously inconsistent. To observe pathogen movement in the potato plant, distribution of BLTVA will be determined in plants originating from infected tubers. Plant tissue will be tested in segments for the presence of the pathogen at different times post-emergence to quantify patterns in localization or movement of BLTVA in tissues.
