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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Crop Diseases, Pests and Genetics Research » Research » Research Project #436008

Research Project: Geographic Distribution of Isolate Virulence in Xylella Fastidiosa Collected From Grape in California and its Effect on Host Resistance

Location: Crop Diseases, Pests and Genetics Research

Project Number: 2034-21220-007-19-A
Project Type: Cooperative Agreement

Start Date: Dec 1, 2018
End Date: Jun 30, 2021

This proposal seeks to determine virulence (level of disease caused by a given individual isolate) diversity of Xylella fastidiosa (Xf) subsp. fastidiosa in California (CA) to enhance host resistance to Pierce’s Disease (PD). The specific objectives of the proposal are to 1) Evaluate virulence diversity of Xf strains from California and 2) Evaluate known sources of PD resistance against diverse strains of Xf.

Virulence assessments in tobacco will be conducted in the greenhouse facilities at Auburn University. Plants will be grown in the greenhouse and fertilized monthly. In addition to the California strains, ~10 strains isolated from grapes in Georgia and Florida will be used for comparison. For inoculation, strains will be resuspended in succinate buffer and pin-prick inoculated. Control plants will be inoculated with buffer only. Symptom development will be assessed weekly for approximately 2-3 months. Parameters to be considered will be timing and severity of symptoms and bacterial proliferation and movement. During two time-points (at the beginning and full onset of leaf scorch symptoms) petiole samples will be collected at different positions in plants and Xylella fastidiosa (Xf) populations will be quantified by quantitative polymerase chain reaction (qPCR) to assess movement inside the xylem. The experiments will be organized as a complete randomized block. Each treatment will consist of ten plants, and the experiments will be independently replicated three times. Assessment of disease incidence and severity over time will be used to calculate area under the disease progress curve (AUDPC) for each strain. Data of all experiments will be tested by statistical analysis.