Objective:
Objective 1: Define the distribution patterns of Xylella fastidiosa and Candidatus Liberibacter spp. in planta. Objective 2: Characterize host/pathogen interactions and potential control methods for Candidatus Liberibacter spp. and Citrus.A new sub-objective will be added to the current Objective 2 in ARS Project no. 1275-22000-251-00D: Sub-objective 2A: Improve sensitivity and specificity of Huanglongbing diagnostics utilizing antibody based assays to supplement existing Q-PCR-based assays for use in host plant and insect diagnostic tests. (NP 303; Component 1; Problem Statement 1A). Objective 3: Characterize antagonistic or synergistic interactions between strains of Xylella fastidiosa from sweet orange and grapevine. Objective 4: Establish the etiology of citrus chlorotic dwarf disease. Objective 5: Characterize, using microassay hybridizations and other approaches, host plant gene expression pattern in response to infections by 'Candidatus Liberbacter' spp. (citrus greening pathogens).

Approach:
We will characterize novel or exotic pathogens of citrus that threaten the U.S. citrus industry. This work will include the determination of the etiology of novel diseases, characterization of the diversity present in a pathogenic taxon, the development of diagnostic tests for the pathogen, and the developent of information about disease processes and knowledge that may lead to control of the diseases. This procect will also maintain and develop an extensive collection of exotic pathogens of citrus for use by this project and collaborators from the U.S. and around the world. Detection methods will e generally PCR-based, including real-time quantitative PCR. Antibodies will also be developed. The etiology of novel diseases will be established by plant inocolulations both in the greenhouse in Beltsville and by field experiments in the countries where the disease exists. We will characterize responses of diseased plants to infections by citrus greening pathogens through the use of microarray analyses and other nucleic acid-based approaches and methodologies to identify genes whose expression is altered in infected plants compared to disease-free plants.