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United States Department of Agriculture

Agricultural Research Service

Research Project: DOMESTIC, EXOTIC, AND EMERGING DISEASES OF CITRUS, VEGETABLES, AND ORNAMENTALS (DEED)
2008 Annual Report


1a.Objectives (from AD-416)
Three broad objectives guide this project: Objective 1: Characterize ecology, biology, epidemiology, genetics and host interactions of domestic, exotic, newly emergent and re-emerging pathogens. Objective 2: Develop/refine rapid, sensitive reliable detection/sampling methods for pathogens. Objective 3: Develop or improve comprehensive integrated disease management strategies.


1b.Approach (from AD-416)
The overall approach is to thoroughly characterize new exotic and emerging plant pathogens at multiple levels: epidemiologically epidemics will be followed and modeled by traditional and newer stochastic methods at the regional, and plantation levels, biologically the pathosystems will be characterized at the level of host-pathogen-vector interaction, as well as at the cellular, molecular and/or biochemical levels. New pathogens will be identified and characterized by molecular biological and traditional cultural methods. Recombinant DNA and genomics technologies will be applied to study host/pathogen interactions and to investigate virulence differences between strains of a pathogen. New CTV genotypes will be identified by cloning products obtained by PCR and degenerate primers and also by hybridization to a sequencing microarray. Primers for PCR diagnostics will be devised from novel CTV genotypes. An immunocapture-based PCR protocol will be developed for CTLV for assessment of genetic variability of CTLV populations from the US and from international locations.


3.Progress Report
Cloning and sequencing of various pathogens including Candidatus Liberibacter asiaticus, tomato spotted wilt virus (TSWV), squash vein yellowing virus (SqVYV), Xanthomonus axonopodis pv. citri (Xac) was continued and/or completed in the current reporting period. Pathogen-insect and pathogen-host interaction/transmission studies were also continued or completed. Wind tunnel and fan experiments to simulate spread of canker and huanglongbing (HLB) were designed and initiated, and data from these experiments were used to initiate design of epidemic simulation software. Sequences of citrus tristeza virus (CTV) and citrus tattered leaf virus (CTLV) were obtained and weed hosts for citrus leprosis virus (CiLV) and SqVYV were identified as potential pathogen reservoirs. Various diagnostic tools and reagents were developed for a wide spectrum of pathogens within the project; validation was initiated. Hyperspectral (HS) data was collected from Xac-infected plants and volatiles were collected and evaluated from HLB infected plants. Data collection was completed for HS sampling method for HLB and a corrected HS sampling protocol for HLB was developed. Preliminary stochastic and meso-scale weather models for epidemics were developed. Screening of watermelon germplasm for resistance to SqVYV, whitefly transmission of SqVYV and epidemiology of SqVYV and other cucurbit-infecting viruses were continued or initiated. Tobamovirus sanitation trials were initiated in vegetatively propagated ornamentals. Various viruses were identified in weeds, ornamentals and vegetables during the 2007-2008 growing seasons. This included several new host/location reports, and also reports of two additional whitefly-transmitted cucurbit viruses, Cucurbit leaf crumple virus (CuLCrV) and Cucurbit yellow stunting disorder virus (CYSDV) in Florida cucurbit crops. CuLCrV is now established in the state and, like SqVYV, found in common cucurbit weeds. CuLCrV has also been identified in green beens. Alerted to the presence of these pathogens, growers can make appropriate management decisions.

Addresses National Program 303 Plant Diseases, Component 1 Disease diagnosis: Detection, identification and characterization of plant pathogens and Component 2 Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors.


4.Accomplishments
1. Watermelon vine decline caused by Squash vein yellowing virus (SqVYV) has been responsible for losses in Florida over the past six growing seasons. The SqVYV genome was sequenced/analyzed and several common cucurbit weeds that can serve as SqVYV reservoirs were identified.

Addresses National Program 303 Plant Diseases Component 1 Disease diagnosis: Detection, identification and characterization of plant pathogens, Problem Statement 1B Detection, Identification, Characterization, and Classification of Pathogens and Component 2 Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors, Problem Statement 2A Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen.

2. Complementary deoxyribonucleic acid (cDNA) libraries were created to screen for molecular sequences of the uncharacterized virus-like pathogen causing the citrus disease citrus concave gum. Sequences are being screened for molecular signatures indicative of pathogens.

Addresses National Program 303 Plant Diseases Component 1 Disease diagnosis: Detection, identification and characterization of plant pathogens, Problem Statement 1B Detection, Identification, Characterization, and Classification of Pathogens and Component 2 Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors, Problem Statement 2A Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen.

3. Developing high throughput detection technology for citrus huanglongbing (HLB). HLB, the most devastating citrus disease, is now widespread in Florida, and is an impending threat to the citrus industries in California and Texas. The HLB bacterium (Candidatus Liberibacter asiaticus) is not culturable so a high throughput detection technology is critically important for HLB research and disease management. Polyclonal antibodies against HLB pathogen and a series of nested polymerase chain reaction (PCR) primers and probes were developed and evaluated for better detection of HLB. These technologies have been transferred to university and state regulatory laboratories for diagnostic and basic research purposes.

Addresses National Program 303 Plant Diseases Component 1 Disease diagnosis: Detection, identification and characterization of plant pathogens, Problem Statement 1B Detection, Identification, Characterization, and Classification of Pathogens and Component 2 Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors, Problem Statement 2A Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen.

4. Only limited Candidatus Liberacter (Ca. L.) asiaticus sequences (less than 50 kb) of three genetic loci available in Genebank. A draft genome sequence of Ca. L. asiaticus has been completed with 1,216,073 bp in 38 large contigs. Annotation of the draft genome revealed 1161 open reading frames, of which 81.0% had functional assignment. We estimate that over 95% of the genome sequence has been obtained. All sequences have been submitted to GenBank and shared with ARS and university researchers to facilitate HLB research.

Addresses National Program 303 Plant Diseases Component 1 Disease diagnosis: Detection, identification and characterization of plant pathogens, Problem Statement 1B Detection, Identification, Characterization, and Classification of Pathogens and Component 2 Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors, Problem Statement 2A Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen.

5. Epidemiological studies of viral watermelon vine decline, caused by squash vein yellowing virus (SqVYV), are hampered by lack of knowledge of how the virus is dispersed in plants in either single or mixed infections with cucurbit leaf crumple virus (CuLCrV) or cucurbit yellow stunting disorder virus (CYSDV) in watermelon. The within-plant distribution of the virus was determined over the course of an epidemic. Results showed that distribution of SqVYV in vine tissue decreased proportionately with distance from the crown. In contrast, CuLCrV was generally evenly distributed throughout the vine, but a slightly higher incidence could be detected at distances farthest from the crown. The results indicate that SqVYV and CuLCrV are somewhat spatially separated in watermelon vines, and this may have an impact on dissemination.

Addresses National Program 303 Plant Diseases, Component 2 Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors, Problem Statement 2B Plant-Microbe-Vector Interactions and Problem Statement 2C Population Dynamics, Spread, and Epidemiology of Pathogens Problem; and Component 4 Biological and Cultural Strategies for Sustainable Disease Management, Problem Statement 4A Biological and Cultural Control Technologies.

6. Multi-pest, statewide, citrus exotic pest sampling method. State and federal regulatory agencies needed methods to quickly survey the entire state of Florida for newly introduced exotic pathogens. In 2008 we expanded a previous stochastic statewide stratified sampling/survey program for HLB/canker/citrus variegated chlorosis (CVC), to include Citrus leprosis virus (CiLV); the survey is further adaptable if needed for future pest and pathogens. The revised multi-pest sampling/survey program was immediately re-adopted and is being utilized to determine the distribution of HLB, canker, CVC, and CiLV in commercial citrus throughout Florida. The MPS will be adaptable to California and Texas statewide citrus industries as soon as data is provided from those states/regulatory agencies. Addresses National Program 303 Plant Diseases, Component 2 Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors, Problem Statement 2B Plant-Microbe-Vector Interactions and Problem Statement 2C Population Dynamics, Spread, and Epidemiology of Pathogens Problem; and Component 4 Biological and Cultural Strategies for Sustainable Disease Management, Problem Statement 4A Biological and Cultural Control Technologies.


5.Significant Activities that Support Special Target Populations
None.


6.Technology Transfer

Number of Non-Peer Reviewed Presentations and Proceedings2
Number of Newspaper Articles and Other Presentations for Non-Science Audiences3
Number of Other Technology Transfer1

Review Publications
Gottwald, T.R., Da Graca, J.V., Bassanezi, R.B. 2007. Citrus Huanglongbing: The Pathogen and Its Impact. Plant Health Progress. Online: doi:10.1094/PHP-2007-0906-01-RV.

Gottwald, T.R. 2007. Citrus Canker and Citrus Huanglongbing, Two Exotic Bacterial Diseases Threatening the Citrus Industries of the Western Hemisphere. Outlooks on Pest Management. 18(6):274-9.

Weng, Z., Barthelson, R., Gowda, S., Hilf, M.E., Dawson, W., Galbraith, D., Xiong, Z. 2007. Persistent infection and promiscuous recombination of multiple genotypes of an RNA virus within a single host generate extensive diversity.. PLoS One. 2(a):e917.doi:10.1371/journal.pone.0000917.

Li, W., Adkins, S.T., Hilf, M.E. 2007. Characterization of complete sequences of RNA 1 and RNA 2 of citrus variegation virus. Archives of Virology. 153:385-388.

Li, W., Hilf, M.E., Webb, S.E., Baker, C.A., Adkins, S.T. 2008. Presence of P1b and absence of HC-Pro in Squash vein yellowing virus suggests a general feature of the genus Ipomovirus in the family Potyviridae. Virus Research. 135:213-219.

Adkins, S.T., Webb, S., Baker, C., Kousik, C.S. 2008. Squash vein yellowing virus detection using nested polymerase chain reaction demonstrates Momordica charantia is a reservoir host. Plant Disease. 92:1119-1123.

Baker, C.A., Rosskopf, E.N., Irey, M.S., Jones, L., Adkins, S.T. 2008. Bidens mottle virus and Apium virus Y identified in Ammi majus in Florida. Plant Disease. 92:6:975.

Turechek, W., Hartung, J.S., Mccallister, J.E. 2008. Development and Optimization of a Real Time Detection Assay for Xanthomonas fragariae in Strawberry Crown Tissue with Receiver Operating Characteristic (ROC) Curve Analysis. Phytopathology. 98(3):359-368.

Biggs, A., Turechek, W., Gottwald, T.R. 2008. Analysis of fire blight shott infection epidemics on apple. Plant Disease. 92:1349-1356.

Behlau, F., Belasque Jr., J., Bergamin-Filho, A., Graham, J., Leite, Jr., R., Gottwald, T.R. 2008. Copper Sprays and Windbreaks for Control of Citrus Canker on Young Orange Trees in Southern Brazil. Crop Protection Journal. 27:807-813.

Duan, Y., Zhou, L., Gottwald, T.R., Gabriel, D. 2008. First Report of Dodder Transmission of Candidatus Liberibacter asiaticus to Tomato (Lycopersicon esculentum). Plant Disease. 92:831.

Hilf, M.E., Garnsey, S., Robertson, C., Gowda, S., Satyanarayana, T., Irey, M., Sieburth, P., Dawson, W. 2007. Characterization of Recently Introduced HLB and CTV Isolates. Proceedings of Florida State Horticultural Society. 120:138-141.

Montero-Astua, M., Vasquez, V., Turechek, W., Merz, U., Rivera, C. 2008. Incidence, distribution and association of Spongospora subterranea and Potato mop-top virus in Costa Rica. Plant Disease. 92:1171-1176.

Loughner, R., Loeb, G., Turechek, W. 2007. Strawberry sap beetle (Coleoptera: Nitidulidae) distribution in New York and differential movement in two types of habitat. Journal of Entomological Science. 42:603-609

Akad, F., Webb, S., Nyoike, T., Liburd, O., Turechek, W., Adkins, S.T., Polston, J. 2008. Detection of Cucurbit leaf crumple virus in Florida cucurbits. Plant Disease. 92:648.

Cook, A., Gibson, G., Gottwald, T.R., Gilligan, C. 2008. Constructing the effect of alternative intervention strategies on historic epidemics. Proceedings of the Royal Society of London B. doi:10.1098/rsif.2008.0030

Bock, C.H., Parker, P., Cook, A., Gottwald, T.R. 2008. Characteristics of the perception of different severity measures of citrus canker and the relations between the various symptom types. Plant Disease. 92:927-939.

Bock, C.H., Parker, P., Cook, A., Gottwald, T.R. 2008. Visual rating and the use of image analysis for assessing different symptoms of citrus canker on grapefruit leaves. Plant Disease. 92:530-541.

Hilf, M.E. 2008. An Immunocapture RT-PCR Procedure Using Apple stem grooving virus Antibodies Facilitates Molecular Genetic Characterization of Citrus tatter leaf virus from the Original Meyer Lemon Host. Plant Disease. 92:746-750.

Last Modified: 10/21/2014
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