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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)
2007 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.


4.Accomplishments
Watermelon vine decline has been causing serious economic losses in Florida for the past six growing seasons. Squash vein yellowing virus (SqVYV), a novel pathogen was shown to be the cause of this disease during the previous year’s work. Improved diagnostics for detection of SqVYV were developed during the current year’s research. This technology has been transferred to state regulatory and university diagnostic laboratories to facilitate SqVYV detection, and was used by us in the first report of SqVYV outside of Florida (in Indiana). Addresses National Program Component 1 (Disease diagnosis: Detection, identification and characterization of plant pathogens). Problem Statement 1B: Detection, Identification, Characterization, and Classification of Pathogens

Citrus tatter leaf virus (CTLV) is a quarantine pathogen in regional and national citrus budwood propagation programs and its detection is based on months-long assays for symptom development on citrus assay plants. CTLV causes a rootstock incompatibility on trifoliate orange and trifoliate orange hybrid rootstocks, which are currently used in >50% of the US citrus acreage. A sensitive detection protocol using an immunocapture-reverse transcription-polymerase chain reaction technique was developed to augment or supplant the less sensitive and more time-consuming live plant assays. Application of this technology by regulatory authorities will provide an accurate, rapid and necessary safeguard of citrus germplasm resources. Addresses National Program Component 1 (Disease diagnosis: Detection, identification and characterization of plant pathogens.) Problem Statement 1B: Detection, Identification, Characterization, and Classification of Pathogens

Various viruses were identified in weeds, ornamentals and vegetables during the 2006-2007 growing season in Florida and beyond. This included the several new host/location reports for known viruses, and also reports of several previously undescribed viruses. Alerted to the presence of these vegetable and ornamental pathogens, growers can make appropriate management decisions. Addresses National Program Component 2 (Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors). Problem Statement 1B: Detection, Identification, Characterization, and Classification of Pathogens

Multi-pest, statewide, citrus exotic pest sampling method; A method was needed by state and federal regulatory agencies to quickly survey the entire state of Florida for newly introduced exotic pathogens. We expanded a previous stochastic statewide stratified sampling/survey program for huanglongbing (HLB)/canker to include citrus variegated chlorosis (CVC) and be adaptable for the addition of future pest and pathogens. The new MPS multi-pest sampling/survey program was immediately adopted and is being utilized to determine the distribution of HLB, canker, and CVC in commercial citrus throughout Florida. In the future the MPS will be adaptable to California and Texas statewide citrus industries as well. Addresses National Program Component 2 (Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors). Problem Statement 1B: Detection, Identification, Characterization, and Classification of Pathogens and Problem Statement 2C: Population Dynamics, Spread, and Epidemiology of Pathogens

Characteristics of citrus canker symptom assessment; Citrus canker (Xanthomonas axonopodis pv citri) causes major epidemics in commercially important citrus species and cultivars and monitoring the disease, study epidemics and assess breeding material disease assessment needs to be accurate, precise and repeatable but can be problematic. Visual assessment was compared to the ‘actual’ values measured by image analysis and assumed to be the more precise and accurate when comparing lesion counts and total % area showing symptoms of necrosis+chlorosis and % area with necrosis estimated. It was found that there was a general tendency to overestimate that was inversely proportional to the log area, and sensitive to lesion number; consequently variance of the estimate was found to increase up to at least 25% area infected. Training in assessment will doubtless improve the repeatability and reproducibility of assessment. Addresses National Program Component 2 (Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors). Problem Statement 2C: Population Dynamics, Spread, and Epidemiology of Pathogens. Problem Statement 4A: Biological and Cultural Control Technologies

Citrus canker survival through packinghouse decontamination treatments; USDA/APHIS and regulatory agencies in Californai and Texas are concerned about canker-infected fruit as a pathway for canker infection to citrus production areas new areas. Survival studies with canker-infected and noninfected fruit combinations were conducted in Florida, Argentina, and Brazil to examine survival characteristics. In all three locations, a few bacteria were recoverable after packinghouse processing and decontamination treatment and post-processed fruit in discarded cull piles did not function as a source of infection for susceptible young grapefruit trees located 1, 5 and 10 meters from the piles. These finding are in concurrence with the USDA, APHIS Pest Risk Assessment and Risk Management Analysis on ‘Movement of Commercially Packed Citrus Fruit form Citrus Canker Disease Quarantine Areas’, and thus may have impact on interstate and international shipment of citrus fruit. Addresses National Program Component 2 (Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors). Problem Statement 2B: Plant-Microbe-Vector Interactions. Problem Statement 2C: Population Dynamics, Spread, and Epidemiology of Pathogens

Rapid identification and differentiation of citrus bacterial diseases (canker and Burkholderia brown leaf spot). Citrus canker is one of the most important citrus diseases in Florida, and is imposing immediate threat on the citrus industry in California and Texas. Elucidates the variation of citrus canker strains are critical important for quarantine and disease managements. A novel primer, along with PCR protocol was developed to identify and differentiate strains of citrus canker bacteria (X. citri axonopodis pv. citri), and Burkholderia brown leaf spot (a new bacterial disease of citrus, Burkholderia andropogonis). Molecular characterization of the newly identified citrus canker strain from Florida revealed unique molecular characteristics in this slow-inducing canker strain. The identification of this strain implicated the potential importance of its role in citrus canker epidemiology and survival through post-harvest. This technology has been transferred to state regulatory and university research laboratories to facilitate citrus canker strain identification and differentiation. Addresses National Program Component 1 (Disease diagnosis: Detection, identification and characterization of plant pathogens). Problem Statement 1B: Detection, Identification, Characterization, and Classification of Pathogens. Problem Statement 2A: Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen

Development of high throughput detection technology for citrus huanglongbing (HLB). Citrus huanglongbing, the most devastating citrus disease, is now wide-spread in Florida, and is imposing immediate threat to the citrus industry in California and Texas. Because of the fastidious nature of HLB bacteria (Candidatus Liberibacter asiaticus), a high throughput detection technology for HLB is critical important for HLB research and disease management. Polyclonal antibodies against HLB pathogen have been developed, and a series of primers and probes were also developed for better detection of HLB using PCR or in situ hybridization. These technologies have been transferred to university and state regulatory research laboratories for HLB detection and other research purposes. Addresses National Program Component 1 (Disease diagnosis: Detection, identification and characterization of plant pathogens). Problem Statement 1B: Detection, Identification, Characterization, and Classification of Pathogens.

Epidemiological studies of watermelon vine decline, caused by Squash vein yellowing virus, are hampered by our inability to adequately quantify the virus in production fields. A survey was conducted to determine the within-plant distribution of the virus over the course of the epidemic. Results indicated that the virus could be detected in nearly all vines of infected plant, but the probability of detection was greatest towards the basal portion of the vine. Moreover, it appears that the ability to detect the virus was greatest in the early stages of infection. Knowledge of the distribution will permit more efficient large scale sampling of fields and eliminates the need for full-plant destruction in these types of surveys. Addresses National Program Component 2 (Biology, ecology, epidemiology, and spread of plant pathogens and their relationships with hosts and vectors). Problem Statement 1B: Detection, Identification, Characterization, and Classification of Pathogens and Problem Statement 2C: Population Dynamics, Spread, and Epidemiology of Pathogens.


5.Significant Activities that Support Special Target Populations
None.


6.Technology Transfer

Number of non-peer reviewed presentations and proceedings37
Number of newspaper articles and other presentations for non-science audiences5

Review Publications
Adkins, S.T., Mcavoy, G., Rosskopf, E.N. 2007. Tropical soda apple mosaic virus Identified in Solanum capsicoides in Florida. Plant Disease. 91:1204

Egel, D., Adkins, S.T. 2007. Squash vein yellowing virus identified in watermelon in Indiana. Plant Disease. 91:1056.

Baker, C.A., Kamenova, I., Adkins, S.T. 2007. Bidens mottle virus identified in tropical soda apple in florida. Plant Disease. 91:905.

Baker, C.A., Adkins, S.T. 2007. Tobacco ringspot virus found in the Cardboard Cycad, Zamia furfuracea, in Florida. Plant Disease. 91:112.

Adkins, S.T., Webb, S., Achor, D., Roberts, P., Baker, C. 2007. Identification and characterization of a novel whitefly-transmitted member of the family potyviridae isolated from cucurbits in florida. Phytopathology. 97:No. 2, 145-154.

Irey, M.S., Gottwald, T.R., Graham, J., Riley, T., Carlton, G. 2006. Post-hurricane analysis of citrus canker spread and progress towards the development of a predictive model for future weather related spread. Plant Health Progress.

Gent, D.H., Mahaffee, W.F., Turechek, W. 2006. Spatial Heterogeneity of the Incidence of Powdery Mildew on Hop Cones. Plant Disease.

Benson, D., Grand, L., Vernia, C., Gottwald, T.R. 2006. Temporal and spatial epidemiology of phytophthora root rot in fraser fir plantations. Plant Disease. 90:1171-1180.

Gottwald, T.R., Bassanezi, R., Amorim, L., Bergamin-Filho, A. 2007. Spatial pattern analysis of citrus canker infected plantings in São Paulo, Brazil and implication of the asian leafminer on the potential dispersal processes. Phytopathology. 97:674-683.

Irey, M.S., Gast, T., Gottwald, T.R. 2006. Comparison of visual assessment to polymerase chain reaction assay testing to estimate the incidence of the huanglongbing pathogen in commercial plantings in florida. Proceedings of Florida State Horticultural Society. 42:17-21.

Novelli, V., Freitas-Astua, J., Arrivabem, F., Locali, E., Hilf, M.E., Gottwald, T.R., Machado, M. 2007. Influence of the storage period and number of individuals on the detection of false spider mite endosymbionts. Experimental and Applied Acarology. 42:17-21.

Gottwald, T.R. 2006. Plum pox - review of PPV epidemiology in North America. European and Mediterranean Plant Protection Organization Bulletin. 36:269-286.

Gottwald, T.R., Irey, M.S. 2007. Post-hurricane analysis of citrus canker ii: predictive model estimation of disease spread and area potentially impacted by various eradication protocols following catastrophic weather events. Plant Health Progress. doi:10.1094/PHP-2007-0405-01-RS.

Adkins, S.T., Kamenova, I., Rosskopf, E.N., Lewandowski, D. 2007. Identification and characterization of a novel tobamovirus from tropical soda apple in Florida. Plant Disease. 91:287-293.

Dewdney, M., Biggs, A., Turechek, W. 2007. A statistical comparison of the blossom blight forecasts of maryblyt and cougarblight with receiver operating characteristic curve analysis. Phytopathology. 97:1164-1176.

Zhou, L., Gabriel, D., Duan, Y., Halbert, S., Dixon, W. 2007. First Report of Dodder Transmission of Huanglongbing from Naturally Infected Murraya paniculata to Citrus. Plant Disease. 91:22.

Al-Saadi, A., Reddy, J., Duan, Y., Brunings, A.M., Gabriel, D.W. 2007. All Five Host-Range Variants of Xanthomonas citri Carry One pthA Homolog With 17.5 Repeats That Determines Pathogenicity on Citrus, but None Determine Host-Range Variation. Molecular Plant-Microbe Interactions. 20:934-943

Gent, D.H., Turechek, W., Mahaffee, W.F. 2007. Sequential sampling for estimation and classification of the incidence of hop powdery mildew I: Leaf sampling. Plant Disease. 91:1002-1012.

Gent, D.H., Turechek, W., Mahaffee, W.F. 2007. Sequential sampling for estimation and classification of the incidence of hop powdery mildew II: Cone sampling. Plant Disease. 91:1013-1020.

Last Modified: 11/26/2014
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