ARS: Citrus Greening
Huanglongbing (Citrus Greening): What ARS Is
Doing
Huanglongbing (HLB), also known as Citrus Greening
disease because fruit tends to turn green after ripening, undoubtedly poses the
most serious threat that the Florida citrus industry has ever faced. The
bacteria that cause HLBthree species of Liberibacterprobably
originated in China in the early 1900s. In countries where the disease is
endemic, citrus trees begin to decline within 5 to 8 years after planting and
rarely bear usable fruit.
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First detected in Florida in 2005; by 2008, it had been
identified in most of the citrus growing counties in the state. Despite
everyone's best efforts, HLB now literally threatens the survival of Florida
citrus and is a potential threat to the entire U.S. citrus industry.
ARS scientists are actively engaged in research with
university and industry partners on the critical components of this disease
such as etiology and epidemiology, the insect vector, and the plant host's
response to HLB infection.
In February 2008, members of the citrus industry
requested additional input from ARS scientists, especially from researchers
outside of the citrus field, to draw on the most diverse expertise possible to
elicit new ideas about research needs, gaps, priorities, and
opportunities.
In response, ARS convened a workshop in April 2008 at the
U.S. Horticultural Research Laboratory in Fort Pierce, Florida, especially
inviting ARS scientists who are leaders in their scientific fields but who are
not ordinarily engaged in citrus research. These ARS scientists brought their
collective expertise in animal and plant entomology, animal and plant
pathology, genetics, horticulture, and microbiology to the workshop. The
workshop was coordinated with the National Academy of Sciences (NAS), which had
been asked by the Florida Department of Citrus to develop a Request for
Proposals to manage grant funding for research leading to HLB management.
That meeting was followed in May 2008 by a workshop in
Beltsville, Maryland, of key ARS citrus researchers to discuss potential new
collaborations and research directions to address the needs identified at the
April 2008 workshop.
On September 17-18, 2008, a group of ARS scientists,
industry and university representatives from citrus producing states met with
the federal regulatory agencies USDA-APHIS, FDA, and EPA to prepare for the
advent of transgenic citrus to be used to combat HLB and canker to seek
guidance on bringing these products to market.. This meeting was an excellent
opportunity for each party to learn about what will be needed as progress is
made toward this goal. Other potential new chemicals for insect control and
management of the pathogen in citrus were also discussed. A team of scientists
are preparing documents that summarize published data on citrus biology,
pollination, gene flow and juice composition parameters; information that will
be needed by the regulatory agencies as transgenic citrus products are
developed.
Current ARS Research
ARS has initiated a significant research program, even
before the 2008 workshops.
ARS scientists have established partnerships with
industry and university colleagues, and these collaborations continue to grow
and diversity as new knowledge is developed. The ultimate goal is to
effectively manage major threats to the citrus industry in the U.S., in
particular, citrus greening, or HLB, and canker. A broad approach is being
taken to target the main components of the disease triangle; the host, the
pathogen and associated organisms, and the insect vector. Insect management,
repellants and control are critical to disease control. Manipulating citrus
groves by varying nutrition and high density planting may reduce the impact of
the diseases. As scientists learn more about the bacterium associated with HLB,
methods for directly impacting its growth in the citrus host will be devised.
Conventional breeding and genetically modified citrus varieties are being
explored. All of these components of disease intervention are being
investigated by ARS scientists and colleagues, and will be utilized for to
benefit the national citrus industry.
Accomplishments
Because of the fastidious nature of HLB bacteria
(Candidatus Liberibacter asiaticus), a high-throughput detection technology for
HLB is critical for HLB research and disease management. Polyclonal antibodies
against HLB pathogen have been developed by researchers at Fort Pierce,
Florida, 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.
ARS scientists at Frederick, Maryland, determined the
effect of imidacloprid insecticide on transmission of HLB. Following
incorporation of the insecticide into sweet orange seedlings, infectious
psyllids were aspirated on the seedlings and monitored for survival and disease
transmission. Although most psyllids died within the first 24 hours, strong
symptoms of HLB infection were evident by 8 weeks in most plants, indicating
the insects could transmit the causal HLB bacterium before dying.
ARS scientists at Beltsville, Maryland developed and
validated the first real-time and quantitative PCR assay for the greening
pathogen. This assay was used by the USDA Animal and Plant Health Inspection
Service (APHIS) and the Florida Department of Agriculture to confirm the
presence of HLB in Florida. Producers will benefit from early detection and
genetic improvement for resistance will be accelerated.
ARS scientists at Ft. Pierce and colleagues recently
published the full genomic sequence of HLB bacterium, 'Candidatus
Liberibacter asiaticus'. This is a major scientific advance, and will enable
scientists to identify genes responsible for the disease, enhance capabilities
to culture this organism and determine its true role as the causal agent.
Scientists at Ft. Pierce have evidence that suggests that
guava, interplanted with citrus, prevents the spread of greening. Scientists in
Japan and Viet Nam discovered that HLB did not occur in citrus groves when
intercropped with guava, while control plots had over 30 percent infection. The
mechanism may be volatile compounds produced by guava which disrupt the ability
of the psyllid vector of HLB to locate its citrus host. Studies are underway in
field plots to validate these preliminary findings and to identify the
potential volatiles.
ARS Research Projects on Huanglongbing
(Citrus Greening)
Exotic
Pathogens of Citrus
LEAD SCIENTIST: John S. Hartung, Beltsville, Maryland
IPM
Technologies for Subtropical Insect Pests
LEAD SCIENTIST: David Hall, Fort Pierce, Florida
Identification,
Characterization, and Biology of Foreign and Emerging Insect-Transmitted Plant
Pathogens
LEAD SCIENTIST: Vernon D. Damsteegt, Ft. Detrick, Maryland
Identification,
Characterization, and Detection of Foreign and Newly Emerging Domestic
Bacteria
LEAD SCIENTIST: Norm Schaad, Ft. Detrick, Maryland
Epidemiology
and Management of Xylella Fastidiosa (XF) and other Exotic and Invasive
Diseases and Insect Pests
LEAD SCIENTIST: Drake Stenger, Parlier, California
Management
of Citrus and Date Genetic Resources and Information
LEAD SCIENTIST: Richard Lee, Riverside, California
Genetic
Improvement of Citrus
LEAD SCIENTIST: Kim Bowman, Fort Pierce, Florida
Domestic,
Exotic, and Emerging Diseases of Citrus, Vegetables, and Ornamentals
(DEED)
LEAD SCIENTIST: Timothy Gottwald, Fort Pierce, Florida
ARS Research Publications on Citrus
Greening/Huanglongbing (HLB)
Publication Abstract:
Effect
of Early Detection Greening on Juice Flavor and Chemistry
Publication Abstract:
NPDN
Citrus Greening Diagnostic and Detection Efforts
Asian
Citrus Psyllid and Citrus Greening - A Closer Look at the Vector
Citrus and Vegetable Magazine
Huanglongbing,
Citrus Greening: Preparing for the Future
Subtropics Newsletter
Twelve
Polymorphic Microsatellite Loci from the Asian Citrus Psyllid, Diaphorina Citri
(Kuwayama), the Vector for Citrus Greening Disease (Huanglongbing)
Molecular Ecology Notes
Sensitivity
Of PCR-based Methods for Detection of Asiatic Strain of the Huanglongbing
Bacterium in Symptomatic and Asymptomatic Citrus Tissues
Proceedings of the Huanglongbing-greening International Workshop, July
14-21, 2006, Ribeiro Preto, Brazil
Publication
Abstract: Differences in Secondary Metabolites in Leaves from Trees Affected
With the Greening (Hlb) Disease
Citrus
Huanglongbing: The Pathogen and Its Impact
Plant Health Progress
Citrus
Canker and Citrus Huanglongbing, Two Exotic Bacterial Diseases Threatening the
Citrus Industries of the Western Hemisphere
Outlooks on Pest Management
Progress
Report to the Citrus Industry: Florida Citrus Plant Protection Committee
(FCPPC)
Citrus Industry
Detection
And Identification of Candidatus Liberobacter Species Associated with Citrus
Huanglongbing by Multiplex Real-time PCR
Journal of Microbiological Methods
Gene
Expression in the Asian Citrus Psyllid: Vector of Citrus Greening (Hemiptera:
Psyllidae)
Joint Proceedings of the 89th Annual meeting and 6th International Caribbean
Conference of the Florida Entomologtical Society
Incidence
Of the Asian Citrus Psyllid, Diaphorina Citri (Hemiptera: Psyllidae) and its
Parasitoid Tamarixia Radiata (Hymenoptera: Eulophidae) in Florida
Citrus
The 91st Annual Meeting of the Florida Entomological Society
Ribosomal
Proteins of the Asian Citrus Psyllid, Diaphornia Citri
National Center for Biotechnology Information (NCBI)
Reovirus-like
Sequences Isolated from Adult Asian Citrus Psyllid, (Hemiptera: Psyllidae:
Diaphorina Citri)
Florida Entomologist
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
Gene
Expression in Citrus Sinensis (L.) Osbeck after Infection with the Bacterial
Pathogen Candidatus Liberibacter Asiaticus Causing Huanglongbing in
Florida
Plant Science
Evaluation
Of DNA Amplification Methods for Improved Detection of Candidatus Liberibacter
Species Associated with Citrus Huanglongbing
Plant Disease
Publication Abstract
Genome
Sequence of Candidatus Liberibacter Asiaticus, the Casual Agent of Citrus
Huanglongbing (Greening)
Effects Of a Particle Film on Biology and Behavior of Diaphorina Citri
(Hemiptera: Psyllidae) and its Infestations in Citrus
Journal of Economic Entomology
Discovery
of a Viral Pathogen in the Asian Citrus Pysllid
72nd Annual Meeting of the Florida Academy of Sciences in conjunction with
the 85th Annual Meeting of the Georgia Academy of Sciences, March 14-15,
Jacksonville, Florida
Daily
Timing of Mating and Age at Reproductive Maturity in Diaphorina Citri
(Hemiptera: Psyllidae)
Florida Entomologist
Optimized
Quantification of Unculturable Candidatus Liberibacter Species Causing Citrus
Huanglongbing in Host Plants by Real-Time PCR
Plant Disease
Publication Abstract:
Genome
Sequence of Candidatus Liberibacter Asiaticus, the Casual Agent of Citrus
Huanglongbing (Greening)
Publication Proceedings:
Concepts
in Huanglongbing Epidemiology
Multiplex
Taqman-based PCR for Sensitive and Accurate Quantification of Citrus HLB and
CVC Pathogens; Candidatus Liberibacter and Xylella Fastidiosa
Proceedings of the Huanglongbing-greening International Workshop
Optimized
Quantification of Unculturable Candidatus Liberibacter Species Causing Citrus
Huanglongbing in Host Plants by Real-Time PCR
Plant Disease
First
Report of Dodder Transmission of Huanglongbing from Naturally Infected Murraya
paniculata to Citrus
Plant Disease
Incidence
of Huanglongbing in Psyllids Under Natural Conditions in Florida
Phytopathology
Preliminary
Spatial Pattern Analysis of Huanglongbing in Sao Paulo, Brazil
International Organization of Citrus Virologists Proceedings
Use
of Psyllids in Early Identification of Huanglongbing Disease of Citrus
Phytopathology
Huanglongbing
Epidemiology: an International Perspective
Proceedings of Huanglongbing-greening International Workshop, July 14-21,
2006, Ribeiro Preto, Brazil
Huanglongbing:
The Dragon Arrives in the USA
Huanglongbing-greening International Workshop, July 14-21,2006, Ribeiro
Preto, Brazil
Epidemiology
of Huanglongbing in Sao Paulo
Huanglongbing-greening International Workshop, July 14-21, 2006, Ribeiro
Preto, Brazil
Huanglongbing
Epidemiology: Tracking the Dragon Through Time and Space
Second International Citrus Canker and Huanglongbing Workshop, Orlando, FL,
November 7-11, 2005
Spatial
Distribution of Huanglongbing Symptomatic Trees in Citrus Groves in Sao Paulo,
Brazil
Second International Citrus Canker and Huanglongbing Workshop, Orlando, FL,
November 7-11, 2005
Detection
Of Candidatus Liberibacter Asiaticus from Citrus Huanglongbing Samples in China
By Nested Conventional and Real-time PCR
Phytopathology
Biology,
History and World Status of Diaphorina Citri
North American Plant Protection Organization Workshop, Taller Internacional
Sobre Huanglongbing y el Psilido Asiatico de los Citricos, del 7 at 9 de Mayo
de 2008, Hermosillo, Sonora
Progress
Towards the Development of an Effective Risk Analysis Process for the Florida
Citrus Nursery Industry to Mitigate the Impact of Citrus Canker and
Huanglongbing
Proceedings from the International Citrus Canker and Huanglongbing Workshop,
Orlando, FL, Nov. 2005
Intercropping
Of Citrus and Guava Trees for Management of Huanglongbing
Florida Entomological Society Annual Meeting, July 15-18, 2007, Sarasota,
Florida
Psyllids
as a Tool in Evaluating the Efficiency of Different Management Practices for
Control of Citrus Huanglongbing Disease
Phytopathology
Novel
Molecular Technique for Rapid Cloning of Unknown Sequences From Unculturable
Huanglongbing (HLB) Associated Bacterium, Candidatus Liberibacter
American Phytopathology Society Meeting
Murraya
paniculata (Orange Jasmine), a Host and Possible Inoculum Reservoir for
Candidatus Liberibacter Asiaticus, Causal Agent of Huanglongbing
Phytopathology
Large-scale
Surveys for Multiple Pest Species; the Search for Citrus Canker and
Huanglongbing in Florida
American Phytopathological Society Annual Meeting
Comparative
Genomics and Phylogenetic Analyses of Newly Cloned Genomic Regions From the
Citrus Huanglongbing (HLB)-associated Bacterium Candidatus Liberibacter
American Phytopathology Society
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