USDA-ARS Characterizing the Effect of Environmental Variables on Candidatus Liberibacter asiaticus in Citrus
*Applications are reviewed on a rolling-basis.
ARS Office/Lab and Location: A research opportunity is currently available with the U.S. Department of Agriculture (USDA), Agricultural Research Service (ARS), located in Fort Pierce, Florida.
The Agricultural Research Service (ARS) is the U.S. Department of Agriculture's chief scientific in-house research agency with a mission to find solutions to agricultural problems that affect Americans every day from field to table. ARS will deliver cutting-edge, scientific tools and innovative solutions for American farmers, producers, industry, and communities to support the nourishment and well-being of all people; sustain our nation’s agroecosystems and natural resources; and ensure the economic competitiveness and excellence of our agriculture. The vision of the agency is to provide global leadership in agricultural discoveries through scientific excellence.
The USDA’s Horticultural Research Laboratory (USHRL) located in Fort Pierce, Florida is internationally recognized for its citrus, vegetable, and strawberry research. It is in close proximity to one of the largest citrus, vegetable and strawberry production growing regions in the U.S. Extensive greenhouse, laboratory resources and scientific equipment are available at this facility, while the USHRLs Picos Farm provides nearly 20 acres of farmland for citrus and vegetable pathology research.
Research Project: Citrus greening disease, also known as Huanglongbing (HLB), is one of the most destructive diseases affecting citrus production in Florida and worldwide. The disease is associated with the phloem-limited bacterium ‘Candidatus Liberibacter asiaticus’(CLas), which disrupts carbohydrate transport within the plant, leading to leaf mottling, fruit drop, reduced fruit quality, and eventual tree decline and death. Since its detection in major citrus-producing regions, greening has caused substantial economic losses and poses a continuing threat to the sustainability of the citrus industry, particularly true in Florida.
Management of citrus greening remains challenging due to the lack of curative treatments and the complex interactions among the pathogen, its insect vector (Diaphorina citri, the Asian citrus psyllid), and the host plant. Current control strategies primarily rely on vector suppression, removal of infected trees, and the use of somewhat tolerant rootstocks or scion varieties. However, these approaches are costly, often only partially effective, and sometimes challenging to implement consistently at a commercial scale. As a result, determining regions that may favor plant health (such as cold hardy citrus production areas) may allow a basis for sustainable citrus production in the era of greening. To this end there is a critical need to better understand environmental factors that influence pathogen survival and disease progression.
Temperature is known to play a significant role in the biology of Candidatus Liberibacter asiaticus, affecting its replication, distribution within the host, and symptom expression. Colder weather conditions may reduce greening incidence or slow disease development in certain citrus-growing regions, such as northern Florida and southern Georgia, and parts of California. However, the mechanisms underlying these observations are not understood, and field-based studies are often confounded by variability in weather, host physiology, and vector activity. In particular, the direct effects of cold exposure on pathogen survival within citrus tissues have not been systematically investigated.
The project will implement controlled environment studies to isolate and quantify the impact of low-temperature stress on CLas survival within infected citrus plants. By precisely regulating temperature, duration of exposure, and plant developmental stage, the studies will provide critical insights into the thermal sensitivity of the pathogen independent of vector dynamics. Pathogen quantification will be via qPCR. Understanding how cold temperatures influence CLas persistence and viability within citrus hosts may inform region-specific disease management strategies, improve predictive models of disease spread, and contribute to the development of integrated approaches for mitigating the impact of citrus greening. The findings from this research will help advance knowledge of greening epidemiology and may identify temperature thresholds that could be leveraged in disease management and production planning, including identifying regions more favorable to the host, and less favorable to the pathogen reproduction and survival.
Learning Objectives: Under the guidance of a mentor, the participant will:
- Gain experience conducting independent research projects (with mentoring).
- Develop expertise in a specific plant pathosystem that can be applied to develop hypotheses, and eventually translate this skill to other systems after completion of the project.
- Develop and apply new skills in experiment design and research (e.g., application of molecular methods, statistical analysis).
- Experience in how to actively contribute to a research project and obtain results that will answer to the hypotheses.
- Data analysis and scientific writing that can also be applied in the future.
Mentor(s): The mentor for this opportunity is Clive Bock (clive.bock@usda.gov). If you have questions about the nature of the research, please contact the mentor(s).
Anticipated Appointment Start Date: March 9, 2026. Start date is flexible and will depend on a variety of factors.
Appointment Length: The appointment will initially be for one year, but may be renewed upon recommendation of ARS and is contingent on the availability of funds.
Level of Participation: The appointment is full time.
Participant Stipend: The participant will receive a monthly stipend commensurate with educational level and experience. The anticipated stipend range is $6,600 to $7,000 monthly.
Citizenship Requirements: This opportunity is available to U.S. citizens only.
ORISE Information: This program, administered by ORAU through its contract with the U.S. Department of Energy (DOE) to manage the Oak Ridge Institute for Science and Education (ORISE), was established through an interagency agreement between DOE and ARS. Participants do not become employees of USDA, ARS, DOE or the program administrator, and there are no employment-related benefits. Proof of health insurance is required for participation in this program. Health insurance can be obtained through ORISE.
Questions: Please visit our Program Website. After reading, if you have additional questions about the application process, please email ORISE.ARS.Southeast@orau.org and include the reference code for this opportunity.
Qualifications
The qualified candidate should be currently pursuing or have received a doctoral degree in the one of the relevant fields. Degree must have been received within the past six months, or anticipated to be received by 8/16/2026.
Preferred Skills:
- Some experience of molecular methods (PCR, qPCR etc).
- Experience of plant culture.
- Published articles (e.g., from their dissertation) demonstrating the desired skill set in plant pathology, epidemiology, molecular methods, experimental design and data analysis (and or related branches of science).
- Ability to perform independently and as part of an interdisciplinary team, with strong written, verbal and interpersonal communication skills.
- Some proficiency in MS Word, Excel and PowerPoint and data analysis.
- Familiarity of plant pathology.
- Experience in plant disease epidemiology and molecular biology (or related disciplines).
Stipend
$6,600.00 – $7,000.00 Monthly
Point of Contact
Eligibility Requirements
- Citizenship: U.S. Citizen Only
- Degree: Doctoral Degree received within the last 6 months or anticipated to be received by 8/16/2026 12:00:00 AM.