Horticultural & Management

Reducing fruit drop by altering hormonal responses within the tree through nutritional and hormonal therapies: a mechanistic affordable approach

Determining best timing for Brassinosteroid (Brs) application to achieve maximum beneficial effects on citrus tree health and fruit yield and quality

Directed Research Solicitation: Evaluating different rates of oxytetracycline administered by trunk injection in mature sweet orange trees

Testing the injection of oxytetracycline (OTC) in a pH neutral solution

Determine optimal timing for application of fertilizer to improve fruit quality and reduce preharvest drop

OTC Directed Research Solicitation: Use of CRDF Rootstock Trial Locations for Testing Bactericides Inserted into Trees Through Systemic Delivery Devices

Organic acids compared to conventional acidification for improved nutrient uptake and root physiology

1. Please state project objectives and what work was done this quarter to address them:

Objective 1: Determine effects of lowered soil pH on CLas populations and root physiology including internal root apoplast and vascular tissue pH.
We got our experiment in rhizotrons completed in September 2023. Sample processing and data analysis is under way. Root tracing and quantification of root traits will be completed in the next quarter. We should get the data processed and published in the next quarter or immediately following project completion.

Objective 2: Field test multiple acidification materials including organic acids for tree response CLas suppression, nutrient uptake, and root and vascular pH changes. In this quarter, we continued root sampling and soil pH determinations and applied final round of the treatments. We also finalized canopy determinatiions for trees used for the study.

2. Please state what work is anticipated for next quarter:
We will collect fruit yield and juice quality data in March/April 2024 to finalize objective 2 milestones.
We will get one article prepared and published in a refereed journal.

3. Please state budget status (underspend or overspend, and why):

The budget is on track and meeting the project milestones.

Management of tree health and huanglongbing disease pressure using advanced Zn formulations

Integrated management of sting nematode in newly planted citrus trees

Integrated management of sting nematode in newly planted citrus trees

Right Leaf Sampling-The first and most critical step to good nutrition program

Breaking the Diaprepes Life Cycle

Organic acids compared to conventional acidification for improved nutrient uptake and root physiology

Recent work demonstrated that irrigation and soil acidification can improve the health and productivity of huanglongbing (HLB)-affected citrus; however, the best long-term methods to achieve this response have not been investigated. This work was done on highly pH-sensitive rootstocks, so the mechanism and broader applicability to other rootstocks is not fully understood. pH adjustment with sulfuric acid or sulfur treatment does temporarily modify the pH, but other acidifiers such as organic acids could provide additional benefits while acidifying the soil. The purpose of this project was to understand the physiological response of HLB-affected roots to soil acidification and to determine if organic acids that also provide improvement in soil health can effectively acidify the root zone and improve nutrient uptake and tree productivity through two main objectives.
Objective 1. Determine effects of lowered soil pH on Candidatus Liberibacter asiaticus (CLas) populations and root physiology including internal root apoplast and vascular tissue pH. Large-scale field trials of acidification on different rootstocks would require long-term experiments with carefully laid out plantings of multiple rootstocks at multiple sites with an overlaid acidification treatment. Understanding how acidification affects HLB-affected root physiology and CLas populations in pH-sensitive and tolerant rootstocks could speed up recommendations for acidification on new rootstocks.
Objective 2. Field test multiple acidification materials including organic acids for tree response, CLas suppression, nutrient uptake, and root and vascular pH changes. Organic acids provide multiple benefits to soil and root health that sulfur-based acidification cannot provide. If these acidifiers can provide the same acidification benefit, it would increase growers’ toolset of recommended acidification treatments and provide additional benefits to grove management in nutrient uptake and soil health.
This project addressed priority 2 of the RFP, specifically whether lower soil pH lowers internal root pH and subsequently lowers bacteria levels in the tree and if using organic acids for acidification can increase root nutrient uptake. Key findings from the greenhouse study were that acidic soils stimulate root growth, particularly around pH 5.5 conditions; citrus roots exhibit remarkable resilience and internal compensation mechanisms in response to pH variations. Optimizing soil pH and nutrient management can mitigate the impacts of HLB and promote the resilience of citrus trees. The field study showed a positive correlation between soil pH and soil calcium (Ca), magnesium (Mg0, zinc (Zn), manganese (Mn), and boron (B), possibly suggesting that the availability of these soil nutrients increased as pH increased. A negative correlation was observed between soil pH and soil iron (Fe), sulfur (S), potassium (K), and phosphorus (P), indicating decreased nutrients in soil solution as pH increased. There was no significant canopy difference between treatments but a difference between time points due to trees deteriorating due to the bacteria or loss caused by natural hazards, especially in hurricane-prone Florida. Results show no significant difference in fruit yield and fruit quality parameters in all treatments. In both sites, soil pH positively correlated to soluble solids and soluble solids to acid ratio but negatively to titratable acidity.

Project Outputs and Presentations
Journal manuscripts in preparation or accepted
1) Sambani, D., T. Vashisth, D. Bright, D. Kadyampakeni. In preparation. Physiological responses of huanglongbing (HLB)-affected citrus tree roots to soil acidification. Journal of Environmental Quality.
2) Sambani, D., T. Vashisth, D. Bright, H. Ghoveisi, L. Rossi, T. Ayankojo, A. Atta, D. Kadyampakeni. The impact of organic acids on soil health and acidification for enhanced nutrient uptake and tree productivity in HLB-affected citrus trees. HortScience (In review)
3) Sambani, D. and Kadyampakeni, D. Exploring the Nexus of Citrus HLB Dynamics and Interactive Influences of Soil Nutrient Availability: A Comprehensive Review. Journal of Plant Nutrition (accepted).
4) Kadyampakeni, D., T. Vashisth, D. Sambani. 2024. Soil fertility and soil pH interaction. Citrus Industry Tip of the Week article, Aug. 2024.
5) Kadyampakeni, D. and T. Vashisth. In preparation. Interaction of soil pH and soil fertility. EDIS Publication.

Conference Proceedings/Presentations
1) Sambani, D., T. Vashisth, L. Rossi, and D. Kadyampakeni. 2024. The physiological responses of citrus tree roots to soil acidification. SSSA 2024 Bouyoucos Summer Conference, June 10-12, 2024, San Juan, Puerto Rico.
2) Sambani, D., T. Vashisth and D. Kadyampakeni. 2023. The physiological responses of citrus tree roots to soil acidification. Poster presentation ASA/CSSA/SSSA Tri-Society Meetings, St. Louis, Missouri. Oct. 29-Nov. 1, 2023.
3) Sambani, D., T. Vashisth and D. Kadyampakeni. 2023. The physiological responses of citrus tree roots to soil acidification. ASHS Poster Presentation, Orlando, FL. July 31-Aug. 4, 2023.
4) Sambani, D., T. Vashisth, L. Rossi and D. Kadyampakeni. 2023. The physiological responses of HLB-affected citrus tree roots to soil acidification. Southern Fruitworkers Conference, Quincy, FL. November 14-16, 2023.
5) Sambani, D., T. Vashisth, L. Rossi and D. Kadyampakeni. 2024. The physiological responses of HLB-affected citrus tree roots to soil acidification. 9th UF Water Institute Biennial Symposium, Gainesville, FL. Feb. 20-22, 2024.
6) Sambani, D., T. Vashisth and D. Kadyampakeni. 2023. The physiological responses of citrus tree roots to soil acidification. FSHS Oral Presentation, Daytona Beach, FL. June 11-13, 2023.

Acknowledgments
The researchers are grateful to the support of the Citrus Research and Development Foundation for funding this research.

Directed Research Solicitation: Evaluating different rates of oxytetracycline administered by trunk injection in mature sweet orange trees

1. Please state project objectives and what work was done this quarter to address them: Objective 1: To compare different rates and annual use patterns of trunk-injected OTC on late-season (Valencia) and early-season (Hamlin) sweet orange tree and their effects on health, yield, and fruit quality over a period of 3 years in a commercial citrus production environment.Year-2 injections were completed in May for the Hamlins and in June for the Valencias. Tree size and canopy volume data were collected.  Leaf samples were collected for CLas analysis.  Obective 2: To compare spring with late summer injections in Valencia orange trees to determine if OTC effects on yield can be enhanced, and the harvest window extended, through timing of injections.Valencia OTC fruit residue analyses were completed. Fruit from trees injected in June 2023 had residues below the allowed 10 ppb regardless of the rate. Fruit from trees injected in September had higher residues, suggesting that trees should not be injected in September. This year’s late summer injections will therefore be conducted in August instead of September.    2. Please state what work is anticipated for next quarter: We are preparing for the Valencia August injections. Leaf sampling will be conducted for CLas analysis. Phytopthora trunk rot has been observed in this location. The rot does not seem to be associated with OTC injections; we will conduct measurements/ratings to document this. 3. Please state budget status (underspend or overspend, and why):The budget is as expected.