ASHS 2025 Conference

Citrus is one of the most widely grown fruit crops worldwide with a total of $2.98 billion in productivity in the U.S. However, the citrus industry has been significantly affected by Huanglongbing (HLB) which caused as much as 90% production loss in Florida. Efficient phenotyping and data management will aid breeding selection and hasten the development of high yielding citrus varieties with durable resistance to HLB. The Citrus Genome Database (CGD, www.citrusgenomedb.org), an integrated web-based community database for citrus genomic, genetic, and breeding research, offers the Breeding Information and Management System (BIMS) for efficient public or private data management. BIMS is compatible with Field Book, an Android app which allows breeders to collect data on phones or tablets. In addition, the compliance of BIMS and Field Book with the Breeding API (BrAPI) enables seamless data transfer between them. This transition to electronic data collection and data management using BIMS has boosted the efficiency of the University of Florida citrus breeding program. Under the 2022-funded SCRI-project ‘Advanced National Database Resources for Specialty Crop Research and Improvement’, we aim to collaborate with citrus breeding programs across the U.S., offering in-person or webinar training on BIMS and Field Book, while sharing updates on these tools with citrus breeders.

Nutrient availability is an essential aspect of plant growth and development. Sandy soils have low nutrient-holding capacities. Huanglongbing (HLB) trees have lower fine root density and thus decreased capacity to uptake nutrients. Organic amendments have been known to increase nutrient-holding capacities in sandy soils and provide additional nutrients. The objectives of this study were to 1) determine the influences of organic amendments on citrus production on sandy soil, and 2) assess the potential of organic amendments to alleviate the negative impacts of HLB. The study was conducted over six months in a greenhouse setting at the Citrus Research and Education Center in Lake Alfred Florida using Valenica sweet orange on Swingle citrumelo rootstock grown on Candler fine sand. Treatments of compost (5% and 10% by volume) and peat moss (5 and 10% by volume) and a control composed of Candler fine sand without amendment were applied to a total of 50 trees, 25 of which were HLB-affected and the other 25 were healthy trees. The following variables were measured: tree diameter, tree height, leaf chlorophyll content, soil nutrient content, tissue nutrient content, soil organic matter content, and biomass and nutrient accumulation. Organic amendments improved soil organic matter content by 20 to 40%. Organic amendments also increased plant and root growth parameters and demonstrate an ability to alleviate the negative impacts of HLB. Our research will eventually be followed up by field studies to validate the greenhouse observations.

Huanglongbing (HLB), or citrus greening, has severely impacted citrus production in Florida, with no known cure currently available. Growers have increasingly adopted soil-focused management strategies, including cover cropping, to improve soil health and support tree resilience. In the Indian River District, where sandy soils with low fertility and organic matter prevail, the potential for cover crops to influence the soil microbiome remains underexplored. To investigate this, a three-year field trial was established in collaboration with a commercial grower and the University of Florida, IFAS, Indian River Research and Education Center, in Ft. Pierce. The trial included ‘Star Ruby’ grapefruit trees grafted on ‘US-942’, ‘Bearss’ lemon trees grafted on ‘Sour Orange’, and ‘OLL’ sweet orange trees grafted on ‘US-942’ rootstock. A randomized complete block design was used to compare conventional management (no cover crops) to a cover crop system, with species planted biannually and terminated at the end of each season. Soil microbiome composition and diversity were assessed seasonally through high-throughput sequencing, alongside measurements of soil nutrients, organic matter, moisture, and temperature. Early results suggest that the use of cover crops may influence soil microbial communities, with some differences observed between treatments over the three-year period. These include modest shifts in microbial diversity and structure, although the functional significance of these changes remains unclear. These findings suggest that cover crops may influence the soil microbiome in HLB-affected citrus groves, potentially contributing to improved soil conditions and offering a possible strategy to support long-term sustainability in southeast Florida citrus production systems.

Fruit retention is a critical factor for citrus growers, as fruit that remains on the tree to be harvested is the fruit that gets paid for. The challenge has been exacerbated by Huanglongbing (HLB), a disease that significantly increases premature fruit drop, making it essential to identify the key factors influencing fruit retention. In this study, the relationship between fruit size, leaf count, seed viability, and fruit detachment force (FDF) was investigated to better understand what contributes to fruit retention on the tree. A total of 30 fruit per tree in four trees were tagged,fruit size and leaf count on the fruiting branch were recorded and monitored over five weeks., In the second week, Ethephon (150 ppm) was sprayed to induce faster fruit drop. Weekly measurements were taken to track fruit drop. At the end of the study period, the remaining fruit were removed along with their stems to measure FDF, viable seed count, and aborted seed count. The findings indicate a positive correlation between the fruit’s FDF and leaf count, suggesting that fruit with more supporting foliage are more likely to remain attached. Additionally, a negative correlation between the number of aborted seeds and FDF was observed, implying that fruit with more aborted seeds are also more susceptible to detachment. These findings were strengthened by comparing the average values of leaves and aborted seeds between the fruit that had to be manually removed and the fruit that dropped prematurely. The prematurely dropped fruit had a significantly lower number of leaves (9 vs. 16.4 average) and a higher aborted seed number (1.9 vs. 0.9 average). These insights should motivate growers to find therapies that promote leaf growth for a more profitable orchard. The study also points to a need for further investigation into the causes of seed abortion to get a clearer picture of the basic mechanism causing HLB-induced fruit drop.

Huanglongbing (HLB), associated with Candidatus Liberibacter asiaticus (CLas), continues to devastate citrus production worldwide. Individual protective covers (IPCs) offer a physical barrier against the Asian citrus psyllid, delaying CLas infection in young trees. However, once removed, trees become vulnerable to rapid infection. This study evaluates an integrated approach utilizing IPCs followed by systemic oxytetracycline (OTC) trunk injections to mitigate disease progression and sustain tree health. A field trial was established with ‘Valencia’ sweet orange (Citrus sinensis) grafted onto US-812 or US-942 rootstocks. Trees were either protected with IPCs for 18 months after planting (“late infected”) or had “open” IPCs (“early infected”). All trees received annual OTC injections in 2023 and 2024, beginning 10 months after IPC removal. CLas titers, OTC residues, tree growth, fruit yield and quality, leaf nutrient content, and root endorhizosphere microbial dynamics were assessed. Results indicate that IPCs successfully delayed infection, as late-infected trees maintained lower CLas titers for the first five months after IPC removal and exhibited denser canopies and larger scion and rootstock trunk diameters than early-infected trees. OTC injections significantly reduced CLas titers in leaves, with effects persisting for up to six months. However, no significant reductions in CLas titers were detected in fibrous roots, suggesting limited OTC translocation to the root system. Injected trees exhibited a greener canopy color, greater leaf size, higher chlorophyll content, higher yield, larger fruit size, and better juice quality compared to non-injected trees. No significant changes in leaf nutrient content were observed, and the root endorhizosphere microbial diversity remained unchanged across treatments, indicating minimal disruption to the microbial community due to the antibiotic. These findings provide evidence supporting the combination of IPCs and systemic delivery of OTC as an integrated strategy to manage HLB in new citrus plantings. IPCs delay the onset of infection, allowing trees to establish a healthy canopy and robust root system, while OTC injections aid in sustaining tree health post-infection. The integration of these practices provides a promising framework for establishing productive citrus orchards under HLB-endemic conditions.

Huanglongbing (HLB), associated with phloem-limited bacteria Candidatus Liberibacter asiaticus (CLas), is a major threat to citrus production worldwide, severely reducing tree health, yield, and fruit quality. In Florida, trunk injection of oxytetracycline (OTC) has emerged as a promising management strategy for HLB. Under this context, this study aimed to enhance the efficacy of OTC injection by evaluating different injection volumes, modes of injection (one or two-sided), and injection timing in HLB-affected ‘Valencia’ orange (Citrus sinensis) trees in southwest Florida. Two experiments were conducted with 8-year-old trees. The first experiment, implemented in two locations, assessed four combinations of different OTC volumes and modes of injection: 1) 50 mL (one-sided), 2) 100 mL (one-sided), 3) 100 mL (two-sided, 50 mL each side), and 4) 200 mL (two-sided, 100 mL each side), all delivering 0.825 g (a.i.) OTC (Rectify, AgroSource, Inc.) per tree. The second experiment compared early (May) and late (July) injections using 100 mL (two-sided, 50 mL each side), delivering 0.825 g (a.i.) OTC (Rectify) per tree. Injectors were placed on opposite sides of the trunk for the two-sided treatments. OTC solutions were prepared right before injection. In both experiments, treatments were compared against an untreated control. The experimental design was completely randomized, with 10 single-tree replications for the first experiment and 8 replications of 4 trees each for the second. Leaf samples were collected over time to analyze bacterial (CLas) titers and OTC residues, while canopy health, yield, and fruit quality were evaluated annually. For the second experiment, fruit development (size and peel color) was monitored monthly after OTC injection, and fruit yield and quality were assessed annually. Our results demonstrate that two-sided injection increases fruit yield more than one-sided injection and that the combination of two-sided injection and a larger volume of the injected solution may further enhance fruit yield compared to the untreated control. This improvement is attributed to better OTC distribution within the canopy, leading to greater bacterial suppression and tree recovery. Moreover, early (May) injection promotes fruit size by extending the fruit growth period, while late (July) injection enhances juice soluble solids content with a more compact fruit size. However, early injections result in greener fruit, which requires a longer maturation period to achieve the desired peel color and sugar content. These findings offer valuable insights for optimizing OTC trunk injection strategies to improve citrus health and productivity in HLB-affected citrus orchards.

The combined use of Individual Protective Covers (IPCs) and oxytetracycline (OTC) trunk injection offers a promising strategy for managing huanglongbing (HLB) in young citrus trees by reducing environmental stress and preventing Candidatus Liberibacter asiaticus (CLas) inoculation. This study evaluated whether young citrus trees that were grown without IPCs for the first two years after planting and severely affected by HLB can be rehabilitated by OTC injections, and whether IPCs provide additional benefits beyond OTC alone. ‘Valencia’ sweet orange trees on US-812 and US-942 rootstocks, were organized in a randomized complete block design with three treatments: 1) no injection no IPC, 2) OTC injection no IPC, and 3) OTC injection IPC. Each treatment-rootstock combination consisted of 14 single-tree replications. Trunk injections were performed annually for two years (2023-2024) using Chemjet tree injectors, with solutions delivered into the rootstock. Comprehensive data were collected on the yield, juice quality, bacterial titers, disease state, flushing patterns, and psyllid infestation. No significant differences were observed between the rootstocks except for the juice quality, which was better in combination with US-812. OTC-injected trees consistently exhibited higher yields and improved juice quality, with no additional benefits from IPCs. A significant decrease in CLas titers was noted starting three months post-injection. Injected trees under IPCs had fewer HLB symptoms in the second year, and injected trees exhibited a significant increase in canopy density compared with non-injected trees. Trees with IPCs flushed less frequently during summer and winter than trees without IPCs. The psyllid infestation rate was the same in injected and non-injected trees, indicating that OTC treatment does not affect host attractiveness. These findings highlight the potential of OTC trunk injection to rehabilitate young HLB-affected citrus trees and enhance tree productivity. The longer-term role of IPCs in young tree rehabilitation is still under investigation.

The systemic delivery of oxytetracycline (OTC) by trunk injection has emerged as a viable strategy to diminish the impacts of the bacterial disease Huanglongbing (HLB) in Florida. This study aimed to determine the optimal OTC dose and best time of delivery to enhance tree health and productivity in mature HLB-affected citrus trees. It also investigated whether OTC effects persist after one single injection compared to two consecutive annual injections. The study began in 2023 at a commercial citrus grove in Polk County, Florida, using 18-year-old ‘Valencia’ (Citrus sinensis) trees grafted onto Swingle (C. paradisi × Poncirus trifoliata) rootstock. Four OTC doses (0.55 g, 0.825 g, 1.1 g, and 1.65 g of active ingredient per tree) were evaluated alongside two application times, spring and late summer, with a non-injected control for comparison. The experiment was a randomized complete block design with eight replications containing four trees. A commercial OTC formulation (ReMedium TI, 95% oxytetracycline hydrochloride) registered in Florida was applied using commercial tree injectors (FlexInject). Doses were applied in 100 ml acidified water through a single injector, except for the highest dose, which was split between two injectors and applied in a volume of 75 ml on opposite sides of the trunk. All trees received their designated doses in year 1, except for the non-injected controls. Only half of the trees injected in year 1 received a second dose in year 2. Trees were harvested in March 2024 and February 2025. Fruits were collected for fruit and juice quality analysis and to determine OTC fruit residue levels. Regardless of the dose, all OTC-treated trees produced more, larger-sized fruits, more total soluble solids (TSS), and a higher TSS-to-acid ratio compared to non-injected controls. The best results were obtained with the highest dose applied by split injections. There were no major differences between spring and summer injections except for the TSS content, which was higher and the percent acid, which was lower when trees were injected in late summer. However, fruit OTC residues were above the allowed maximum after late summer injections, suggesting that injections should be completed by the end of spring. Trees injected for two consecutive years produced significantly more, better-quality fruits than trees injected only once in the first year. These results confirm the efficacy of OTC trunk injections to enhance productivity and fruit quality under HLB-endemic conditions and provide important guidelines regarding dose and timing of injections.

Citrus production in the State of Florida has been decimated by the disease Huanglongbing (HLB). This disease is associated with the phloem-limited, gram-negative bacteria Candidatus Liberibacter asiaticus (CLas) and is vectored by the Asian citrus psyllid (Diaphorina Citri). Since HLB was first identified in Florida in 2005 it spread rapidly and was considered endemic in the state by 2013, resulting in a nearly 90% decline in citrus fruit production. While breeding more tolerant or fully resistant cultivars is likely the best long-term solution, trunk injections of the antibiotic oxytetracycline were granted emergency use approval in October 2022 to combat the bacteria. Historically most of Florida’s citrus production has been sweet orange (Citrus sinensis (L.) Osbeck) cultivars including ‘Hamlin’ and ‘Valencia’ which were primarily destined for juice processing. Unfortunately, all known commercial sweet orange cultivars are susceptible to HLB infection leading to the rapid and drastic decrease in production across the state. Of the sweet orange cultivars that have been released by the University of Florida Institute of Food and Agricultural Sciences (UF-IFAS), Orie and Louise Lee (‘OLL’) lines have shown some degree of tolerance to HLB in cultivar field trials. In our experiment we evaluated the effects of rootstock selection and oxytetracycline (OTC) trunk injections on the fruit and juice quality of the ‘OLL-8’ sweet orange scion. Three of the evaluated rootstocks (‘US-942’, ‘US-897’, and ‘Swingle’) are industry standard diploids, while the other three rootstocks (‘UFR-2’, ‘UFR-4’, and ‘UFR-6’) are tetraploids released by the University of Florida. For each of these rootstocks there were trees that were injected with OTC and untreated control trees. Fruit were harvested at several time points and data were collected on juice quality attributes including titratable acidity in citric acid equivalents, total soluble solids, sugar/acid ratio, pounds-solids per box, and juice color, as well as fruit characteristics including mass, diameter, total yield, and premature fruit drop. The trees that were injected with OTC had significantly larger mean fruit diameter, higher mean ratio, and lower premature fruit drop than untreated controls. There was also evidence for statistically significant differences among rootstock selections in conjunction with the ‘OLL-8’ scion for each of the characteristics that were evaluated. These results indicate that rootstock selection and OTC-trunk injections can significantly improve fruit and juice quality of the ‘OLL-8’ sweet orange scion. However, more research is needed on the effects of OTC injections in different rootstock-scion combinations.

Citrus Huanglongbing (HLB), also known as citrus greening, is associated with Candidatus Liberibacter asiaticus (CLas), a phloem-limited bacterium transmitted by an insect vector, Asian Citrus Psyllid (ACP). Currently, there are no commercially viable treatment options available for HLB management. Trunk injection of Oxytetracycline (OTC) has been widely adopted as a treatment option in Florida. Currently, OTC is not approved for use in Texas citrus, and no OTC efficacy data is available. This study evaluated the efficacy of OTC in mitigating HLB and managing tree health in nine and 17-year old ‘Rio Red’ grapefruit (Citrus paradisi Macfadyen) trees on sour orange (Citrus aurantium L.) rootstock, on a randomized complete block design in two commercial orchards. RECTIFY™ (95% Oxytetracycline hydrochloride) was injected into tree trunks at two rates (0.55g and 1.1g per tree) using Chemjet® tree injectors during June-July 2023 and May 2024. Trees were evaluated for various attributes, including periodic (pre-treatment, three, six, and nine months after OTC injection) bacterial titer in leaf and root tissues and tree health monitoring (canopy color, canopy density, and HLB severity) for the same time intervals. Fruits collected at harvest maturity were evaluated for yield, fruit size, and juice quality (brix, titratable acidity, flavonoids, carotenoids). Additionally, pre-harvest fruit drop and trunk injection site damage were recorded. OTC residue was measured in whole fruit and juice using Ultra-High-Performance Liquid Chromatography coupled with tandem Mass Spectrometry (UHPLC-MS-TOF). Nine-year-old trees treated with 1.1g of OTC/tree in one of the sites showed a significant reduction of bacterial titers in leaf tissue. OTC treatment did not significantly improve yield. Canopy color showed noticeable improvement after the second OTC injection in the sites, whereas canopy density remained largely unaffected. After the second OTC injection, HLB severity and pre-harvest fruit drop were reduced, and improvement in fruit size was observed in 9-year-old trees. There is no significant improvement in juice quality. Damage caused by trunk injections healed rapidly in older trees than in younger trees. No OTC residue was detected in the juice and whole fruit at six months after the OTC injection. This is the first report on the efficacy of OTC for HLB management in Rio Red grapefruit in South Texas.

Huanglongbing (HLB, aka citrus greening) has devastated citrus production around the world, especially in Florida where the disease has been endemic since 2013. HLB is associated with phloem-limited bacteria, Candidatus Liberibacter asiaticus, vectored by the Asian citrus psyllid, Diaphorina citri. Elimination of the disease vector is difficult because of its abundance and the high costs of frequent insecticide applications. Foliar applied therapies to treat infected trees are largely ineffective because of the systemic distribution of the bacteria. Trunk injection of oxytetracycline (OTC) has emerged as a possible therapy to systemically deliver and target the pathogen and restore tree health. Since the registration of trunk injection of OTC for commercial use in Florida, our lab has conducted numerous field studies to assess the efficacy of this therapy on a large scale and study the influence of various factors such as tree age, rootstock, OTC dose, and time and method of application. Overall, all studies revealed significant improvements in fruit production along with increases in fruit and juice quality after one year of application. Yield improvements after two years of application were cumulative, reaching up to two-fold or more. The magnitude of improvements depended on various factors. Young trees generally responded better than older trees, and tree responses varied based on the rootstock. The efficacy of the therapy also depended on the dose of OTC administered to the trees, with higher doses generally generating larger effects. Moreover, delivering OTC on multiple sides of a tree instead of on only one side enhanced its distribution and therefore, efficacy. Late season injections improved the juice quality more but increased the OTC residue content in the fruits. The currently allowed residue level is 10 ppb, which was not exceeded when injections occurred in spring or early summer. OTC is phytotoxic and can have adverse effects on the tree. Efforts are underway to reduce or eliminate these negative effects and improve efficacy. Alternative therapies to be used instead of, or in combination with OTC, are also under evaluation. Taken together, the systemic delivery of OTC by trunk injection has emerged as a viable and economically feasible therapy to manage HLB in Florida and has been widely adopted. Nevertheless, it is regarded as a short-term solution until other solutions become available.

In Florida and worldwide, citrus production is threatened by Huanglongbing (HLB), associated with phloem-limited Candidatus Liberibacter asiaticus (CLas). Oxytetracycline delivery by trunk injection has been approved to treat commercial citrus groves affected by this endemic disease. However, the commercially available formulations require acidification of the active ingredient (oxytetracycline hydrochloride, OTC) to a pH of 1.8-2.0 to dissolve and stabilize the antibiotic, which may cause trunk damage, chloride toxicity, and limits compatibility with other compounds. A novel adjuvant has been developed, using EPA-approved ingredients to dissolve and stabilize OTC at a neutral pH while maintaining efficacy. This study compares the efficacy of neutralized and acidified solutions of OTC with and without the addition of ZnSO4 to optimize HLB management. The efficacy of Streptomycin (STM) as an alternative to or combined with OTC was also assessed. A field trial was conducted in a commercial citrus orchard in southwest Florida using seven-year-old ‘Valencia’ sweet orange trees grafted on X-639 rootstock. The experimental design was a randomized block with ten treatments and eight replications, each containing four trees. Treatments included combinations of OTC, STM, and ZnSO4 with or without the adjuvant, and appropriate controls. Trees were injected in June 2024 with 100 mL of treatment solution on one side of the trunk using commercial (FlexInject, TJ BioTech) injectors. Leaves were collected to assess CLas titers and bacterial suppression. Phytotoxic effects in the canopy and trunk damage at the injection site were evaluated. Treatments containing the adjuvant and/or OTC caused significant phytotoxicity and more trunk damage. Trees were harvested in March 2025. Fruit yield was higher for all treatments containing OTC compared to the controls . The highest yield was measured when trees were injected with a combination of OTC and STM. The findings of this study led to the redesign of the neutral pH adjuvant to minimize tree damage and enhance OTC efficacy. The optimized formulation will be tested using the same experimental design in upcoming studies.