ASHS 2024 Conference

Background: Florida’s Citrus industry has been devastated by the bacterial disease, Huanglongbing (HLB) (Candidatus Liberibacter asiaticus). The vector of the disease is the Asian Citrus Psyllid (Diaphorina citri). HLB is not just a problem in Florida but affects other citrus-growing areas across the United States. Many homeowner citrus trees already have HLB or have succumbed to the disease. Often, young trees are purchased and decline before they have harvestable fruit. Many homeowners, not educated on the disease, have become disenchanted with attempting to grow citrus. Although no citrus is resistant to HLB, there are tolerant varieties. Objective: Engage Highlands County residents to grow citrus in their yards by offering classes on the proper use of cultural practices to successfully maintain a tree that would supply quality fruit for a longer duration. Introduce them to HLB-tolerant trees and other innovations. Method: Lecture using a two-hour PowerPoint on growing citrus. Teach participants how to identify HLB and other common citrus pests and diseases. Give them a better understanding of citrus nutrition, soil health, and irrigation practices. Introduce them to Individual Protective Covers (IPCs) that can exclude Asian Citrus Psyllids from reaching their trees. Send them home with the knowledge to grow successful citrus at home. Conclusion: In 2023 and 2024, 112 participants attended the Growing Citrus at Home program. Of this, 92 trees were taken home each with an IPC. Seventy-five class participants took a pre- and post-assessment to ascertain knowledge gain. Knowledge gain based on a 10-question pre-and post-assessment went from 36% to 68% which calculates to be an increase of 89 %. pests and diseases. Give them a better understanding of citrus nutrition, soil health, and irrigation practices. Introduce them to Individual Protective Covers (IPCs) that can exclude Asian Citrus Psyllids from reaching their trees. Send them home with the knowledge to grow successful citrus at home. Conclusion: In 2023 and 2024 112 participants attended the Growing Citrus at Home program.

Optimal nutrient management improves the performance of citrus trees affected by Huanglongbing (HLB) in Florida. Current research suggests that HLB-affected trees may require higher levels of micronutrients than those typically recommended for citrus production to achieve optimum nutrition. However, application rates of some micronutrients like Molybdenum (Mo) remain unknown. Therefore, a study is being conducted at UF/IFAS Citrus Research

Concerns about eutrophication that causes blooms of blue-green algae have strengthened over the last several decades due to the excessive use of pesticides and fertilizers, particularly those containing nitrogen (N) and phosphorus (P). These substances leached from agricultural fields and citrus groves into groundwater sources. Consequently, researchers developed best management practices (BMP) which are now being used to safeguard the environment while raising agricultural productivity. Additionally, Florida citrus production has decreased by more than 70% due to huanglongbing (HLB). Macro and micronutrient uptake is constrained owing to the decreased fibrous root density which may inflict root loss of up to 80%, depending on the severity of HLB-affected trees. The standard recommended rates of N and P were developed before the incidence of HLB and are no longer valid and warrant further refinement. Therefore, new site-specific guidelines are needed for the present situation. A study was started on 11-year-old ‘Valencia’ sweet orange trees (Citrus sinensis (L.) Osbeck) on Swingle citrumelo (Citrus paradisi Macf. × Poncirus trifoliata L. Raf.) rootstock in central Florida on Candler fine sand in 2023 to evaluate the impact of N and P fertilization on the growth and yield of HLB-affected citrus trees as well as to determine the optimal N and P rates for HLB-affected citrus trees in Florida. Eight treatments will be used over three years, with two N rates (112 and 224 kg/ha) as main plots and four P rates (0, 8.9, 17.8, and 35.7 kg/ha) as subplots in a factorial randomized complete block design. Tree height, canopy size, trunk diameter, fruit output, and juice quality are among the variables that will be measured. We anticipate that treatments that receive additional fertilization over the current recommendation have a significant chance of enhancing citrus growth and production. Keywords: Best management practices (BMP), Citrus sinensis, Huanglongbing, Site-specific nutrient management.

Florida stands as a significant player in the global citrus industry, boasting economic impacts of approximately 8.91 billion US dollars. Nevertheless, the citrus production in the state has been steadily decreasing since the onset of citrus greening (Huanglongbing, HLB) disease in 2005. Despite ongoing efforts, experts have yet to identify a potential cure for HLB, making the persistence of this disease a significant challenge for citrus production in Florida. In the wake of unavailability of a potential cure, different management strategies have been proposed aiming to minimize the HLB-induced adverse impacts on citrus plant growth and productivity and ensure the survival of citrus industry in Florida. In this context, effective nutrient management has emerged as a promising strategy for enhancing the performance of trees affected by HLB and sustaining a profitable yield. Fine root loss stands out as a primary concern in the management of HLB in citrus, as it impedes the plant's ability to uptake water and nutrients, resulting in nutritional imbalances. Effective nutrient management has the potential to effectively counterbalance the effects of fine root losses, thereby serving as a crucial factor in mitigating the adverse impacts of HLB on citrus trees. Therefore, this study has been initiated with the aim to evaluate the potential benefits of nutrient management on HLB affected mature Valencia sweet orange [Citrus sinensis (L.) Osbeck] trees. We seek to investigate the effects of different levels of nitrogen (N) i.e., 112, 168, 224, 280, 336 kg/ha on nutrient uptake, plant growth, fruit yield, juice quality, and overall performance of HLB-affected trees. In addition, nutrient mobilization in the soil in response to different levels of N has also been given critical consideration in order to evaluate the leaching potential of different nutrients and formulate mitigation strategies.

Florida citrus production and acreage have drastically decreased in the past years primarily due to citrus greening disease; consequently, citrus grove management has become more challenging and resource demanding. To increase soil health and restore tree and root health, new management practices have been implemented; in particular, a practice that has increased in use in the Indian River region is fabric mulch ground cover (FMGC). Potential advantages of FMGC include improved weed and pest control, reduced soil erosion, increased soil moisture and nutrient retention, reduced temperature extremes, and enhanced microbiome composition of the soil. Although the practice has been in use for almost ten years, little data has been scientifically collected from established groves. Hence, the goal of this trial is to evaluate the effects of FMGC on grapefruit tree growth and soil characteristics in the Indian River region. Four-year-old ‘Star Ruby’ (Citrus × paradisi) grapefruit trees grafted on ‘US-942’ (Citrus reticulata × Poncirus trifoliata) rootstock grown with or without FMGC were uniformly chosen for a two-year trial. A total of 20 trees were assigned to two treatments (FMGC vs. conventional). Leaf and soil nutrients, trunk diameter, height, canopy volume, and soil microbiome composition have been collected in the winter and summer. Gathered data showed initial differences in canopy volume, trunk diameter, and soil moisture between the two treatments. The trial will continue for an additional year, resulting in a greater understanding of the impact of this recently implemented management practice and its potential benefits to Florida citrus growers.

The Florida citrus industry has seen a 90% decline in fruit production, following the first identification of huanglongbing (HLB) in 2005. Sweet orange (Citrus sinensis) cultivars make up a majority of the juice industry and are known to be susceptible to HLB; therefore, new tolerant or resistant cultivars or crop protection treatments need to be explored. Of the sweet orange cultivars released by UF Institute of Food and Agricultural Sciences, ‘OLL’ lines have shown some potential tolerance to this disease in cultivar field trials. High-throughput phenotyping revealed that nearly 14% of top performing trees across roughly 90 different research blocks in Florida, were accessions derived from the original ‘OLL’ tree. Of these trees, ‘OLL-8’ represents 11% of top performing trees across these different research blocks. This research explores the effects of different rootstocks in combination with the ‘OLL-8’ scion. Three UF rootstocks (‘UFR-2’, ‘UFR-4’ and ‘UFR-6) and three industry standard rootstocks (‘US-897’, ‘US-942’ and ‘Swingle’) were compared. For each rootstock, 12 mature trees, across three different blocks were compared across three different time intervals during the 2023 and 2024 ‘Valencia’ harvest seasons at a field trial in Lake Alfred, Florida. In 2024, the same 12 mature trees per rootstock were compared with trees that received oxytetracycline injections following the previous harvest season. Data was collected on juice quality variables including total soluble solids, titratable acidity in citric acid equivalents, sugar:acid ratio, pounds solids per box, percent juice, and color as well as on external fruit quality data parameters such as mass, diameter, length, and color. Data were analyzed to determine statistically significant differences among the different rootstocks evaluated. To determine differences in tree health, high-throughput phenotyping via drone flight occurred in December of 2023 and March of 2024 and included variables such as tree count, measurements of canopy area and volume, normalized difference vegetation index (NDVI), and normalized difference red edge index (NDRE). There was evidence for statistically significant differences for various traits among the rootstock combinations evaluated in this study.

The citrus industry across the globe, including Florida, has been severely affected by the citrus greening disease (Huanglongbing, HLB), which is associated with the bacterium Candidatus Liberibacter asiaticus (CLas) and vectored by the Asian citrus psyllid. While no single method has been found to completely control CLas, ways to mitigate its effects on citrus trees have been increasingly studied. One recent management method that has been attracting attention is oxytetracycline (OTC) trunk injections. While initial research has shown that OTC trunk injections have been able to reduce HLB symptoms, there have been some inconsistencies about the extent of that reduction between different cultivars. A limited number of cultivars have been studied, mainly focusing on the sweet oranges ‘Valencia’ and ‘Hamlin’. The limited cultivars injected that are closely genetically related may cause differences in the effectiveness of treatment. There is a gap in knowledge about how OTC treatments affect cultivars with diverse genetic backgrounds. The aim of this study was to investigate the effects of OTC trunk injections on above and belowground tree health of various United States Department of Agriculture developed citrus cultivars. A completely randomized experimental design comprising 10-year-old mandarin, grapefruit, and sweet orange-like cultivars grafted on ‘US-942’ and ‘US-812’ rootstocks was used to study OTC trunk injection rates applied once a year at the recommended label concentrations (n = 21). Similarly, trees from the same cultivars grafted on the same rootstocks not receiving any injections were used as controls (n = 21). Throughout the experiment, above and belowground components were analyzed for any changes. Aboveground measurements included tree health within and between cultivars: canopy dimensions, leaf CLas titer, fruit size, drop and harvest count, and OTC residue in leaves. Belowground measurements included analysis of root and microbiome health by observing root density, root CLas titer, root OTC residue, and microbiome population diversity. The results are helping researchers to utilize OTC trunk injections more effectively.

In October 2020, the Republic of Korea set a landmark goal to achieve net zero emissions by 2050. However, the national greenhouse gas emission statistics did not account for carbon absorption by agricultural lands, including orchards, due to the absence of adequate calculation systems and data. Recognizing the significant role of photosynthesis in fruit trees like Citrus in carbon sequestration and climate change mitigation, this study aims to address this gap. We focused on developing allometric equations for estimating biomass and carbon stocks of citrus trees, particularly in orchards across Korea, with a case study on Jeju Island, a principal citrus cultivation area. Measurements of height, crown width, and the diameter of rootstock and trunks were conducted, observing an increase with tree age, though trunk diameter showed considerable variability. The study encompassed trees aged 5–45 years of the Satsuma Mandarin (Citrus unshiu Marc. cv. Miyagawa), a major citrus cultivar cultivated in Korea. Components including leaves, branches, trunks, and roots were harvested, dissected, fresh weighed, and oven-dried to develop dry to fresh weight ratios for dry biomass calculation. Allometric equations with trunk diameter as the sole independent variable were formulated for the Satsuma Mandarin tree. Furthermore, the total carbon content for trees aged 5–45 years was assessed through direct and destructive harvesting, revealing a carbon content range of 44.13 to 46.85% across different tree organs, with root carbon content increasing with age. This comprehensive study provides crucial insights into the biomass and potential carbon fixation capabilities of citrus trees, contributing significantly towards the accuracy of national carbon stock estimations. This work was carried out with the support of the Research Program for the National Institute of Horticultural

In this study, we investigated the variety-dependent survival of citrus seedlings and analyzed the pomological characteristics of fruits and thorn lengths following irradiation with gamma rays. Scions from the seedlings of the following citrus varieties, ‘Yuzu’, ‘Noeulhyang’, ‘Sarahyang’, ‘Namgam’ (nucellar), and ‘Meiwakumquat’ irradiated with gamma rays at 0, 60, 80, and 100 Gy were grafted onto trifoliate orange. At 6 months after grafting, the survival rates of ‘Yuzu’ and ‘Noeulhyang’ exposed to 100 Gy were 49.5% and 34.8%, and that of ‘Sarahyang’ and ‘Namgam’ (nucellar) exposed to 80 Gy were 51.6% and 46.8%, respectively. ‘Meiwakumquat’ exhibited the lowest survival among the varieties used in this study. Therefore, we classified ‘Meiwakumquat’ as highly susceptible to gamma radiation; ‘Noeulhyang’, ‘Sarahyang’, and ‘Namgam’ (nucellar) as intermediately susceptible; and ‘Yuzu’ as the least susceptible. We assessed the effects of gamma radiation on the pomological traits in irradiated ‘Tambit1ho’ and ‘Yuzu’. Among the 72 irradiated ‘Tambit1ho’ seedlings, the average seed number (number of seeds per fruit) varied between 0 and 18.6, whereas that in the unirradiated seedlings was between 8 and 18. Among the irradiated seedlings, the average seed number was less than 1.0 in eight seedlings. In addition, we observed variations in weight, rind and segment hardness, and sugar and acid contents. The thorn length of the flush in unirradiated ‘Yuzu’ was between 1.3 and 6.0 cm, whereas that of flush in gamma-irradiated seedlings was between 0.1 and 6.1 cm. Among the irradiated ‘Yuzu’ seedlings, the thorn length was less than 0.1 cm in two seedlings.(This work was carried out with the support of the Research Program for the National Institute of Horticultural

Citrus is one of the most valuable fruit crops globally and Florida historically has been known to be the major state producing sweet oranges for juice. Continuous efforts to develop new scion and rootstock varieties have been on-going in the University of Florida Citrus Breeding Program since the 1980s. Over the years numerous phenotypic data sets including big data from image-based phenotyping and large genotypic data sets from advances in sequencing technology have been generated. Efficient tools for data collection and management of both phenotypic and genotypic information are needed. To facilitate citrus breeding in Florida and elsewhere, the Citrus Genome Database (CGD, www.citrusgenomedb.org) has developed a Breeding Information Management System (BIMS) to store, manage, and analyze the phenotype and genotype data of private breeding programs. BIMS is compatible with Field Book, an Android App that allows for collection of phenotype data in a digital notebook on a tablet or phone. As a participant of the 2022-funded SCRI-project ‘Advanced National Database Resources for Specialty Crop Research and Improvement’, the UFL Citrus Breeding Program has adopted BIMS. This poster demonstrates the value of moving to electronic data collection using Field Book and the web-based management system BIMS. The goal of the UF breeding program for this project is to work together with citrus breeding programs across the U.S. and provide training on how to use BIMS and Field Book as well as adapt these tools to meet the needs of citrus breeders.