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
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
Comparing Scion and Rootstock Trunk Injection of Oxytetracycline for HLB Management Across Diverse Rootstocks in Florida - Larissa Nunes da Silva Evaluation of Different Oxytetracycline Rates Delivery by Trunk Injections on Mature Valencia Sweet Orange Trees - Gabriel de Castro Marconi Pugina Field Performance of Novel Citrus Rootstocks Grafted with Valencia and Their Response to Systemic Delivery of Oxytetracycline - Caroline de Favari Tardivo Florida-grown 'Hamlin' Sweet Orange Failed to Produce Adequate Pounds-solids Despite Budline, Environment, and Antibiotic Treatment - John Chater Hedging, Thinning, Controlled Release Fertilizer, and Oxytetracycline Trunk Injections to Mitigate Fruit Disorder Incidence in HLB-Affected 'Sugar Belle' Mandarin - Joe Volpe Grove First: A Framework to Find Citrus Greening Treatments that are Safe, Affordable, and Available.- Guilherme Locatelli Can We Improve Growth and Production in HLB- Affected Citrus Trees Using Plant Growth Regulators? - Prudhvi Vulchi Methyl Salicylate and Gibberellic Acid For The Rehabilitation Of HLB- Affected Sweet Oranges. - Gurleen Kaur
The huanglongbing (HLB) associated pathogen Candidatus Liberibacter asiaticus (CLas) inhabits the phloem of infected citrus trees, which impedes the efficacy of foliar-applied chemicals for management of the disease. Trunk injection is an alternate method that allows the targeted delivery of agrochemicals into the vasculature, resulting in their systematic distribution throughout the tree. This study aims to determine the large-scale efficacy of trunk injection of oxytetracycline (OTC) on citrus tree health, fruit quality, and yield in existing rootstock trials in a commercial production site in Florida. The study compares 9-year-old Valencia sweet orange (Citrus sinensis) trees grafted on six different rootstocks in a large field trial in Polk County, Florida. The experimental design is a complete randomized block design, with three injection treatments: 1) no injection (control), 2) injection into the scion trunk, and 3) injection into the rootstock trunk. The injections were performed in May 2023, and injected trees received a commercial formulation of OTC at a rate of 1.1 g per tree using FlexInject injectors. Data collection included HLB status, tree size, yield, fruit/juice quality, fibrous root density, and leaf macro- and micronutrient content once a year, wound phenotype every six months, and bacterial titers before injection and 3 days, 1 week, and 1 month after injection. OTC injections into the scion or the rootstock trunk improved tree health, yield, fruit/juice quality, and the leaf Ca content. Overall, injections increased fruit yield by 24% and juice brix by 9%, increasing the revenue by 36% on a per acre basis. Injection into the scion trunk was slightly superior in terms of tree growth and fibrous root density, while injection into the rootstock trunk reduced the wound size, bark cracking, and HLB symptoms. CLas titers were reduced regardless of the injection site one month after injections. In conclusion, our results suggest that OTC injections have the potential for short-term management of HLB to help with the recovery of the Florida citrus industry in the face of endemic disease conditions. The trial will continue to assess longer-term effects.
In Florida, Huanglongbing (HLB), also known as citrus greening, has severely impacted citrus production, prompting research into alternative treatment methods such as trunk injection of oxytetracycline (OTC) to manage Candidatus Liberibacter asiaticus (CLas) colonization. This study aims to 1) determine the optimal OTC rate administered by injection to improve the health and productivity of HLB-affected mature sweet orange trees and 2) determine the impact of spring versus late summer injections to maximize benefits and the potential for extending the harvest window. The study was initiated in 2023 in a commercial citrus production setting in Polk County, Florida. The trees were 18 years old and composed of ‘Valencia’ (Citrus sinensis) scion on Swingle (C. paradisi × Poncirus trifoliata) rootstock. Four different OTC rates (0.55 g, 0.852 g, 1.1 g, and 1.65 g active ingredient per tree) and two injection times (June and September) were compared against a control receiving no injections. The experimental design was a randomized block design with eight replications, and each replication consisted of four linear trees. A commercial formulation of OTC registered in Florida was used and administered through FlexInject injectors. A volume of 100 ml per tree was used for the 0.55-1.1 g rates and administered with one injector. The highest rate (1.65) was administered using two injectors on opposite sides of the tree in a volume of 75 ml per injector. Tree health was assessed by visual ratings of foliar HLB symptoms and canopy densities, while CLas titers were quantified using real-time PCR. Fruit quality and yield measurements included total soluble solids, titratable acidity, fruit weight, and juice characteristics. Trees were harvested, and fruit/juice quality was determined in March 2024. Overall, injected trees produced significantly more and larger fruit with better juice color, a higher percentage of juice, and more total soluble solids than control trees. The highest rate of OTC produced the highest yield and highest-quality fruits compared to the other rates. We did not observe any difference between spring (June) and summer (September) injections on any measured variables. Bacterial titers were reduced in the injected trees compared to the non-injected trees, and injected trees had fewer HLB symptoms and denser canopies than control trees. This research provides important insights into the best practices for managing HLB using trunk injection of OTC.
Worldwide citrus production faces significant challenges from the devastating disease Huanglongbing (HLB), necessitating innovative management strategies. This study aimed to assess the performance of novel rootstocks under natural HLB-endemic conditions using regular management practices and the recently registered practice of delivering oxytetracycline (OTC) through trunk injection to reduce pathogen load. Nine novel rootstocks, US-1673, US-1676, US-1680, US-1672, US-1687, US-1688, US-2111, US-2132, and US-2137 with different genetic backgrounds, including Citrus maxima, C. tachibana, C. reticulata, and Poncirus trifoliata were included in the study. Also included were two commercial rootstock standards, sour orange (C. aurantium) and Swingle (C. paradisi × P. trifoliata). The rootstocks were grafted with ‘Valencia’ sweet orange (C. sinensis) scion and planted in 2014 in a randomized complete block design and 12 single-tree replications in an open field in St. Lucie County, Florida. In July 2023, half of the trees were injected with ReMedium TI® (95.0% oxytetracycline hydrochloride) dissolved in reverse osmosis water acidified with muriatic acid to a pH of 2.0. Each tree received 0.75 g OTC dissolved in a volume of 75 ml (10,000 ppm) administered using FlexInject injectors. Injections were performed in the scion, approximately 5 cm above the graft union. Tree measurements included tree size, canopy health, pathogen titers, fruit yield, and juice quality. Significant differences among rootstocks were observed in the years before injection. In the 2022-2023 production season, US-1688 induced the highest yield, and US-2132 induced the best juice quality. Preliminary results indicate an overall positive response to the OTC treatment across all rootstocks. Injected trees had a 36% increase in yield, an 11% increase in juice brix, and a significant reduction in leaf and root pathogen titers. As in the previous years, growth and productivity varied significantly among the rootstock cultivars. US-1688, a new release by USDA under the name SuperSour 4, continued to be among the largest, healthiest, and most productive trees. The results from this research demonstrate the importance of rootstock selection for sustainable citrus cultivation. It also highlights the benefits of integrating the systemic delivery of antibacterial therapies to maximize the resilience of citrus trees to HLB.
Huanglongbing (HLB) is a devastating bacterial disease in Florida and has been spreading in citrus-growing regions in Texas, Georgia, and California. HLB threatens the entire US fresh and processed citrus industries. To date, all commercial sweet orange (Citrus sinensis L. Osbeck) cultivars are susceptible, though some are more tolerant than others. The citrus industry has an estimated economic impact nationwide of over $13 billion. The currently applied strategies for mitigating this disease are costly and unsustainable. The development and commercialization of HLB tolerant sweet orange scions is needed for sustainable and profitable citriculture in the US. Citrus Under Protected Screen (CUPS) is a method used in Florida to exclude the Asian Citrus Psyllid (Diaphorina citri Kuwayama, or ACP), which is a phloem-feeding hemipteran insect that is the vector for Candidatus Liberibacter asiaticus CLas the causal agent believed to be responsible for HLB disease in citrus. ‘Hamlin’ sweet orange is the most important early sweet orange for processing in modern history. ‘Hamlin’ has a budline called ‘Hamlin 1-4-1’, which is the predominant budline in the State of Florida. ‘Hamlin 1-4-1’ has high susceptibility to HLB, which causes symptoms such as blotchy mottle, small fruit size, high titratable acidity (TA), low total soluble solids (TSS), and severe fruit drop. ‘Hamlin N13-32’ is a new budline of ‘Hamlin’ sweet orange that appears to have enhanced tolerance to HLB in terms of tree health. ‘Hamlin 1-4-1’ and ‘Hamlin N13-32’ trees were followed for two years in multiple environments with and without treatments of oxytetracycline. Tree size, rootstock, fruit number, fruit size, TSS, TA, TSS:TA ratio, and pounds-solids data were collected to determine the effects of environment (CUPS versus outside grove), antibiotic treatment effects, and budline effects on production. There were some significant differences among groups for fruit quality, but more research is needed to determine effects of oxytetracycline, budline, rootstock and environment on ‘Hamlin’ sweet orange production.
Global citrus production has been severely impacted by huanglongbing (HLB), a disease presumably caused by the phloem-limited bacteria Candidatus Liberibacter asiaticus (CLas). While there are not any commercial citrus cultivars currently available that have total resistance to this pathogen, several varieties show some degree of tolerance, including the LB8-9 ‘Sugar Belle’ mandarin. This cultivar was released by the UF/IFAS CREC Plant Improvement Team in 2009 and is known to be one of the most HLB tolerant varieties in HLB-endemic conditions when considering tree health. Fruit from this cultivar can be used for juicing or in the fresh market and with proper cultural care the trees consistently produce relatively high yields with typically an acceptable ratio of total soluble solids (TSS) to titratable acidity and value in pounds-solids per acre. Despite the improved tolerance to HLB in ‘Sugar Belle,’ many growers in Central and South Florida have had increased incidences of fruit disorders with this variety in the past several seasons. Fruit that are misshapen, have a poor peel color, or go soft on the tree are more common making this cultivar often undesirable for packing houses. The objective of this study is to determine if hedging the trees at different times (early summer, middle summer, or late summer), manually removing ~50% of the developing fruit in July (thinning), controlled release fertilizer applications, or oxytetracycline trunk injections will help mitigate some of the incidences of fruit disorders and increase overall fruit and juice quality at harvest. There were two sites used for this experiment (The Citrus Research and Education Center in Lake Alfred, FL, and Tamiami Citrus “Bee Branch Grove” in Avon Park, FL) and it was conducted over two seasons 2022-2024. Significant differences (p-value < 0.05) were discovered among the treatment groups in terms of TSS, titratable acidity, sugar:-acid ratio, pounds-solids per box, fruit size, yield, percent asymptomatic fruit, and peel rupture force. Despite evidence that some treatments may provide benefits to the grower, more research is needed to mitigate the soft fruit problem in ‘Sugar Belle’ mandarin.
Citrus greening (Huanglongbing, HLB) is considered one of the most devastating diseases affecting the global citrus industry. There is an urgent need to provide relief from HLB and restore profitable citrus production. Since 2005, over a billion dollars has been spent on research to find a solution to HLB. Trunk injection with the antibiotic oxytetracycline is the current treatment that Florida growers are using to manage the disease. To broaden the number of molecules available to growers to treat HLB a framework was developed to efficiently screen molecules in citrus groves, selecting those that enhance tree health over a season. The framework is based on the principles of the design-of-experiments (DOE). Utilizing the injection system developed by TJ Biotech (LLC), 88 molecules were injected into 8-year-old ‘Valencia’ sweet orange (Citrus × sinensis) trees grafted on ‘US-812’ (Citrus reticulata × Poncirus trifoliata) rootstock over a six-week period. The injections were divided into nine sets, with varying numbers of molecules injected in each set (12, 10, or 6). The injections were administered into the scion, approximately 5 cm above the graft union. Visual assessments of tree health index and canopy density were collected to evaluate changes in restoring tree horticultural traits. Ratings were recorded before injections and at 90 and180 days post-injections. In addition to health index and canopy density, a series of seven pictures were taken per tree on the injection day and subsequently at 30, 60, 90, and 180 days after injections. Pre-harvest fruit drops were measured by counting and removing any fruits on the ground beneath each tree. The total number of fruits on each tree was tallied at harvest to calculate the percentage of fruit drops for each tree. Yield, fruit, and juice quality were assessed at harvest. In this screening trial, trees injected with oxytetracycline have been used as a positive control to indicate enhancement in tree health. Results from the tree health index obtained at 90 and 180 days after injection showed that 17 molecules performed similarly or better than the oxytetracycline-treated positive control. We are partnering with regulatory consultants to identify those that are safe and affordable. New molecules for injection will require regulatory labeling.
Emerging Pests and Pathogens Research Unit, USDA Agricultural Research Service/ Plant Pathology and Plant Microbe Interactions Section, School of Integrative Plant Science, Cornell University
Huanglongbing (HLB) disease is arguably the biggest concern for citrus growers in Florida causing a drastic more than 75% decline in citrus-bearing acreage since 2005. HLB symptoms include sparse canopy, poor leaf growth and development, ultimately resulting in yield losses. Standalone applications of plant growth regulators (PGRs) and certain antibiotics have been reported to reduce the impact of HLB on tree growth and promote new flush growth. However, very little research has been done on synergistic effect of PGRs and antibiotics on tree growth and yield. The goal of HLB mitigation strategies is to promote a denser canopy, enhancing source to sink ratio as trees with dense canopies are known to produce high fruit yield. Thus, we initiated a field study to evaluate foliar applications of PGRs (auxins, cytokinins, and gibberellins) and trunk injections of Oxytetracycline (OTC) in 9-year-old orchards of Valencia on ‘Swingle’ rootstock in central Florida. This is the first research in citrus where PGRs are being applied according to tree phenology. The experimental design is a split-plot with a completely randomized block design with 8 replications. The antibiotic programs (with and without OTC injections) are assigned to the main plots, while the PGR treatments assigned to the subplots consist of an no PGR control, PGR applications with varying concentrations, and PGR applications with constant concentrations throughout the year. Parameters such as leaf area, fresh weight, dry weight, water content, chlorophyll content, starch content and carbohydrate content from leaf samples are recorded every three months starting from July 2023. Over 9 months no consistent pattern of PGR or OTC treatment was observed for vegetative traits. Nonetheless, Non-OTC trees showed higher leaf water content compared to OTC during the dry season months of October and January. Regarding yield, the study suggests that both PGR treatments, when applied with or without OTC lead to significant improvement in yield. PGR variable treatment showed 30% improvement in yield efficiency compared to both the control and PGR Constant treatments. No difference is observed between OTC and Non-OTC programs in terms of yield efficiency. These findings suggest that use of PGR treatments regardless of use of antibiotics can be beneficial for growers.
Precision Nutrition Management: Finding Optimal Methods for Leaf Nutrient Analysis in HLB-affected Citrus Trees - Meryam Manzoor Cover Crop Effects on HLB-affected Citrus Tree Growth and Soil Characteristics: Results From a 3-year Field Trial - Lorenzo Rossi More Frequent Irrigation Increases Yield in HLB-Affected Sweet Orange - Tripti Vashisth Impact of Different Organic Matter Contents on ‘US-942’ Citrus Rootstock Physiology, Nutrient Uptake, and Root Morphology - Lukas Hallman Soil Amendment Strategies to Rehabilitate Freeze Damaged Citrus Trees for Sustainable Crop Management - Shad Nelson Physiological and Metabolomic Changes in Young Citrus Trees Under Elevated CO₂ and High Temperatures: A longitudinal study in Mandarins (C. reticulata.) - Taylor Hornburg Reports and research on incorporating cover crops in Florida citriculture, 1896 – 2024 - Lorenzo Rossi
Dr. Rossi’s research program focuses on improving root health and growth on cultivated crops, leading to the development of environmentally sound and effective management methods. He is a horticulturist with specific expertise related to plant stress physiology, root dynamics and... Read More →
Wednesday September 25, 2024 7:59am - 9:45am HST
South Pacific 1
Effective fertilizer management and accurate nutritional analysis are critical for healthy tree growth and maximum yield. Citrus trees perform best in the optimum range of each nutrient, and a deficiency or excess can result in poor tree growth and yield. Accurate fertilizer management decisions for citrus trees begin with proper leaf sampling. To accurately assess tree nutrition status, the appropriate time and procedure for collecting leaves for nutrient analysis must be followed. Historically, nutrient management for healthy citrus trees involved annual leaf sampling from July to August, with subsequent year fertilization plans based on single nutrient analysis. Currently, nearly all commercial Florida citrus orchards are affected by Huanglongbing (HLB), a systemic bacterial disease that affects all citrus varieties and rootstocks, causing extensive tree health decline. Studies suggest that a good nutrition program can improve the tree health and production of HLB-affected trees. However, the key is to supply the nutrients that are deficient or low. This widespread prevalence of HLB needs new approaches for managing fertilizer programs by regular leaf sampling to identify tree nutrient status and requirements. Thus, this study focuses to improve and revise the leaf nutrient sampling guideline for HLB-affected trees by determining the optimal time for leaf sampling and adjusting fertilization for increased production and tree health. Key objectives include assessing the frequency of leaf sampling required per year to capture the tree's nutritional status effectively and adjust fertilizer accordingly to establish the correlation of leaf nutrient concentration with the yield, fruit drop, and canopy density. For this study, spring and summer emerging flushes were tagged on HLB-affected ‘Hamlin’ and ‘Valencia’ mild and severe sweet orange trees in a central Florida orchard over two years. The leaves from tagged branches were collected every 3 months for leaf nutrient analysis and the results of both spring and summer leaves were used to adjust the fertilization plan accordingly. It was found that the spring emerging flush was optimal in adjusting the fertilizer for the highest yield compared to the summer emerging flush. With the use of precision fertilization, the improvement in tree canopy density and fruit yield was more obvious in mildly HLB-symptomatic trees compared to severely symptomatic trees. Our results demonstrate the growers should be performing nutrient sampling quarterly and use this information to precisely manage fertilization and improve tree productivity.
Citrus greening, or Huanglongbing (HLB), poses a severe threat to Florida’s citrus industry, impacting tree health and yield. Due to the lack of a known cure, growers employ various strategies to manage its effects, including increased nutrient application. However, in regions like the Indian River District (IRD), characterized by poor soil fertility and organic matter content, nutrient retention is challenging. Consequently, there is growing interest in using cover crops to enhance soil fertility. Despite this, there is limited published data on their effectiveness in the IRD. To address this gap, a collaborative study was initiated in Ft. Pierce, Florida, involving a commercial grower and the University of Florida. A three-year field trial, employing a randomized complete block design with four blocks, included ‘Star Ruby’ grapefruit trees grafted on ‘US-942’ rootstock, ‘Bearss’ lemon trees on ‘Sour Orange’ rootstock, and ‘OLL’ sweet orange trees on 'US-942' rootstock. Two treatments were applied: conventional (without cover crops) and experimental (with cover crops). Cover crops were planted bi-annually (winter and summer), grown, and terminated at each season’s end. Soil nutrient content, organic matter, microbiome diversity, moisture, and temperature, as well tree and root growth parameters were measured seasonally. After three years of cover cropping, significant differences in soil nutrient content, organic matter, and microbiome diversity were observed between the conventional and experimental treatments, suggesting potential impacts of cover crops on soil characteristics. However, there were no noticeable effects on tree growth or physiology. This study is ongoing and aims to provide a comprehensive understanding of the long-term effects of cover cropping on soil parameters in HLB-affected citrus groves, informing sustainable management practices in citrus cultivation.
Dr. Rossi’s research program focuses on improving root health and growth on cultivated crops, leading to the development of environmentally sound and effective management methods. He is a horticulturist with specific expertise related to plant stress physiology, root dynamics and... Read More →
Huanglongbing (HLB) causes a steady decline in tree health. Part of this decline includes root dieback which limits their capacity to take up water. For this reason, affected trees tend to be more susceptible to drought stress. This raises a significant concern during the dry season (Oct-May) when trees are largely dependent on supplemental irrigation for water. Unfortunately, most growers continue using irrigation schedules that were optimized for healthy trees. We hypothesized that irrigating more frequently, but in smaller doses would provide more opportunities for uptake and improve water relations in HLB-affected trees. The control treatment received the standard practice of irrigating every other day for 2 hours (12 gal/hr). The experimental treatment received water every day, 3 times a day, for 20 minutes (12 gal/hr). The two treatments received the same amount of water over the course of a week, but the experimental treatment received water more often. Treatments were initiated prior to flowering in January 2022 and were continued for two years. Tree water status improved in the experimental trees as reflected in higher mid-day leaf water potentials than in the control. This suggests the experimental regime was better able to maintain tree water status than the conventional method. In the second year, flowering was more synchronized in the experimental treatment. The control treatment saw two peaks in bud production with the latter one being consistent with a drought stress-induced flowering event. The experimental trees also saw an increase in fruit set in both years. Trees receiving the experimental and control treatments dropped a similar proportion of their crop load during June Drop and preharvest fruit drop in year 1 and 2. Finally, the experimental treatment resulted in significantly higher yields on average than the control in both year 1 and year 2 (72% and 200%, respectively). Altogether, more frequent irrigation improved tree productivity.
The disease citrus greening (HLB, Huanglongbing) continues to decimate Florida’s citrus industry, resulting in the lowest yields since the 1940s. With no cure or tolerant rootstock/scion combinations available, growers must manage the disease. Although increased fertilizer applications have been shown to improve tree health, the additional inputs are expensive and decrease operational profitability. As a result, interest has grown in improving soil fertility parameters such as organic matter, with the goal of reducing inputs and increasing horticultural sustainability. Despite the recognized potential of organic matter, little research has been undertaken to establish the optimal contents required to improve citrus root characteristics. The objective of this study was to answer two specific questions: what are the amounts of organic matter needed to significantly affect citrus root growth and physiology? And how does the incorporation of organic matter influence nutrient availability? To answer these questions, a six-month completely randomized greenhouse experiment was conducted to measure the impact of different soil organic matter contents on potted citrus trees. Six different treatments consisting of different organic matter contents (0% - control, 1%, 2%, 3%, 5%, and >10%) were created by mixing different amounts of locally sourced compost with sand. One-year-old ‘US-942’ (Citrus reticulata x Poncirus trifoliata) rootstock plants (n = 6 per treatment) were grown in the different mixtures for six months under controlled greenhouse conditions. During the study, soil moisture, plant height, and stem diameters were assessed every other month. At the conclusion of the study, total plant and root biomass, root nutrients, average root length, and average root diameter were measured. Results from the study indicated that higher organic matter contents (>2%) led to significantly increased plant biomass and stem diameter, and increased root growth. Significant results were also found at the soil level, where increased organic matter contents led to increased nutrient retention and increased root uptake of nutrients. Additional investigation is needed to better understand the advantages of increasing organic matter content, even by marginal percentages, utilizing grafted citrus trees of various cultivars in field trials. Such trials would provide insights into the practical implications of these findings within the industry.
Citrus in key citrus production states in the U.S. have been heavy hit from insect borne and disease pressures. The bacterial disease Huanglongbing (HLB) has had devastating impacts on the citrus industry in Florida. Despite having this threat to the Texas industry as well, the most recent negative impact to decrease citrus acreage has been due to harsh climatic events. In February 2021, citrus groves in south Texas were hit with icy weather that exposed orchards to prolonged freezing temperatures for several hours. The impacts of this one event reduced citrus orchards in south Texas by approximately 25% (over 2,800 ha or 7,000 acres). Climate variability has increased grower awareness to the potential for more frequent extensive drought and freezing winter periods. To better evaluate how to rehabilitate freeze damaged citrus trees, a two-year field study was created aimed at improving tree root health and soil conditions. Compost amendment (CA) was broadcast applied as well as application underneath the tree canopy of grapefruit trees in combination with varying nitrogen fertilizer rate application. Three fertilizer treatments: T1 (base rate = 112 kg N ha-1), T2=1.5x and T3=2x the T1 base rate were evaluated in a randomized complete block design with (11.2 Mg CA ha-1) and without CA in Rio Red grapefruits. Results indicated that root abundance significantly increased under composted trees compared to non-composted trees. Composted trees led to higher yields within 18 months following the freeze event compared to non-composted trees. The impacts of this research may aid Texas citrus growers and other producers looking to improve in-field management strategies that may assist in preparation for post-freeze weather events and extended seasons of water scarcity.
Dean and Professor, Texas A&M University Kingsville
Dr. Shad Nelson has serves as the Dean of the Dick & Mary Lewis Kleberg College of Agriculture & Natural Resource since 2016. Prior to this he served as a Professor teaching Horticulture Science courses and research in alternative irrigation strategies for South Texas Citrus industry... Read More →
As the atmospheric levels of CO₂ continue to rise, the concentration of carbon sources available for the plants also increases photosynthesis. The rise in atmospheric CO₂ is associated with global temperatures, resulting in an array of plant responses. Studies evaluating plant response to CO₂ treatments of 350 plant species show that plant responses are highly variable and species dependent, with the majority of studies being conducted on vegetable and grain crops, leaving a gap in understanding how tree crops respond. Mandarin (C. reticulata) trees are an economically important crop produced in California subject to climate change. This study used nursery trees of cv. Tango budded on C35 rootstock to determine the effect of elevated CO₂ exposure (400 ppm ambient vs. 800 ppm elevated) at elevated temperature (28°C ambient vs. 45°C elevated) to identify the physiological and metabolomic plant responses associated with each treatment. A longitudinal investigation was conducted over eight weeks in growth chambers (Conviron A1000, Winnipeg, CA) utilizing four treatment groups: ambCO2/Tamb (Control: CO2 400 ppm/Temperature 28°C); eCO2/Tamb (elevated CO2 at 800 ppm/Temperature 28°C); ambCO2/eTemp (CO2 at 400 ppm/Temperature 45°C); and eCO2/eTemp (CO2 at 800 ppm/ Temperature 45°C). Every two weeks, four replicates were collected from each treatment group. physiological measurements, photosynthesis response surveys, and metabolomic analysis were performed. Phenotypic measurements such as plant height, branches, leaf area, and leaf count showed that plant growth was impacted by treatment. Plant height, dry weight, and leaf count were significantly lower in the ambCO2/eTemp treatment as compared to the control (ambCO2/Tamb) as well as the other two treatments, indicating heat stress. Under elevated CO2 levels, trees were able to exhibit similar growth behaviors as the control treatment even under heat stress, signaling that the trees under eCO2 could compensate for a higher burden on carbon balance under heat stress. eCO2/Tamb trees accumulated significantly higher starch than all other treatments, whereas trees under both eTemp treatments showed significantly higher soluble sugars while significantly lower starch levels. This indicates that the trees under supplemental CO2 accumulate higher photoassimilates when they are free from heat stress, and the trees under heat stress exhibit starch conversion to soluble sugars as a stress response. Metabolomics analysis using Nuclear Magnetic Resonance (NMR) will provide valuable insight into the impact of treatment groups of eCO₂ and eTemp impact on Mandarin trees.
A forum for discussion of potential collaborations with regards to fruit, vegetable, and edible crops – i.e. citrus, breeding, production systems, postharvest, pomology, crop management, viticulture, etc.
A Glimpse of The Future of Citrus in Florida – The Millennium Block - Flavia Tabay Zambon Lessons from Evaluating New Varieties for the Indian River Grapefruit Industry - Flavia Tabay Zambon Florida Citrus Rootstock Selection 5th Edition: Artificial Intelligence Enhanced Mobile Application for Growers - Andres GonzalezNeira Australian Microcitrus-Derived Hybrids: Field Performance in Florida Under HLB Endemic Conditions - Matthew Mattia The Citrus Genome Database: A Resource for Citrus Research and Crop Improvement - Jodi Humann Comparative Transcriptomic and Metabolomic Studies Provide Insights into Early Tolerance Response of Citrus to CLas Infection - Zimmy Wang Exploring Leaf Nutrients and Fruit Quality Attributes Relationship in Fresh Market Citrus Using Artificial Neural Networks and Linear Regression Models - Shankar Shrestha
For the past two decades, Florida citrus production has undergone a 75% reduction due to Huanglongbing (HLB), a disease caused by Candidatus Liberibacter asiaticus and vectored by the Asian Citrus Psyllid (ACP, Diaphorina citri). To combat this threat, breeding programs have been developing new varieties, seeking those tolerant to HLB while possessing other desirable traits and providing a long-term solution for the citrus industry. The Indian River Research and Education Center is leading this effort by planting new scion and rootstock varieties in four independent trials at the Millennium Block in 2019. One trial consists of 18 grapefruit-pummelo hybrid scions grafted onto three rootstock varieties, totaling 54 combinations (Trial 1). The other three trials are rootstock trials, where ‘Ray Ruby’ grapefruit (Trial 2), ‘Glenn Navel’ sweet orange (Trial 3), and ‘UF-950’ mandarin (Trial 4) varieties are grafted onto 32 rootstocks. The Millennium Block is home to 5,500 trees. Complete data for the 2023/24 season was collected, evaluating fruit yield, weight, size, and juice quality across all trials except for the mandarins, which have yet to set and keep a harvestable crop. Fruits were categorized into “good fruit” (based on shape, size, and maturity) and “bad fruit” (including visually HLB-affected fruit and off-bloom fruit). One of the 18 scions in Trial 1, a grapefruit-orange hybrid with golden flesh and high juice content called ‘Triumph,’ was discovered through a fortuitous mistake, yielding over 19,000 lb/ac of “good fruit” when grafted onto X-639, and had a Brix of 8.18. ’Triumph’ exhibits visual tolerance to HLB, with minimal to no affected fruit and no leaf symptoms. Of the red flesh grapefruit, ‘UF-914’ grafted onto ‘US-942’ and ‘X-639’ yielded close to 12,000 lb/ac of “good fruit” each, with juice Brix between 8-9. The traditional ‘Ray Ruby’ grapefruit has produced more boxes per acre grafted onto UFR-15 (close to 8,000 lb/ac) than US-942 and Sour Orange. Meanwhile, ‘Glenn Navel’ sweet orange yields more boxes when grafted onto US-942 (approximately 3,800 lb/ac), UFR-17, and Kuharske. The rootstock trials reveal that grapefruit and sweet orange scions require distinct rootstock characteristics to achieve the best yields. Data gathered by these trials are essential for growers to make informed decisions about which varieties to plant compared to the available conventional scions.
Citrus greening is one of the deadliest bacterial diseases in citrus production. Caused by Candidatus Liberibacter asiaticus (CLas) and vectored by the Asian Citrus Psyllid (ACP, Diaphorina citri), the disease has devastated Florida’s citrus industry, reducing production by over 75% during the last twenty years. The Indian River Region, known for its premier grapefruit production, has suffered an intense decline in yield and acreage. Growers in the region have been fighting the pathogen and its insect vector, however, a long-term solution is required for sustainable grapefruit production. As no HLB resistance is known in commercially available cultivars, the University of Florida Breeding Program has bred new grapefruit hybrids with potential HLB tolerance. Plants developed through the program need to be field-tested. This study was initiated to evaluate new fresh grapefruit scion and rootstock breeding materials for HLB-tolerant. In collaboration with twelve growers across the state, a large trial was planted between 2020 and 2022 with 40 plots, each with forty-two scion/rootstock combinations totaling 12,000 trees. Among other tree growth data collected, fruit yield and quality were measured this season between October 2023 and March 2024. Results confirm that 'Jackson' grapefruit has some HLB tolerance, possibly due to its vigorous nature. However, its high fruit drop and inconsistent fruit set are persistent grower concerns. Among the newly developed grapefruit hybrids, 'UF N40-16-11-7' grafted onto SuperSour #1 and UFR-5, and the pummelo hybrid 'UF KW-50-1' grafted onto X-639 had low HLB disease indexes, equivalent to ‘Jackson’. On trees fruiting for the first time, the pummelo hybrid ‘UF KW-1-50’ grafted onto SuperSour #1 had the highest yield, mainly due to the pummelo heritage, followed by red grapefruit ‘UF N40-16-11-7’ also grafted onto SuperSour #1 and ‘Rio Red’ onto US-942. With tree ages ranging from 2 to 4 years, further data collection is needed to determine sustained yield and fruit quality. These results can help determine which combinations are most HLB-tolerant and best for planting in the Indian River Region.
Florida citrus production has declined by 81% in total tonnage since 2020, mainly due to the deadly citrus greening caused by Candidatus Liberibacter asiaticus (CLas), a fastidious, phloem-limited, unculturable, gram-negative, α-proteobacterium vectored by the Asian Citrus Psyllid (ACP). Over $1.5 billion in funds have been mobilized since 2006 to overcome this disease. As an innate immune response, the infected plant deposits callose and p-protein in the phloem sieve pore, decreasing the flow of photoassimilates, leading to a rapid decline and, eventually, a plant collapse. The high cost of production has economically devastated Florida citrus growers. Using HLB tolerant rootstocks is one alternative to mitigate CLas effects, and the growers depend on the University to provide the most up-to-date recommendations. To address this, we have developed a convenient mobile application that uses artificial intelligence (AI) to assist growers in making the best rootstock selection for their groves based on horticultural traits, abiotic tolerances, and specific disease/pest incidences. The Florida Citrus Rootstock Guide Expert System 5th Edition is planned to be released by 2025 and is based on the information released in the previous editions. In addition to the release of the mobile application on all major platforms, an interactive web-based rootstock table has been updated with recent field data and newly released rootstocks. Historical and unavailable rootstocks are excluded from the selection list, increasing the incidence rate for a well-suited rootstock selection. Users can download, send, and retrieve rootstock reports on their mobile devices. The app’s design was generated from grower/user surveys to be as user-friendly as possible. The expert system is built on the ES-Builder Web application, McGoo Software, and is developed utilizing Google’s Dart programming language. The University of Florida is committed to establishing an AI-based university. The app's scalability will allow it to fully integrate into future AI projects to combat epidemics like citrus greening.
At the Queensland Department of Agriculture and Fisheries, the breeding program used native Australian citrus species (C. australasica, C. australis, C. garrawayi, and C. inodora), collectively referred to as Microcitrus, and cultivated Citrus. Commencing in 1998, this program aimed to introduce desirable Microcitrus traits into cultivated citrus, resulting in hybrids with pedigrees ranging from 12.5% to 100% Microcitrus. Previous studies suggest that specific Microcitrus accessions may exhibit resistance to huanglongbing (HLB), a disease associated with Candidatus Liberibacter asiaticus (CLas). To assess this resistance, we conducted tests on these Microcitrus-derived seedlings in a Florida field site where HLB and its vector, the Asian Citrus Psyllid (Diaphorina citri; ACP), are prevalent. Seeds were received in August 2015 and grown into field-ready seedling trees at the USHRL greenhouse. In August 2018, these trees were planted in a randomized layout at the Fort Pierce USDA grove, comprising 53 Microcitrus-derived populations alongside grafted Clementine and Hamlin standards. During 2020 and 2021, a subset of these plants underwent 24 assessments for ACP colonization, focusing on periods of abundant citrus flush and active D. citri presence. Data collected included observations of eggs, nymphs, and 5th instars, indicating D. citri's ability to complete development on the plant. Statistical analysis assessed variations in egg and nymph abundances concerning scion and date, revealing differing nymph counts across dates and scion types, with Hamlin and Arrufatina X 09Q048 displaying the highest nymph counts. Additionally, all trees were evaluated for CLas levels in October 2021 and no significant differences were found. The study encompassed seedling development, field planting, and standard citrus production practices, with minimal pesticide usage to determine the tolerance of Australian-derived hybrids to HLB.
The Citrus Genome Database (CGD, www.citrusgenomedb.org) is a crop community database tailored for citrus researchers and breeders. CGD includes the Breeding Information Management System (BIMS) for both private breeding program management and publicly available phenotype and genotype data. Genetic data include genetic markers, maps, QTL, and GWAS curated from published and integrated with associated data in the database. The data is accessible via several search interfaces. Genetic maps can be viewed through the MapViewer tool, that also visualizes gene and genome data where available. CGD has over 40 genomes of Citrus and other genera in the Rutaceae family. For plant genomes, additional functional annotation and synteny analyses are conducted and made available to search. The genomes can be viewed in JBrowse, sequences searched using BLAST, genome synteny viewed with Synteny Viewer, and metabolic pathways for representative genomes can be viewed and users can overlay -omics data in CitrusCyc. Expression data associated with genes or mRNA of genomes in CGD are also available to view in the Expression Heatmap tool and on the feature page for the corresponding gene/mRNA. Ten bacterial genomes from Ca. Liberibacter and Liberibacter species are also available to search in the database, view in JBrowse, and search the sequences using BLAST. Researchers can also prepare and submit published data to the database using Excel based templates.
Citrus Huanglongbing (HLB, or citrus greening disease) has caused over 90% production losses since it was first reported in Florida in 2005. The unknown pathogenicity of the causative pathogen CLas hinders the development of sustainable disease management. Thus, understanding citrus host response to CLas, particularly at initial infection stage, is important for early disease detection and effective long-term HLB management. In this study, transcriptomic and metabolomic studies were conducted in a 2-day-post-inoculation (dpi) window, between HLB-tolerant LB8-9 Sugar Belle ® mandarin-like hybrid (SB; Citrus reticulata) and HLB- sensitive Valencia sweet orange (VAL; C. sinensis). CLas inoculation treatments included two controls no asian citrus psyllid (ACP) and CLas-negative ACP, plus CLas-positive ACP. Data were collevted at four time points: 2-, 12-, 24-, and 48-hour-post-inoculation (hpi). The results reveal that SB indicates immediate transcriptomic-level response from 2 hpi, compared with the delayed response in VAL from 24 hpi. The initial CLas-responsive differentially expressed genes (DEGs) in SB are related to plant defense response to Gram-negative bacterium, kinase activity and protein-kinase derived complex. DEGs that are categorized in plant defense response to Gram-negative bacterium are mostly associated with the pectinesterase inhibitors (PEIs) family which primarily alters the localized pH of the cell wall and strengthens cell wall integrity. On metabolomic level, SB shows rapid and high flavonoid content accumulation that reduces CLas-triggered stress and counteracts the initial infection. In VAL, the low flavonoid content accumulation removes reactive oxygen species (ROS) less efficiently which leads to more stress and cell death. Further investigation and validation on the proposed pathway are needed to confirm the early stage transcriptomic and metabolomic response of citrus tolerance response to CLas infection.
The market value of fresh citrus fruit is greatly influenced by the internal and external fruit qualities, such as peel color, total soluble solids (TSS), titratable acid (TA), and fruit size. Abundance or deficiency of mineral nutrients in citrus trees are among the most important key factors that affect fruit qualities. Various regression models using leaf nutrient parameters and quality indices have been suggested, but their accuracy and generalization performance in estimating fruit quality remain insufficient. In this research, we used both artificial neural network models (ANN) and a multiple linear regression model to explore the effects of leaf nutrient concentration on citrus fruit quality. For ANN models, we applied two transfer functions and five different training functions to establish the model with best prediction accuracy using TensorFlow framework through Python software. The models were evaluated using statistical performance evaluation criteria including the coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE), and mean absolute relative error (MARE). Sensitivity analysis of the prediction models was conducted to discern the significant contribution of leaf mineral nutrients to the respective fruit quality parameters. The response surface analysis determined the optimal range of these mineral elements, which is critical for guiding precision fertilization in fresh market citrus fruit for improving fruit quality. Comprehensive results will be presented during the conference. Keywords: artificial neural network, fruit quality, citrus, mineral nutrients, sensitivity analysis
The USDA National Plant Germplasm System (NGPS) is an invaluable resource to researchers and breeders of horticultural crops. Crop Germplasm Committees, with members from academic, private and governmental organizations provide expertise in a variety of topics, including collection priorities and vulnerabilities, identifying important traits for evaluation, and reviewing Plant Exploration and Evaluation grant proposals. The CGCs are a great opportunity for ASHS members to get more involved in setting germplasm related priorities for their crops of interest. This session gives an overview of the activities of the CGC and highlight activities of 3 specific CGCs. The talks will be followed by a 30-minute discussion session on avenues for increased interaction between the ASHS PIGs and the CGCs to ensure that germplasm collection priorities are relevant to the needs of stakeholders.
Coordinator(s)
Cecilia McGregor, University of Georgia, Athens, GA, United States
Speaker/Participant(s)
Gayle Volk, USDA, Fort Collins, Colorado, United States Introduction to Crop Germplasm Committees: An Opportunity to have an Impact on Crop Collections in the USDA-ARS National Plant Germplasm System (20 mins) Summary: The USDA-ARS National Plant Germplasm System (NPGS) maintains over 620, 000 accessions of more than 200 crops at 22 sites around the United States. Most crop collections have Crop Germplasm Committees (CGC) that provide guidance to the curator with regard to vulnerabilities, acquisitions, maintenance, genotypic characterization, phenotypic evaluations and distribution. CGCs welcome new members to improve the quality and impact of the NPGS collections.
Glenn Wright, University of Arizona - Yuma Agriculture Center, Yuma, AZ, United States The Rewards and Challenges of Chairing Two Crop Germplasm Committees (20 mins) Summary: The Citrus CGC and the Date Palm CGC are both affiliated with the National Clonal Germplasm Repository for Citrus and Dates in Riverside, CA. Membership of both committees include representatives of the federal government, academia, and industry. Activities of both committees include advising the NCGRCD on critical issues, including staffing, infrastructure, threats to the genebank, and germplasm backup, acquisition, sanitation, and distribution. We also advise repository staff on project plans, relevant research, and strategic planning. Finally, the committees comment and approve germplasm evaluation, plant exploration and plant exchange proposals.
Kim Shearer, The Morton Arboretum, Lisle, IL, United States Seeing the Forest for the Trees (20 mins) Summary: The Woody Landscape Plant Crop Germplasm Committee has a somewhat unique task in that the wild crop relatives can include all of the trees and shrubs of all of the forests. As a group, we found that the task of identifying priorities and vulnerabilities limited to specific taxonomic categories seemed insurmountable. How could we predict an event like the introduction of emerald ash borer (Agrilus planipennis) wiping out native floodplain forests and masses of street trees? What can be lost in an uncertain future with the onset of climate change? And how could we communicate this vulnerability in a way that was politically palatable? In this talk, the strategy for developing a new crop vulnerability statement and QUAD will be presented along with some examples of projects that have been funded and implemented for both plant exploration and evaluation.
Cecilia McGregor, University of Georgia, Athens, GA, United States Crop Germplasm Committees: An Opportunity for Value-added Research (20 mins) Summary: The Cucurbit Crop Germplasm Committee (Cucurbit CGC) includes experts from local and global academic institutions and private industries, as well as the federal government. In addition to the routine activities of the CGC, the participation of several Cucurbit CGC members in the federally supported SCRI CucCAP and CucCAP2 projects provided the opportunity for improved coordination and alignment of federally funded academic research and germplasm priorities This contributed to the development of tools and resources that adds value to the existing Cucurbit germplasm collections.
Encouraging Homeowner Citrus in Florida - David Austin Effect of Molybdenum Fertilization on Young Huanglongbing-Affected Citrus Trees - Kondwani Kamsikiri Investigating the Impact of Macronutrient Management on Performance of Huanglongbing (HLB)-Affected Sweet Oranges- Monkia Peddapuli Modifications in Existing Nitrogen Recommendations for HLB-Affected Sweet Orange Trees in Florida - Noor Ul Basar Evaluating the Impact of Fabric Mulch Ground Cover on Grapefruit Tree Growth and Soil Characteristics in the Indian River Region of Florida - Audrey Beany High-throughput Phenotyping and Fruit Juice Quality of 'OLL-8' Sweet Orange Scion on Different Rootstocks with Comparison of Oxytetracycline Injections - Emily Worbington Assessing Tree and Root Responses of Various HLB-affected Citrus Cultivars Using Oxytetracycline Trunk Injections - Giancarlo Buzzi Insights from a Citrus Breeding Program: Leveraging the Citrus Genome Database and Breeding Information Management System - Ronald Tapia
David Austin is a Residential Horticulture Agent for UF/IFAS Extension, Highlands County, and their Master Gardener Volunteer Coordinator. He has a Bachelor of Science in Horticulture from the University of Florida in 1984 and is presently working on his Masters in Landscape Pest... Read More →
Friday September 27, 2024 12:14pm - 1:35pm HST
Kahili
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.
David Austin is a Residential Horticulture Agent for UF/IFAS Extension, Highlands County, and their Master Gardener Volunteer Coordinator. He has a Bachelor of Science in Horticulture from the University of Florida in 1984 and is presently working on his Masters in Landscape Pest... Read More →
Friday September 27, 2024 12:15pm - 12:25pm HST
Kahili
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 & Education Center to evaluate the effect of varying rates of Mo on citrus tree growth and biomass accumulation of 2-year-old HLB-affected and HLB-free Valencia (Citrus sinensis L. Obserk) on Swingle citrumelo rootstock under greenhouse conditions. Four varying rates of Mo (0.0 kg·ha−1 Mo (Control), 1.12 kg·ha−1 Mo (1×-standard rate), 2.24 kg·ha−1 Mo (2×-standard rate), and 4.48 kg·ha−1 Mo (4×-standard rate) are applied to both HLB and non-HLB trees in a completely randomized design. Preliminary results from the study show that different Mo rates impact tree growth. In HLB-affected trees, 4.48 kg·ha-1 (4×-standard rate) Mo treatment resulted in the lowest height, probably due to toxicity, while 2.24 kg·ha-1 (2×-standard rate) treatment had the lowest height among unaffected trees. No significant differences in trunk diameter were observed among HLB-affected trees, whereas those subjected to 4.48 kg·ha-1 (4×-standard rate) showed the smallest trunk diameter among unaffected trees. The results also showed no statistical differences between above-ground and below-ground biomass accumulation and leaf Mo uptake. Our findings suggest that applying 4.48 kg·ha-1 (4× UF/IFAS current standard rate) may adversely impact key plant growth parameters.
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.
Alisheikh Atta currently works at the Department of Soil, Water, and Ecosystem Science, University of Florida. Alisheikh does research on HLB-affected citrus nutrient and water management. He studies the impact of plant nutrients on the performance of citrus trees, irrigation water... Read More →
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.
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.
