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.
