ASHS 2024 Conference

Multiple Foliar Applications of Ethephon for Growth Control of Lantana Camara - Lark Wuetcher
Ethephon Substrate Drenches Control Growth of Containerized Annual Bedding Plants and Herbaceous Perennials - William Rich
Microbial Communities in the Vertical Profile of a Container Substrate - Silvia Valles Ramirez
Moisture Content Effects Microbial Activity in Substrates Derived from Five Different Hammermilled Wood Species Over the Course of Greenhouse Petunia Production - Amanda Mizell
Stratification significantly reduces the phytotoxic effects of fresh hardwood - Andre Truter
The Use of Machine Learning to Develop Refined Foliar Tissue Analysis Standards and Diagnostic Tools for for Petunia - Patrick Veazie
Increasing the Nighttime Lighting Duration Can Hasten Flowering of Long-day Plants -Qingwu Meng
Extended Storage of Cut Flowers Using Sub-zero Temperature - John Dole

Lantana (Lantana camara) is a popular annual bedding plant among consumers because it is heat tolerant and attracts pollinators with its vibrant and often multi-colored flowers. Greenhouse growers commonly apply plant growth regulators (PGRs) to control lantana growth and produce a compact, well-branched, and flower. Introduction of new lantana cultivars instigates review of previously known PGR recommendations. As such, the objective of this study was to evaluate the effectiveness of multiple foliar spray applications of ethephon [(2-chloroethyl) phosphonic acid] to control growth and stimulate branching of lantana ‘Bandana Red’. Unrooted cuttings of lantana were received from a commercial propagator and stuck into 105-cell plug trays (30-mL individual cell) filled with a propagation mix. Cuttings were propagated for 35 d under 23 °C air temperature, 24 °C root-zone heating, and a daily light integral of 12 mol·m–2·s–1. Rooted liners were transplanted into individual containers (11.4-cm; 600 mL) filled with a commercial peat-based substrate. Beginning 7 d after transplant, eight single-plant replicants received 1 to 3 foliar spray applications on a weekly basis containing 0 (control; deionized water), 250, 500 or 750 mg·L–1 ethephon. Plants were grown in a glass-glazed greenhouse at 20 °C under ambient daylight supplemented with a photosynthetic photon flux density of ≈125 µmol·m–2·s–1 delivered from LED arrays from 0600 to 2200 HR (16-h photoperiod) to achieve a daily light integral of 12 mol·m–2·d–1. At 42 d after transplant, plants were destructively harvested, and data collected. In general, multiple foliar spray applications with increasing ethephon concentrations affected lantana plant height, diameter, branch number, and shoot dry weight to different magnitudes. For example, lantana plant height was suppressed by 21% to 39% (12.7 to 9.7 cm) from 250 to 750 mg·L–1 ethephon, respectively, compared to untreated plants and were more compact as applications increased. Plant diameter decreased by 13% to 19% (25.5 to 23.7cm) compared to untreated plants as concentration increased from 250 to 750 mg·L–1, respectively, and as spray applications increased. A similar trend was observed for branch number and shoot dry weight. Overall, multiple foliar spray applications of 250 to 750 mg·L–1 ethephon can control the growth of lantana ‘Bandana Red’; however, growers will need to conduct in-house trials to evaluate the level of control desired. Further studies investigating the effects of multiple foliar spray applications with increasing concentrations of ethephon on additional lantana cultivars are warranted.

Containerized annual bedding plants and herbaceous perennials account for 57% of the 2020 U.S. floriculture market with a reported combined wholesale value of $3.2 billion. To produce high-quality, compact containerized ornamental plants, foliar spray applications and substrate drenches of plant growth regulators (PGRs) are often utilized. Ethephon [(2-chloroethyl) phosphonic acid] is a common PGR used to control growth, stimulate branching, and manipulate flowering, but is only labelled for foliar applications. Therefore, our objective was to evaluate the response of 35 floriculture species drenched with increasing concentrations of ethephon. Annual bedding plants and herbaceous perennials were received as unrooted cuttings and propagated at 23°C under 10 mol·m–2·s–1 for 21 or 28 d, respectively. Plants were transplanted into containers filled with a soilless substrate and grown in a glass-glazed greenhouse at 20°C under 14 mol·m–2·d–1. At 10 d after transplant, eight single-plant replicates received a substrate drench of 296-mL aliquots of solution containing 0 (control; deionized water), 25, 50, 75, 100, or 200 mg·L–1 ethephon for annuals or 0, 125, 250, 500, 750, or 1,000 mg·L–1 ethephon for herbaceous perennials. Plant growth metrics including height, diameter, shoot and root dry weight were determined 6 weeks after transplant. Time to flower was determined for select species by recording the date of anthesis for each plant. In general, plant height of annual bedding plants and herbaceous perennials were suppressed and shoot and root dry weight reduced as concentrations of ethephon increased. For example, petunia (Petunia × hybrida ‘Flame Red’) drenched with 200 mg·L–1 was ≈40% (5.8 cm) shorter than untreated plants. Similarly, in dahlia (Dahlia × hybrida ‘Dark Red’) height and diameter were decreased by 50% (15.4 cm) and 30% (12.4 cm), respectively as concentrations increased from 0 to 200 mg·L–1. In digiplexis (Digiplexis × hybrida), substrate drenches increasing from 0 to 1,000 mg·L–1 ethephon reduced shoot dry mass by ≈55% (17.1 g). Root dry weight of catmint (Nepeta faassenii) was reduced by 35% (1.54 g) as concentrations increased from 0 to 1,000 mg·L–1. Time to flower was unaffected at all concentrations of the species selected. These growth and development trends were reflected in most of the species evaluated. As such, this research demonstrates that ethephon, if labelled for substrate drenches, provides adequate growth control of floriculture crops.

A moisture gradient exists in containers filled with soilless substrates where the substrate is wetter at the bottom of the container and becomes drier towards the top of the container. This moisture gradient affects other substrate chemical properties and therefore may affect biological properties including the microbial communities present. Microbial communities in soilless substrates have only recently been studied and little is known about their uniformity throughout the container. This research aimed to evaluate how the bacterial and fungal portions of the microbial community may change along the vertical profile of a container substrate. A substrate was mixed that consisted of manure compost, peat moss, and perlite (20:65:15 v/v) and planted with a single sunflower seedling. After 0, 3, and 6 weeks in a greenhouse environment, samples of soilless substrate from the top, middle, and bottom of the container (approx. 4.3 cm depth for each layer) were collected for DNA extraction. Bacterial and fungal communities were characterized by sequencing PCR amplified 16s rRNA genes and ITS regions, respectively. We found that the phyla Pseudomonadota, Bacteriodota, and Ascomycota were present throughout the container profile in all three layers. However, bacterial genera Paucibacter, Pseudomonas, and Iodophanus, and fungal genera Cercophora and Mortierella differed in abundance within each layer. Pseudomonas tolerant to negative abiotic factors were greater in the bottom layer after 6 weeks. Likewise, Coprinellus , responsible for lignin and cellulose degradation, was also present only in the bottom layer. The diversity of bacterial communities differed between layers, with the greatest in the middle and the lowest in the top layer. The percentages of all bacterial amplicon sequence variants (ASVs) that were shared among the three layers at 3 and 6 weeks were only 16% and 28%, respectively. The diversity of fungal communities was less affected by layer and time, but the percentages of shared fungal ASVs among layers were still only 27% and 28% at 3 and 6 weeks, respectively. In consequence, it is necessary to consider sampling technique and location when collecting a DNA sample from a container substrate.

Recently, the limited availability of Sphagnum peat moss due to poor weather conditions impacting harvests, and additional scrutiny from media and public outlooks has brought up serious questions about the long-term security of peat use in the horticulture industry. The search for alternative amendments began decades ago, with several products being evaluated over the years. Many have been found suitable for niche production settings, with few seeming to fit the industry somewhat ubiquitously. Of these, wood fiber is seemingly the most promising as it is a renewable resource that is available globally. Wood fiber amendments have been trialed extensively with industry emerging and scaling internationally. Wood can be processed to support many different applications in horticulture, giving it more robust qualities than other top components. There are some disadvantages to wood usage, namely, nitrogen immobilization. Wood contains large amounts of easily degradable carbon. Therefore, microorganisms will consume this carbon for energy by utilizing plant available nitrogen causing plant nutrient deficiencies. Microbial community activity is heavily influenced by moisture. Considering this, a study was developed to observe how the microbial activity of different hammermilled wood tree species may be influenced by moisture content in a greenhouse crop production cycle. Five tree species (Abies concolor, Calocedrus decurrens, Pinus lambertiana, Pinus ponderosa, and Pseudotsuga menziesii) were harvested in California and hammermilled. The wood particles were blended with a commercial peat-based substrate at 30% (by vol.). Supertunia ‘Honey’ plugs were planted in each of the substrate blends and grown on a greenhouse bench for 75 days. The crops were held at 25% and 35% volumetric water content using cantilever-style lysimeters and fertigated with water-soluble fertilizer, weekly. Crop growth and performance was assessed throughout production. Substrate CO2 was assessed pre- and post- production to assess microbial activity. The results will help assess the potential of utilizing differing tree species for wood fiber, and understand any adjustments that will be necessary to production practices.

With a global increased demand for growing substrates and specifically wood alternative substrates, methods are being tested to better understand wood as a product and how to incorporate wood into growing medium substrates. This study investigated the use of fresh whole-tree loblolly pine and whole-tree hardwood in horticultural greenhouse settings, focusing on how varying wood blend compositions and levels of stratification affect plant growth. Analysis revealed that increasing hardwood percentage in blends led to decreased plant growth, while stratification reduced differences among blends. Notably, at lower stratification levels, plant growth resembled that of the control treatment. Statistical tests confirmed these trends, highlighting the significant impact of wood blend composition on plant dry weight. Findings suggest that while hardwood incorporation decreases growth, stratification can mitigate differences among blends, allowing for the incorporation of untreated wood material. These results offer insights for optimizing wood blend usage in greenhouse cultivation, providing sustainable solutions for horticultural practices. Key Words: Hardwood, Stratification, Phytotoxicity, Wood Blends, Plant Growth.

Foliar tissue analysis is utilized to diagnose a crop's nutrient status. For most floriculture crops a survey approach of a small population of plants (n= <25) of healthy appearing plants are used to establish sufficient nutrient standards. While this historical approach offers a baseline for the wide variety of floriculture crops there is a need for scientifically based ranges similar to those available in agronomic crops. For fast-maturing crops, utilizing foliar tissue analysis and correctly interpreting the results is critical in making fertility adjustments when problems arise. Foliar tissue analysis results of petunia (Petunia hybrida) were compiled from a variety of diagnostic and research institutions to account for variations of growing environments and classified into five ranges (deficient, low, sufficient, high, and excessive). To aid in foliar tissue analysis interpretation machine learning models were evaluated for accurate percent correct classification (PCC) into the sample's respective nutrient classification. Four separate machine learning algorithms were performed to analyze the data set including sequential minimal optimization (SMO) of support vector machines (SVMs) and multilayer perceptron (MLP) artificial neural network (ANN), and two decision tree models J48 and Random Forest (RF). Machine learning algorithms were compared to identify significant model nutrients based on a complete foliar tissue analysis report of 11 elements for the observations. The performance of both machine learning algorithms SMO and MLP were determined using PCC and during the cross-validation. By evaluating the foliar tissue concentration dataset of multiple species by 10-fold and 66% split cross-validations, the incorporation of five elements of ranked based on Shannon Entropy (Information Gain) was able to correctly classify tissue concentrations into one of five foliar nutrient classifications greater than traditional statistics. This information provides additional insight as to how examining nutrient relationships can assist in identifying fertility problems and classifying nutrient ranges.

Low-intensity (≈ 2 μmol·m−2·s−1) photoperiodic lighting is often delivered at night to promote flowering of long-day greenhouse ornamentals when natural days are short. Adding sufficient far-red (FR) light to red (R) light is necessary for the most rapid flowering in some crops, including snapdragon (Antirrhinum majus) and petunia (Petunia × hybrida). Specialty light-emitting diodes (LEDs) that include R FR light are effective at floral promotion but cost-prohibitive, whereas common warm-white (WW) LEDs lack sufficient FR light and can delay flowering. Because the duration to saturate flowering is longer than currently used (e.g., 4–8 hours) for some long-day plants, we conducted a replicated greenhouse experiment to determine how the WW or R FR LED lighting duration influenced flowering. We grew snapdragon ‘Liberty Classic Yellow’, petunia ‘Easy Wave Burgundy Star’, and petunia ‘Wave Purple Improved’ under truncated 8-hour natural short days with or without WW or R FR (1:1) LEDs operating for 0, 4, 8, 12, or 16 hours in the middle of each night throughout the experiment. Snapdragon flowered 13–16 days earlier under R FR LEDs than under WW LEDs regardless of the lighting duration. Increasing the lighting duration from 0 to 16 hours decreased flowering time by up to 16 days and decreased plant height and leaf number at flowering under R FR LEDs, but not under WW LEDs. For petunia ‘Easy Wave Burgundy Star’, although WW LEDs delayed flowering by 6–13 days but promoted lateral branching compared to R FR LEDs, the gap in flowering time narrowed as the lighting duration increased from 4 to 16 hours. Increasing the lighting duration improved the efficacy of WW LEDs, but not R FR LEDs. Flowering of petunia ‘Wave Purple Improved’ was unaffected as the lighting duration increased from 4 to 16 hours regardless of the lamp type and was delayed by 6–10 days under WW LEDs than under R FR LEDs. For both petunia cultivars, flowering time was similar under 16-hour WW LEDs and 4-hour R FR LEDs. In conclusion, increasing the nighttime lighting duration increased the efficacy of WW LEDs at promoting flowering of petunia and increased the efficacy of R FR LED lamps at promoting flowering of snapdragon. Delivering WW LEDs all night long can minimize flowering delay in petunia compared to R FR LEDs. In contrast, sufficient FR light was indispensable to promote flowering of snapdragon, for which WW LEDs were ineffective.

The cut flower industry needs postharvest techniques that allow for extended storage of fresh cut flowers to meet consumer demands. We evaluated the use of sub-zero storage temperature (-0.6 °C) to maintain viable flowers with improved or comparable vase life to flowers stored at the industry standard (4 °C) without sacrificing aesthetic appeal. The vase life of 17 commercially important cut flower species: alstroemeria, anemone, campanula, carnation, chrysanthemum, delphinium, freesia, gerbera, gypsophila, larkspur, lily, lisianthus, ranunculus, rose, stock, sunflower, and tuberose, when stored dry at -0.6 °C for durations of 4, 8, and 12 weeks was comparable to or longer than when stored at 4 °C. Tuberose stems were not viable after holding for any storage duration or temperature. Stems of carnation benefited from an 8-hour pre-storage pulse with a hydrating solution and maintained a similar vase life to non-stored control stems when stored for 4 weeks at -0.6 °C. Conversely, rose stems only maintained similar vase life to non-stored control stems when held at 4 °C for all pre-storage pulsing solutions (water, hydration or holding solution). Vase life of lily and chrysanthemum declined for all pre-storage pulsing solutions and stems only remained viable after 8 weeks storage when held at -0.6 °C. Additionally, stored chrysanthemum and lily stems had a longer vase life when stored at -0.6 °C than when held at 4 °C after 4- and 8-weeks storage, respectively, for all pre-storage pulsing solutions. Experiment 3 further evaluated carnation, lily, and rose stems with and without a pre-storage acclimation period at 4 °C for either 24 hours or 1 week prior to extended storage durations of 4, 6, or 8 weeks. Holding stems at 4 °C for 1 week prior to extended storage reduced vase life of all species. Rose stems remained viable after 8 weeks of extended storage when held at -0.6 °C, but only when no pre-storage hold was used. Lily and rose stems were not viable beyond 4-week storage durations when held at 4 °C, but remained viable with no pre-storage holding period after 8 weeks at -0.6 °C. Carnation stems maintained longer vase life irrespective of a pre-storage holding period when stored at -0.6 °C. Through this work we show that that many species of cut flower may be held at sub-zero temperature with improved or comparable vase life to the industry standard of 4 °C.

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

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 & 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.

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.

Introduction of modern tools to the University of Arkansas System Division of Agriculture Fruit Breeding Program - Carmen A. Johns
A Century of Pear Breeding at the USDA - Christopher Gottschalk
Differential Thermal Analysis of Cold Hardiness in Interspecific Hybrid Grapevine for Breeding Applications - Douglas Vines
Ovary and Fruit Shape Variation Associated with Novel ClSUN25-26-27a Alleles in Watermelon - Samuel Josiah
Linking Cultivar Evaluations – Phenology, Metabolomics, Consumer Preferences, and Postharvest Handling of ‘Glenn’ Mango - Jonathan H Crane
Evaluation of Small Fruit Germplasm at the North Willamette Research and Extension Center - Patrick Jones
Developing a Genomic Framework for Selection of Fruit Attributes in Cold Climate Interspecific Grapes (Vitis Spp.) - Venkateswara Rao Kadium
U.S. Peach Production and Breeding Overview - Chunxian Chen

The University of Arkansas System Division of Agriculture (UADA) has a legacy breeding program that has spanned three fruit breeders and 60 years. The UADA Fruit Breeding Program is large, complex, and works on multiple crops. A recent program initiative has been the introduction of modern tools for breeding approaches and data collection and management. This talk will outline the process for developing a molecular breeding pipeline for blackberry (Rubus subgenus Rubus Watson) and muscadine grape (Muscadinia rotundifolia) and outline how these approaches benefit program progress. Additionally, advances in data collection techniques such as digital evaluations using an application and development of barcoding systems for streamlining processes and minimizing error will be described.

The U.S. Department of Agriculture (USDA) Agriculture Research Service (ARS) has operated a European pear (Pyrus communis) scion breeding program for over a century. The breeding program started in the early 1900s by Merton B. Waite in the Washington D.C. area with the primary objective to develop host resistance to fire blight, a devastating disease caused by Erwinia amylovora. The USDA pear breeding program has continued this effort throughout its history, spanning over six generations of breeders and two cooperative research programs in Michigan and Ohio. The program has released ten named pear varieties, with the first one, 'Waite,' being released in 1938 and the most recent, 'Bell,' in 2022. In this presentation, we discuss the program's history by detailing each generation of breeder(s) aims, their parental selection, and releases. In addition, we present corrected pedigrees for important breeding lines and the releases. Lastly, we present the current objectives of the program, the pedigree complexity of newly generated populations, and the overall success of the program’s primary breeding goal – fire blight resistance.

Interspecific hybrid grapevine cultivars have been developed to expand grape cultivation into cold-climate areas. Cold weather events can lead to bud death and trunk injury which reduce yields and can result in plant death. Phenotyping cold hardiness is challenging, and developing a standardized phenotypic protocol would enable efficient evaluation of University of Minnesota grape breeding germplasm. The objective of this study is to utilize differential thermal analysis as an assay to quantify the low temperature exotherm response of grapevine buds. We phenotyped 28 varieties and advanced breeding selections from October 10th, 2023 through March 20th, 2024. Commercial cultivars (e.g. Marquette, Itasca, Frontenac) and breeding selections (wine grape, table grape, and rootstocks) were sampled weekly or bi-weekly based on availability of plant material. Differences in acclimation and deacclimation patterns between time points were observed in the low temperature exotherm readings, indicating that there may be differences in the genetic mechanisms for cold hardy responses. After the coldest day of the season, January 14, 2024, which had a low of -23°C, the temperature at which 50% of the buds would die, or LT50, for ‘Marquette’, ‘Itasca’, and ‘Frontenac’ were -29.7 °C, -30.9 °C, and -30.5 °C, which is consistent with field observations. The LT50s were rated at lower temperatures than the ambient air temperature, thus all genotypes were able to survive the weather conditions for this cold event. Future analysis aims to utilize K-means cluster analysis to determine groups that differ in responses to winter fluctuations in temperature and to determine the genetic controls for these responses.

The genetic mechanisms controlling fruit morphology in watermelon is not fully understood. Only one candidate gene, ClSUN25-26-27a (Cla011257), has been identified as a significant contributor to the ovary and fruit shape. ClSUN25-26-27a is a member of the SUN gene family, which has been extensively studied in relation to fruit morphology in tomatoes. In tomato, the effect on fruit shape facilitated by this gene is detectable during the early stages of fruit development, with the cell patterns established pre-anthesis. In watermelon, three alleles of ClSUN25-26-27a are known to be associated with ovary and fruit shape variation: the wild-type, a SNP, and a 159bp deletion in the 3rd exon. This study aims to determine the effect of the novel allelic variation for ClSUN25-26-27a on ovary and fruit shape. Four novel alleles have been identified and sequenced in the coding region of ClSUN25-26-27a across three Citrullus species. Marker assisted backcrossing was used to introgress the different alleles into a common genetic background. The NILs were phenotyped in the field to determine the effect of the novel alleles on ovary and fruit shape. Ovary length and width were measured four days pre-enthesis, at anthesis, and four days post-anthesis and used to calculate the ovary shape index (OSI). Mature fruit was also phenotyped using Tomato Analyzer. One of the novel alleles was significantly associated with ovary and fruit shape. These findings contribute to the understanding of the important SUN gene family and the genetic mechanisms contributing to watermelon fruit shape. Future research will determine the gene expression patterns of the different alleles and the effect of the alleles on the cell number or cell size in watermelon.

Mangos are the fifth most consumed fruit in the world (World Atlas). The top five mango producers include India, China, Indonesia, Pakistan, and Mexico (World population). Puerto Rico is the largest U.S. mango producer (2,666 acres), followed by Florida (2,455 acres), Hawaii (497 acres), California (328 acres), and Texas (10 acres). There are thousands of mango cultivars worldwide and the development and selection of new cultivars is ongoing. However, relatively few cultivars have a combination of information on their phenology, metabolomic profiles, consumer preferences, and postharvest handling. Describing and linking these cultivar evaluations and attributes may improve marker-assisted breeding efforts to develop and select for superior mango flavor, aroma, and nutritional value, improve understanding of hedonic consumer preferences, and result in improved postharvest handling and processing of mango. For example, ‘Glenn’ mango is a moderately vigorous tree with an upright open canopy that is generally dormant from November through December-January that flowers during February-March in response to warming ambient temperatures and is harvested during June-July. Historical descriptions are that it is a fruit of excellent eating quality with a rich, aromatic (pineapple notes) flavor, low fiber, and sweet pulp. This is borne out by the nonvolatile physiochemical characteristics of the cultivar including an average TSS of 15.93, TA of 0.65, and TSS/TA ratio of 24.41, with high concentrations of fructose, glucose, isocitric acid, and ketoglutaric acid. Defining nonvolatile flavor constituents from partial least-squares discriminant analysis for ‘Glenn’ mango were fructose, glucose, sucrose, isocitric acid, ketoglutaric acid, malonic acid, and gallic acid whereas defining volatile aroma constituents included ten esters (e.g., ethyl acetate, ethyl butanoate, and ethyl octanoate) that have floral, citrus, sweet, fruity, pineapple, and coconut notes. Results from a consumer sensory (taste, flavor, texture, fibrousness, juiciness, etc.) acceptance study indicated consumers like ‘Glenn’ mango because of its sweetness, tropical flavor, low fiber content, and juiciness, bearing out historical descriptions of this fruit. More detailed metabolic biosynthesis mapping linked flavor precursors and intermediates to the constituents responsible for flavor and aroma of ‘Glenn’. Postharvest evaluations reported ‘Glenn’ was moderately susceptible to hot water treatment injury, significant anthracnose incidence, only slight chilling injury (if stored below the 13°C recommended temperature) and could be stored for at least 3 weeks.

Since the 1920’s, Oregon State University (OSU) and the United States Department of Agriculture (USDA) Horticultural Crops Production and Genetic Improvement Research Unit have cooperated in the public breeding and development of small fruit cultivars to support Pacific Northwest (PNW) production. Together, the PNW states of Oregon and Washington have significant berry production with 152,407 metric tons of blueberry (Vaccinium spp.), 24,494 metric tons of red and black raspberry (Rubus idaeus; R. occidentalis), 9,525 metric tons of blackberry (Rubus spp.), and 6,804 metric tons of strawberry (Fragaria x ananassa) in 2022. Processed berries are the primary regional market, with fresh market production a lesser but still important driver for small farms. To continue to improve regional production of high-quality fruit, cultivar development has been a top tier research priority for PNW berry commodity commissions over the past decade. The cooperative breeding program has a continual germplasm improvement cycle that includes plant material in all stages of development, from seedlings, observational and replicated field trials, grower trials, and cultivar releases. After seedling evaluation, promising advanced selections of strawberry, blueberry, blackberry, red raspberry, and black raspberry crops are assessed at the OSU North Willamette Research and Extension Center in Aurora, Oregon. The USDA and OSU cooperative breeding program, in collaboration with Washington State University, has a uniquely strong focus on developing machine harvestable small fruit cultivars. Over 20 cultivars have been released with a value to PNW industries of over $450 million in the last ten years. ‘Tillamook’ strawberry, and ‘Black Diamond’ and ‘Columbia Star’ blackberry lead the acreage in Oregon and were developed by the program. More than 50 berry cultivars have been released since 1942 exclusively by the USDA with another 16 jointly-released with other agricultural universities and international corporations. This presentation will outline the cooperative breeding framework, discuss breeding priorities, and highlight new and upcoming cultivar releases.

Hybrid grapevines (Vitis spp.) grown in cold climate regions have fruit chemistries which do not adhere to the standard ranges of European wine grapes (Vitis vinifera L.) that many consumers may be accustomed to. The variation in fruit chemistry observed in hybrid grapevines is driven by a combination of genetics of parent material, which often builds on wild Vitis species, and the environmental conditions of production, which are often characterized by low heat accumulation and limited duration of growing season. Characterizing the genetic basis of fruit attributes enables breeders to understand and improve the relative quality of interspecific grapevines for future cultivar development. To address this knowledge gap for breeders, an incomplete diallel population of interspecific hybrid grapevines was assessed over a period of three years. Fruit chemistry (total soluble solids, pH, total acidity, glucose, fructose, malic acid, tartaric acid, citric acid, and yeast assimilable nitrogen content) and berry mass were examined at three distinct time points within each growing season to yield a total of nine phenotyping events. Best linear unbiased predictors (BLUPs) calculated from multi-year phenotype data were then interrogated via GWAS analysis to identify significant marker-trait associations. Chromosomes 16, 6, and 17 were noted to have the highest number of associations observed. To further understand the specificity of observed loci, gene annotation was conducted to reveal several important genes potentially related to the phenotypes. Due to the quantitative nature of fruit attributes, genomic selection strategies were explored to assess their accuracy for improving population performance in a systematic manner. Cumulatively, this analysis provides important information regarding the role of genetics in major fruit traits of interspecific cold hardy grapevines, regions of interest for fine mapping, and strategies for genomic selection. These analyses contribute towards the goals of improving breeding efficiency and selection accuracy to reduce generation timeline in grapevines.

Peach is an introduced crop with a relatively short production and breeding history in the U.S. The peach industries have been facing declines and challenges in both production and breeding activities over the past decades. Understanding of the statuses and issues facilitates gaining insights and finding solutions. This presentation is to provide an overview of U.S. peach production and breeding, including trends, issues, and prospects. Both U.S. peach acreage and production are declining, but market values increasing. Public peach breeding programs were established at the early time and helped establish considerable production in many states. But most of them have been terminated, phased out, or de-emphasized, largely due to declining production and economic impact. Taken into consideration all factors, visionary peach horticulture research and breeding solutions for some cost-related and yield-limiting production issues are essential for profitable and sustainable peach production in the future.