ASHS 2025 Conference

A forum for discussion of potential collaborations with regards to plant growth and culture – i.e. propagation, root growth, water management, weed control, PGRs, plant nutrition, etc.

Blueberries (Vaccinium spp.) exhibit a high degree of asynchrony during flowering, fruit set, and ripening. Fruit pigmentation is highly dependent on direct solar radiation, resulting in significant differences between sun-exposed and shaded berries within the same cluster. This study evaluated the effect of two plant growth regulators (PGRs), abscisic acid (ABA) and methyl jasmonate (MeJas), on fruit coloration and firmness under in vitro conditions. Clusters from two cultivars, ‘Duke’ and ‘Brigitta’, were collected at the green berry stage, two weeks before the expected start of commercial harvest in the 2024–25 season. Half of the clusters were taken from the outer canopy (sun-exposed) and half from the inner canopy (shaded). In the laboratory, clusters were placed in Falcon tubes with their twigs immersed in one of six solutions: (1) water (Control 1), (2) sucrose (Control 2), (3) ABA 500 ppm sucrose, (4) ABA 1000 ppm sucrose, (5) MeJas 0.1 mM sucrose, and (6) MeJas 1 mM sucrose. The samples were maintained in a growth chamber under controlled temperature (22 °C) and photoperiod (16 h light at 70 µmol/m²/sec). Fruit were evaluated at 3, 6, and 9 days post-treatment for coloration (percentage of blue fruit) and firmness (g mm⁻¹). ABA treatments significantly accelerated fruit coloration in both cultivars. In ‘Duke’, ABA-500 and ABA-1000 reached 80% and 100% blue fruit by day 6, respectively, compared to

Many traditional European cider cultivars are known to have biennial bearing tendencies and growers have reported that conventional thinners such as 1-naphthaleneacetic acid (NAA) and 6-benzylaminopurine (6-BA) are ineffective. The goal of this two-year study is to determine the efficacy of plant growth regulators (PGRs) on traditional European cider cultivars in reducing biennial bearing and improving juice and cider quality, while also maintaining sufficient yield to ensure profitability. The chemical thinners used in this study were applied with a backpack sprayer and consisted of the lowest and highest labelled rates of NAA (PoMaxa; Valent BioSciences LLC, Libertyville, IL) and 6-BA (MaxCel; Valent BioSciences LLC, Libertyville, IL) mixed with 1-naphthyl methylcarbamate (Carbaryl; Sevin SL; Loveland Products Inc, Greeley, CO). The chemical thinners were applied to the high-tannin cider cultivars, ‘Binet Rouge’, ‘Chisel Jersey’, ‘Dabinett’, ‘Harry Masters Jersey’, and ‘Porter’s Perfection’. The experiment was conducted at the Cornell research orchards in Ithaca and Lansing, NY, as well as commercial orchards in Walden, Lyndonville, and Trumansburg, NY. Each site was a fully replicated (n = 5) randomized complete block design. Preliminary data found that chemical thinning reduced crop load between 24% and 62% (measured as the total number of fruit per tree) and increased individual fruit weight (measured in grams) between 24% and 70%. Additionally, chemical thinning increased soluble solids concentration in the juice (measured in degrees Brix) between 6% and 29% and increased titratable acidity (measured in grams/liter) between 9% and 29%. These results demonstrate that PGRs can be effectively used to manage crop load for European cider cultivars. A second field season is planned for 2025.

Photosynthesis, the process by which light is converted into chemical energy, occurs in chloroplasts and involves two photosystems (PS II and PS I) connected by the cytochrome b6f complex. PS II is responsible for water splitting in oxygenic photosynthesis and is composed of a dimeric core and peripheral antennae. These antennae regulate excitation pressure under varying light conditions, preventing damage to PS II. In high-light environments, dissociation of the antennae is crucial for optimizing light harvesting and enabling self-repair of PS II. Phosphorylation of core proteins, particularly at the Thr2 residue in PsbA (D1) and PsbD (D2), plays a key role in antenna regulation and PS II repair. However, the mechanisms underlying phosphorylation-dependent disassembly of PS II are not well understood. In this study, we generated mutated PsbA and PsbD genes with alanine substitutions at the Thr2 phosphorylation site. These mutated genes were introduced into the chloroplast genome via particle bombardment, and homologous recombination was used to replace the native genes. Characterizing plants with these mutations will provide insight into the role of phosphorylation in the disassembly of PS II, a process crucial for light-harvesting efficiency and repair. This work aims to enhance our understanding of photosynthetic regulation and inform strategies for improving crop efficiency.

Gillenia stipulata, commonly known as Wester Indian Physic, is an ornamental herbaceous perennial in the Rosaceae family native to the Midwest and Eastern North America. Ethephon has been previously shown to affect plant growth, development and early flowering in apple seedlings. In the present study, interaction of ethephon and light quality on G. stipulata plant growth and development was examined. Plants were grown from seed purchased from Prairie Moon Nursery (Winona, MN) and when 4-5 leaves had been initiated, seedlings were treated with 0 (Control), 500 ppm, 1000 ppm, or 2000 ppm Florel (Monterey Lan

Pre-harvest fruit drop (PFD) causes significant yield losses in commercially valuable apple cultivars like 'Honeycrisp'. Ethylene, the master regulator of various fruit ripening traits in climacteric fruits, accelerates pre-harvest fruit drop. While ethylene inhibitors such as aminoethoxyvinylglycine (AVG) effectively reduces PFD, it can negatively impact fruit color development, a process also regulated by the plant hormone ethylene. To address this trade-off, we evaluated various plant growth regulators (PGRs), such as Accede (1-aminocyclopropane-1-carboxylic acid (ACC)-10%), Motivate (ethephon-21.7%), ReTain (AVG-15%) and their combinations, in ‘Honeycrisp’ apples over two consecutive years (2023

Approximately 3-5% of perennial orchard trees are replanted annually. Bearing fruit on newly planted orchard trees is undesirable because fruits are strong carbohydrate sinks and compete with shoot growth, and thus limit early growth of orchard trees to fill their space. Therefore, manual removal of flowers and fruitlets from newly planted trees has been practiced. In almond, leaving nuts on young trees cannot just limit vegetative growth but also serve as harboring site for navel orange worm. Therefore, removal of flowers and fruitlets/nutlets via spray application of chemical thinners would be highly desirable to aim tree growth and reduce manual labor cost for tree defruiting. In a series of experiments in nectarines, almonds and walnuts in California, we investigated the effects of the application of ACC alone or in combination with S-abscisic acid (S-ABA), 6-benzyladenine (6-BA) on flower and fruitlet/nutlet removal. Results indicated that ACC by itself at 450-600 mg/L or in combination with 300 mg/L S-ABA or 400 mg/L 6-BA can effectively defruit young orchard trees and reduce manual labor cost. No phytotoxicity was observed in any of the trials.

‘Ambrosia’ is an emerging apple cultivar recently introduced from British Columbia and knowledge of ripening and preharvest physiology is limited in the mid-Atlantic region. ‘Ambrosia’ must meet minimum quality and color marketability standards in the US though it requires a high temperature differential for full color development and has a short harvest period. Plant growth regulators, such as aminoethoxyvinylglicine (AVG) and 1-methylcyclopropene (1-MCP), can alter preharvest fruit drop, maturity and quality by hindering ethylene biosynthesis and perception, respectively. AVG has historically been used at several rates by mid-Atlantic growers with variable cultivar specific impacts. The objective of this study was to characterize and compare the effects of AVG and 1-MCP on preharvest fruit drop and crack, ethylene production, fruit physicochemical parameters, skin color, and transcript accumulation of ethylene and anthocyanin-related genes in 'Ambrosia' apples throughout on-the-tree ripening over two production seasons. Four treatments were established and applied based on manufacturer’s recommendations: full-rate AVG (Retain), half-rate AVG (Retain), 1-MCP (Harvista) and a control. Fruits were harvested at three maturity stages: 1 week before the anticipated commercial harvest (1WBCH), at the anticipated commercial harvest (CH), and one week after CH (CH 1). Our results showed that both AVG and 1-MCP treatments significantly reduced preharvest fruit drop and crack with respect to control fruit. While full-rate AVG treatment showed the most significant decrease in ethylene production and exhibited the greatest downregulation of ethylene biosynthesis and perception-related gene expression, it also negatively impacted red color and anthocyanin biosynthesis related gene expression and reached minimum 50% skin blush one week later than the other treatments. Half-rate AVG and 1-MCP treatments displayed an intermediate behavior between full-rate AVG and control fruit, delaying fruit maturity and the associated gene expression when compared to control, but without sacrificing skin blush development. This study contributes to understand how preharvest ethylene regulator treatments influence ‘Ambrosia’ apples grown under the mid-Atlantic environmental conditions.

Ethylene plays a significant role in flower and fruitlet abscission. The use of compounds that generate ethylene for chemical thinning of fruit trees has been in the focus of research for decades. 1-aminocyclopropane-1-carboxylic acid (ACC) is a naturally occurring precursor to ethylene and has recently been registered as a chemical thinner in the US and elsewhere for stone fruit and apple. Ethephon has also been evaluated for chemical thinning of peaches but phytotoxicity and inconsistency in efficacy has hindered its commercial use. With the recent registration of ACC for chemical thinning of peaches, questions arose if similar efficacy can be achieved with the use of ethephon. The objective of the study reported here was to compare thinning efficacy and phytotoxicity of ACC (300 mg/L) and ethephon (428 mg/L; molar equivalent to 300 mg/L ACC) when used in peaches. A field experiment was conducted in Red Top peach variety in Oregon where the two compounds were sprayed to different set of trees every day from pink bud to petal fall to evaluate the effect of daily weather conditions on flower abscission. Phytotoxicty was also recorded in the experiment. ACC and ethephon showed similar thinning pattern throughout the flowering time. While no phytotoxicity was observed for ACC, severe leaf drop and gummosis occurred in the ethephon treatments. The presentation will discuss the potential reasons for the efficacy and difference in level of phytotoxicity between the two compounds.

Our objective was to quantify prohexadione-calcium foliar spray or substrate drench applications to control growth of two perennial ornamental grass taxa. On 6 June 2024, 38-cell liner trays (126-mL individual cell volume) of Andropogon gerardii ‘Red October’ and Miscanthus sinensis ‘Fire Dragon’ were received from a commercial propagator. Liners were transplanted with one plant per 19.7-cm-diameter container (1.7 L volume) filled with a commercially available bark-based substrate comprised of (by vol.) 56.5% aged pine bark, 34.8% Canadian sphagnum peatmoss, and 8.7% perlite, dolomitic limestone, a nutrient starter charge, and a wetting agent. Plants were grown at bench-level in a glass-glazed greenhouse under supplemental and day-extension lighting provided by 1000-W light-emitting diode lamps from 0600 to 2200 HR (16-h photoperiod) with an air temperature set point of 20 °C. At 7 d after transplant, 10 single-plant replicates of each taxa were treated with a solution containing prohexadione-calcium and a water conditioning agent. Plants received either a foliar spray (vol. 0.2 L·m–2) solution containing deionized water (0 mg·L–1; untreated) or 250, 500, 750, 1,000, or 2,000 mg·L–1 prohexadione-calcium or a substrate drench of 296-mL aliquots of solution containing 0, 125, 250, 500, or 1,000 mg·L–1 prohexadione-calcium. At eight weeks after treatment, plant height, plant diameter, and shoot dry weight (SDW) were determined for all plants, and root dry weights (RDW) were determined for a sub-sample (n = 5) of each taxa from each substrate drench treatment. Foliar spray applications of 125 to 2,000 mg·L–1 prohexadione-calcium did not affect growth of either perennial ornamental grass taxa. Substrate drenches were effective in controlling growth of each perennial ornamental grass taxa although the magnitude of response varied among taxa. For example, compared to untreated plants, plant height, plant diameter, SDW, and RDW of ‘Red October’ Andropogon drenched with 125 to 1,000 mg·L–1 prohexadione-calcium decreased by 20% to 57% (19.7 to 55.9 cm), 0% to 43% (7.8 to 33.4 cm), 3.6 to 28.9 g (10% to 81%), and 10.4 to 28.5 g (27% to 74%), respectively. This research demonstrated substrate drench applications of prohexadione-calcium to be effective for controlling growth, while further research is warranted to determine optimal concentrations for foliar spray applications. We suggest substrate drench applications of 125 to 500 mg·L–1 prohexadione-calcium as an initial range for trials to control growth of ornamental perennial grasses.

The propagation of ornamental woody nursery liners (young plants) is primarily through stem cuttings to maintain genotypic and phenotypic uniformity. The application of rooting hormones is common practice in stem cutting propagation to hasten, promote uniformity, and enhance the quality of adventitious rooting. Rooting hormones are traditionally applied by dipping cuttings into solutions or powders. However, these methods increase labor costs, cutting stress, and opportunities for contamination. Foliar applications of rooting hormones would improve production efficiency, reduce cutting contamination and stress, and allow for multiple hormone applications after sticking. Thus, there is a critical need to identify the optimal rates of foliar rooting hormones to improve and maximize adventitious rooting in woody nursery taxa. Therefore, this study aimed to quantify the impact of foliar rooting hormones on root growth and development of ornamental woody nursery cuttings. Unrooted stem cuttings of four ornamental nursery taxa were obtained from commercial nurseries and individually inserted into 6.4-cm diameter containers filled with a propagation substrate. Cuttings were placed in a diffused glass-glazed greenhouse under a propagation environment of fixed 4-mil clear construction film. The greenhouse was set at 20 °C air temperature, 80% relative humidity, and ambient daylight supplemented with ≈120 µmol·m–2·s–1 delivered from light-emitting diode arrays from 0600 to 2200 hr. At 1 d after sticking, cuttings were sprayed with a solution containing clear tap water and 0, 500, 1,000, 1,500, 3,000, or 6,000 mg·L–1 20% indole-3-butyric acid (IBA) at a volume of 1.89 L·m–2. After 42 d, data was collected including callusing and rooting percentage, stem length and caliper, leaf area, and shoot and root dry mass. In general, increasing IBA foliar application concentration improved rooting success and uniformity to different magnitudes among species. For example, rooting percentage of Chamaecyparis increased by 67% as foliar IBA concentrations increased from 0 to 6,000 mg·L–1 IBA. The results of this study determined the optimal rates of foliar IBA application across an array of woody taxa to hasten adventitious rooting and improve quality for ornamental woody nursery liner production.

A high-quality containerized culinary herb is one that is proportional to its container with a compact growth habit and stems or leaves that are not excessively elongated. However, chemical plant growth regulators (PGRs) used to modify plant growth, increase branching, or reduce stem elongation are not labeled for use on culinary herbs. A novel option for reducing stem elongation could be exposure to night-interruption (NI) ultraviolet (UV) radiation. Therefore, our objectives were to 1) quantify the influence of UV-A radiation on the growth, stem elongation, and relative chlorophyll concentration of containerized spearmint (Mentha spicata) and Greek oregano (Origanum vulgare var. hirtum) and 2) determine the most effective duration and sequence of exposure. Rooted cuttings were transplanted into 15-cm containers and placed in a greenhouse at 23 °C and under a 16-h long-day (LD) provided by LED supplemental lighting (SL) or under a 9-h short-day (SD) and 6-h of NI lighting providing 385 nm of UV-A radiation at an intensity of 20 µmol∙m–2∙s–1 for 4 weeks. The 10 treatments included: LD entire time, LD 2 week-UV 2 weeks, LD 1.5 weeks-UV 2.5 weeks, LD 2 weeks-UV 2 weeks, LD 2 week-UV 1 weeks-LD 1 week, UV entire time, UV 2 weeks-LD 2 weeks, UV 2.5 weeks-LD 1.5 weeks, UV 2 weeks-LD 2 weeks, or UV 2 week-LD 1 week-UV 1 week. Exposure to SD UV-A NI for 4 weeks, resulted in a ≈ 25 and 29% reduction in height of Greek oregano and spearmint, respectively. Furthermore, when LDs were the last treatment spearmint plants received, they had a higher chlorophyll content than those exposed to UV-A. Our results indicate that UV-A NI lighting for spearmint and Greek oregano may be an option for height control in controlled environments.

Greenhouse substrates are soilless mixes formulated by blending organic and inorganic components at varying proportions. Substrate properties are known to influence the efficacy of plant growth regulators applied as a substrate drench. Ethephon is a plant growth regulator used in floriculture production to control stem elongation, increase lateral branching, and manipulate flowering. Ethephon substrate drenches have been shown to control growth in annual bedding plants and herbaceous perennials; however, there is a lack of research examining how substrate composition influences the efficacy of ethephon substrate drenches. Therefore, the objective of this research was to evaluate ethephon drench efficacy in peat-based substrates amended with perlite, aged pine bark, or wood fiber. Lantana (Lantana camara L. ‘BandoleroTM Pink’ and ‘New Gold’) were transplanted into 15.2-cm containers filled with one of six peat-based substrates amended (by vol.) with 20% or 40% perlite, aged pine bark, or wood fiber. After 10 d, eight single-plant replicates received a drench of 150 mL aliquots of solution containing 0, 25, 50, 75, 100, or 200 mg·L–1 ethephon. Plants were grown in a glass-glazed greenhouse for 5 weeks after drench before growth data, including plant height, plant diameter, shoot dry weight (SDW), and root dry weight (RDW) were determined. Increasing concentrations of ethephon decreased plant height, plant diameter, SDW, and RDW of both cultivars of lantana. Substrate components and formulation had varied effects on plant growth. For example, in Expt. 1, plant height was unaffected by formulation but the component × concentration interaction was significant. When substrates were formulated with perlite, aged pine bark, or wood fiber plants were 23% (3.9 cm), 13% (2.0 cm), and 18% (3.1 cm) shorter, respectively, as concentrations increased from 0 to 200 mg·L–1 ethephon, compared to untreated plants. In Expt. 2, neither component or formulation significantly influenced plant height, and when drenched with 200 mg·L–1 ethephon plant diameter was 42% (15.8 cm) less than untreated plants. In Expt. 1, SDW was not influenced by formulation but the component × concentration interaction was significant. For instance, compared to untreated plants, SDW of plants grown in substrates containing perlite, aged pine bark, or wood fiber were 42% (3.8 g), 23% (1.7 g), and 35% (2.7 g) smaller, respectively, as concentrations increased from 0 to 200 mg·L–1 ethephon. Overall, ethephon substrate drench efficacy was not reduced by the incorporation of perlite, pine bark, or wood fiber in peat-based substrates.

Polyethylene glycol (PEG) is widely used to simulate drought stress in plant germination studies due to its ability to induce osmotic stress without being absorbed by plant tissues. This study investigates the effects of PEG-induced drought stress on the seed germination of various ornamental plant species, including Celosia argentea, Petunia hybrida, Rudbeckia hirta, Salvia splendens, and Zinnia elegans. Seeds are treated with different concentrations of PEG-6000 (0%, 5%, 10%, and 15%) to mimic varying levels of water deficit. Germination trials are conducted under controlled environmental conditions using LED lights with a 16/8-hour photoperiod to simulate light/dark conditions, and an optimum temperature of 70-75°F (21-23°C) to support ideal germination and seedling growth. Current seed research trials are underway with aims to evaluate germination-related traits under stress, including germination percentage, mean germination time, germination rate, and seedling vigor. These traits are used to assess the early-stage drought tolerance of ornamental plants. Understanding how different species respond to water stress at the germination stage is crucial for the ornamental plant industry, as it supports the selection and development of more resilient varieties suited for landscapes and markets increasingly affected by water scarcity.