ASHS 2024 Conference

Sales of compact vegetable bedding plants for the home-gardening market segment are increasing. However, production guidelines for these new crops are limited. Our objective was to assess the effect of fertilizer use and controlled-water deficit (CWD) on plant growth during production, and after-production effects on fruit yield. ‘Siam’ tomato and ‘Basket of Fire’ pepper plants were grown in a greenhouse for 4 and 6 weeks, respectively, using 10-cm containers. Half of the plants received a water-soluble fertilizer once a week, and the other half were irrigated with tap water only, relying on the starter fertilizer charge in the substrate (EC = 0.9 mS·cm−1). Plants were irrigated when the substrate volumetric water content (VWC) reached 0.15, 0.30, 0.45, or 0.60 m3·m–3. After the experiment, plants were transplanted into 20-cm containers, top-dressed with controlled-release fertilizer (CRF), and grown for another 10 weeks to evaluate carryover treatment effects. Plants that did not receive fertilizer were shorter and had a lower shoot dry mass (SDM) than those that were fertilized, regardless of species. Shoot height of tomato followed a quadratic trend in response to CWD, which peaked at 0.45 m3·m–3, whereas SDM linearly increased with increasing VWC. No growth responses to CWD were measured for pepper. However, plants of both species that did not receive fertilizer looked chlorotic and had a lower chlorophyll concentration than those that were fertilized (15 and 32 µmol·m–2 for tomato and 15 and 27 µmol·m–2 for pepper, respectively). Plant greenness increased after applying CRF, suggesting that applying fertilizer right before shipping could increase quality of these plants when grown with limited or no fertilizer to control growth. After the carryover phase, differences in plant growth were maintained, and differences in yield was measured between fertilized and non-fertilized plants (56 and 48 fruits for tomato and 153 and 112 fruits for pepper, respectively). Our results show that growth and yield of compact tomato and pepper plants are affected to a larger extent by fertilizer use than by substrate VWC.

The Assessment of Plant Growth Regulators on Sweetpotato Slip Propagation - Kerington Bass
Effects of a Cytokinin-Containing Biostimulant Applied at Different Phenological Timings on Almond (Prunus dulcis) Yield - Orlando Tapia
Preharvest Abscisic Acid (S-ABA) Spray Application Promotes Fruit Ripening, Color Development and Regulates Quality in Early Maturing ‘Yoho’ Persimmon - Mahmood Ul Hasan
The Application of a Cytokinin B-Mo-based Product Influences the Source-to-Sink Dynamics and Non-Structural Carbohydrate - Mayra Toro Herrera
PGR applications to reduce HLB-associated preharvest fruit drop in Sweet Orange - Tripti Vashisth
Ethephon Effect on Blooming of Three Southern Highbush Cultivars - Lilian Carcamo
Development of a Tissue Culture Approach for Doubling the Ploidy Level of Southern Highbush Blueberry Varieties - Emily Walter

Producing sweetpotatoes involve several phases presenting unique challenges, most notably during transplanting. Sweetpotato slips, used for asexual reproduction, have non-uniform characteristics, making transplanting difficult. Additionally, the transition from a greenhouse to a field condition poses environmental risks and challenges, resulting in low transplant survival rates. A high slip mortality rate creates economic and logistical problems for producers. Plant growth regulators (PGRs) have been found to induce lignification or thickening of cell walls, which can alleviate environmental stresses in other crops; however, their impact remains unexplored in sweetpotato slips. Therefore, a study at Mississippi State University was conducted with the primary goal to enhance sweetpotato slip quality and improve transplant establishment rates. The study involves two greenhouse trials to identify the most effective PGR types and concentrations, and two histology trials to illustrate the effects of PGRs on sweetpotato slip lignin and cell wall. The greenhouse trials utilize a randomized complete block design to assess four different PGR types and thirteen concentrations on three replications of sweetpotato slips with 38 subsamples per treatment per replication. Data on plant height, stem diameter, number of nodes, SPAD, leaf area, and dry weight and fresh weight of the slips and roots were collected to determine the effects of PGRs on the plants. The histology trials included the same PGR treatments and concentrations to the slips. The slips were then collected, cross-sectioned, stained, and evaluated and measured under a microscope. The study proved that PGRs do have an effect on sweetpotato slips, by altering plant height, dry weight, and fresh weight, while not impacting the number of nodes. Thickening of the cell wall was also observed in slips treated with certain PGRs and it is hypothesized that this thickening of cell walls can contribute to reduced slip mortality when transplanting greenhouse produced slips to the field.

Almond (Prunus dulcis) is one of the most important crops in California. This commodity represented an economic impact of over 3.5 billion dollars for the state in 2022. During that year, 1,630,000 million planted acres were reported. In 2023, this number dropped by 74,000 acres, continuing the trend of decline due to numerous challenges that the industry has been facing. These include volatile prices, high input costs, reduced water allocations, climate unpredictability, and high temperatures during key phenological timings. The almond crop is highly sensitive to environmental factors, and photosynthetic rates can significantly decrease when temperatures reach 94F, heat levels are easily reached during the hot summer months in California’s production areas. To this matter, significant contributions are needed to support the industry. There are over 700 peer-reviewed scientific publications that evidence the benefits of using biologicals, which include plant biostimulants (PBS), in agriculture. It has been shown that season-long exogenous applications of cytokinin-containing PBS can support higher marketable yields. It is important to understand the physiological timings in which these applications have the most impact, in terms of maximizing the yield and quality potential. In 2023, a randomized complete-block design (RCBD) study was conducted on 5th leaf Var. Nonpareil in California’s Central Valley. The objective was to evaluate the yield and quality effects of an application of X-CyteTM, a 0.04% cytokinin-containing biostimulant registered for use on almonds in California, at different standalone phenological timings. These included early bloom, full bloom, petal fall, may spray, and hull-split. The trial consisted of six four-tree replications per treatment. Yield and quality data were subjected to a one-way ANOVA using IBM® SPSS® Statistics, and means were separated using Tukey’s HSD. The standard grower practice (SGP) produced 1801.5 marketable pounds of kernel meat per acre. X-Cyte™ treatment yields of 1845.16, 2140.16, 2215.66, 2137.67, and 2318.33, were observed for early bloom, full bloom, petal fall, may spray, and hull-split timings, respectively. Statistically significant differences were observed (p-value: 0.003). The hull-split and petal fall timing applications represented the higher yield increases (516.8 and 414.2 lbs/A, respectively) overall, compared to the SGP. It has been documented that taking place at these timings are key phenological stages deemed as major contributors to the components of yield: fruit set and nut fill. Significant differences in kernel size were not observed (p-value: 0.549). These findings further support and help fine-tune the use of biologicals and PBS in agricultural production systems.

Persimmon is an important fruit crop gown all over the world due to its unique fruit taste and nutritional quality. The skin color is one of the key attributes in persimmon fruit to determine the harvest maturity. Poor color development in early maturing cultivars causes losses to the growers. The present study was aimed at evaluating the effects of preharvest S-ABA spray application on advancing color development and improving fruit quality at harvest. ‘Yoho’ persimmon trees grown in Western Australia were sprayed with S-ABA (0, 25, 50, 75 mg L-1) two weeks before anticipated harvest. The preharvest spray application of S-ABA showed significant increase in color indicators such as color index, a*, b*, and chroma of persimmon fruit harvested after one and two weeks of spray application. S-ABA (25 and 50 mg L-1) spray application showed significantly higher soluble solids content (SSC), and slightly reduced firmness in harvested fruit. Additionally, the 50 mg L-1 S-ABA spray application markedly increased carotenoids content in fruit harvested after one week, while fruit harvested after two weeks exhibited higher carotenoids in 25 mg L-1 and 50 mg L-1 S-ABA treatments. Moreover, the total phenolics, flavonoids and antioxidants were enhanced by S-ABA treatments as compared to control. In conclusion, the preharvest spray application of S-ABA (50 mgL-1) triggers fruit ripening sharply even after one week, while 25 mg L-1 S-ABA treatment showed significant improvement in color after two weeks of application. A single spray application of S-ABA could be employed for advancing harvest maturity, color development, and promoting overall persimmon fruit ripening quality.

Understanding the sink-to-source relationship on leafy crops offers valuable insights into optimizing resource allocation for enhanced plant growth and quality. Variations in growth rates and carbon pools across individual leaves or groups of leaves at similar developmental stages allow us to understand the plant strategies of carbon allocation and partitioning. We hypothesized that products that enhance the carbon source-to-sink relationship during leaf development can lead to increased growth and dry matter accumulation. This project aimed to determine if the exogenous application of a cytokinin and B-Mo-based product during leaf development would impact carbon source-to-sink relationship and, hence, influence plant growth and quality. The experiment was a complete randomized design with two treatments consisting of a negative control and the application of the product twice during the growing cycle. The experimental unit consisted of a deep-water culture reservoir with three lettuce plants. Destructive sampling was conducted at five sampling points. At each sampling point (n=4 per experimental run), the phenological stage was determined, and root and shoot length and dry matter, leaf length, width, area, and non-structural carbon and chlorophyll contents were measured. This data was used to estimate growth rates. Results indicate that the cytokinin and B-Mo-based product increased the number of true unfolded leaves by 1 ± 0.4 and the overall size of the lettuce head by 9%. The treated lettuce reached a marketable size four days earlier than the control treatment. Statistically significant differences were observed in the shoot and root dry matter accumulation and foliar length and width at some sampling points. Some of the growth indices indicate an increase in leaf surface area investment and enhanced conversion efficiency of assimilates into biomass in plants treated with the product. Plants exhibiting these alterations had higher sucrose and total soluble sugar content. There was a noticeable pattern of higher concentrations of non-structural carbohydrates, proteins, and amino acids in the leaves compared with the roots across all plants and treatments. Overall, our study on using a cytokinin and B-Mo-based product to strengthen the source-to-sink relationship during the development of a leafy crop provides new insights into non-structural carbohydrate metabolism and the role of CKs, B, and Mo in generating a high-quality plant in a shorter timeframe.

The Florida citrus industry has seen a steady decline in production since the arrival of Huanglongbing (HLB), or citrus greening disease, in Southern Florida in 2005. Following infection, trees experience a steady decline in health and productivity. HLB has since spread throughout all of Florida’s citrus producing regions resulting in nearly 100% infection rates in traditional field settings. Lamentably, no cure has been found for HLB, so research efforts have focused on mitigating the symptoms associated with this disease. Among the myriad of symptoms associated with HLB, the increased rates of mature fruit (preharvest fruit drop) is a major concern for growers. Not only do more fruit drop in HLB-affected trees, but fruit also begin dropping earlier in affected trees as well. This loss of mature, and potentially marketable, fruit in the months leading up to harvest represents a visual loss of revenue for the growers. The authors have previously reported that the likelihood of a fruit to drop during preharvest fruit drop is related to the size of that fruit; the relatively smaller fruit on the tree are more likely to drop during the preharvest fruit drop window. As plant growth regulators (PGRs) have had promising results in preventing fruit drop in many crop species, the efficacy of PGR applications in reducing preharvest fruit drop was evaluated. Thirty small and thirty large fruit were tagged on four 12-year-old ‘Valencia’ on ‘Swingle’ rootstock trees. Small fruit were those that were a ½ standard deviation below the average fruit size for that tree whereas large fruit were those that were a ½ standard deviation above the average. Ten of the small tagged fruit and ten of the large tagged fruit were then dipped into ProGibb® (33 ppm Gibberellic Acid [GA]), Citrus Fix® (106 ppm 2,4-Dichlorophenoxyacetic Acid [2,4-D]), or left untreated (control). Citrus Fix® improved retention in both small and large fruit whereas ProGibb® only improved retention in the large fruit. As GA prevents drop by delaying the senescence process, the lack of effect in the small fruit may suggest that they have already entered the senescence process. To further explore why the small and large fruit differ in their likelihood to drop and why they respond differently to PGR applications, additional biochemical and molecular analyses are underway.

Spring frost is the primary cause of yield reduction in southern highbush, representing a significant challenge to blueberry production in the southeastern United States. Plant growth regulators are used as aids in different agricultural industries to either advance or delay growth and development process. Ethephon influences fruit set, size, and yield and has also been used as a tool to delay bloom in order to avoid freeze damage. This study examined the efficacy of ethephon to delay flower bud growth stages in three Southern Highbush Blueberry cultivars (‘Farthing’, ‘Georgia Dawn’, and ‘Kee Crisp’). Ethephon was applied at different concentrations of 200, 400, and 800 ppm, and a control treatment water/surfactant was also included. Flower buds were visually assessed from January until March. No relevant results were found for ‘Farthing’; however, for ‘Georgia Dawn’ and ‘Kee Crisp', ethephon at 800 ppm had the highest effect on delaying blooming development compared to the control. These results suggest that ethephon might delay flower bud growth stages in Georgia Dawn and Kee Crisp, offering potential advantages in reducing susceptibility to spring chill injury.

Increased consumption of blueberries has led to a prominent rise in demand. However, Georgia blueberry production is limited by challenges including short orchard life of southern highbush (SHB; tetraploid) and fruit quality issues associated with rabbiteye (RE; hexaploid) varieties. Interspecific hybridization can bring in beneficial alleles to improve the local adaptability and fruit quality of commercial varieties. Many of the wild blueberry germplasm with valuable soil adaptability and fruit quality traits such as V. fuscatum are diploids. Heteroploid crossings between SHB and diploid wild blueberry were shown to have a very low level of success. Ploidy induction through tissue culture is promising to circumvent the ploidy barrier and improve the efficiency of wide-hybridization. The objective of this research focuses on developing a ploidy induction protocol using two SHB varieties ‘Emerald’ and ‘Rebel’. SHBs previously initiated in tissue culture, were treated with 0%, 0.02% and 0.2% colchicine. SHBs were segmented into single and double node segments and put into woody plant medium (WPM) culture media containing either 6-(γ,γ-Dimethylallylamino)Purine (2iP) or trans-Zeatin. The treatments, along with non-treated control, were grown in a growth chamber of 26°C with 16/8 day and night cycles. The number and length of new shoots were recorded 35 and 50 days after treatment (DAT). Significant longer axillary stem growth was observed in the non-treated control compared to that of colchicine-treated segments for both SHBs indicating the suppressive effect of stem growth from colchicine treatments. Several Octo- and mix ploidy-shoots of ‘Emerald’ and ‘Rebel’ were identified among colchicine-treated SHB explants after ~ 21 weeks using a flow cytometer. Both levels of colchicine treatments generated octoploids. These new synthetic octoploid blueberries will be useful to cross with SHB and RE blueberries. The established ploidy induction protocol will be utilized to double the chromosomal levels of diploid V. fuscatum species and make them cross-compatible with SHB varieties.

Multiple Modeling Approaches Reveal Temperature Dependent Germination Traits of Vegetable Varieties - Miro Stuke
Identifying Pollinators Present on Flowers of the Pawpaw Cultivars 'Sunflower' and 'Susquehanna' - Subas Thapa Magar
Characteristics of the Secondary Walls of Xylem of the Tomatoes Cultivated Under Water Deficit - Marcio Mesquita
Molecular Assessment of Heat Sensitivity in Broccoli Flowering - Thomas Bjorkman
Morpho-physiological Response of Plectranthus amboinicus under Flooding and Drought Stress - Samuel Asiedu
Effects of Paclobutrazol, Progressive-raising Temperature and Spike-truncated Treatments on Phalaenopsis Join Grace ‘TH288-4’ - Yi Chien Lu

Water stress is one of the major limiting factors of crop growth and productivity worldwide. Plectranthus amboinicus (Jamaican Thyme) is an aromatic, spicy and medicinal plant which is also valued in the pharmacological industry. Although the plant is generally known to tolerate some levels of drought, its response to sequences of different water stresses is unknown. In this study, we investigated the effect of flooding and drought on the growth and development of Plectranthus amboinicus. The treatments were regular watering (RW), flooding (FL), drought (DR), and rehydration (RH) after drought. The result showed that plant height was significantly (p < 0.001) reduced in DR and FL plants while fresh aboveground weight was increased by ca. 17.4% in FL compared to RW. Stomatal conductance and transpiration rates were higher in FL plants but reduced drastically in DR. Moreover, chlorophyll fluorometric indices including maximum quantum yield efficiency of Photosystem II (Fv/Fm) and potential photosynthesis capacity (Fv/Fo) were significantly (p < 0.001) increased in the FL but decreased in DR plants. Leaf relative water content was significantly (p < 0.01) highest in the RH followed by the RW, and the least in DR and DH. Leaf cell electrolyte leakage was significantly (p < 0.05) higher in the RH followed by the RW while FL recorded the least cell electrolyte leakage. These results indicate that Jamaican thyme regulates physiological characteristics to tolerate flooding and demonstrate that DR poses a severe threat to plant development.

Phalaenopsis is the most popular potted plant worldwide. However, its long spikes often lead to increased shipping costs and risks. This study investigates the effectiveness of varying the concentration, timing, and frequency of paclobutrazol (PP333) applications on shortening the spike of Phalaenopsis Join Grace ‘TH288-4’. Also we examine on different progressive-raising temperature promoting inflorescence development for prior anthesis, and on spike-truncated treatment optimizing flowering performance. Three experimental groups were established based on different PP333 application schedules: T2, T2T3 and T7T8 group. The PP333 concentrations used were 0, 250, 500, 750, and 1000 mg·L-1, applied as foliar sprays. The shortest spikes, measured from base to first flower, were observed in the T2 group with 750 and 1000 mg·L-1; the T2T3 group treated with 500, 750, and 1000 mg·L-1 PP333; and the T7T8 group treated with 1000 mg·L-1. These treatments resulted in spike lengths of 16.7-22.2 cm, which are 54-69% shorter than the control ones. PP333 application had minimal effects on other traits except root diameter. Subsequently, four experimental groups: G20, G25, G30, and G35 group, were set up based on different final flower induction temperature. Mature plants were applied with 750 mg·L-1 PP333 by foliar spray, after four weeks moved to a cool room as 20/18℃. Until the flower stalk bore 0-3 nodes, the G25, G30 and G35 groups were transferred to 25/20℃. While the flower stalk bore 4-5 nodes, the G30 and G35 group were moved to 30/25℃. When the flower stalk bore 6-7 nodes, the G35 group was finally cultured under 35/30℃. Half of plants were randomly selected and truncated the spikes while the first flower bud was 1-1.5cm long. The spike of the G35 and G30 were truncated on the 21st week, which took only 113 and 117 days from the day started placing at a cool room. The G25 and G20 group took 124 and 138 days respectively. The days to flowering of G35 and G30 group were less than G20 at least by 45 days. However, the flower of G35 group performed unusual and were the smallest. All flowers of spike-truncated plants were bigger than the controls under different temperatures. This study establishes a PP333 treatment and a flower induction temperature protocol, offering a strategy to effectively produce single-flowered phalaenopsis.

Quantifying Growth Control of Ornamental Millet ‘Jester’ with Ancymidol, Ethephon, Flurprimidol, Paclobutrazol, and Uniconazole Substrate Drenches - Lauren Seltsam
Controlling growth of Brunnera macrophylla L. ‘Jack Frost’ with Uniconazole Substrate Drenches or Sprays - William Rich
Uniconazole Substrate Drenches Control Growth of Buddleia Cultivars - Lark Wuetcher
Effects of Weather Conditions on the Efficacy of ACC as a Peach Thinner - Jozsef Racsko
Mode of Action and Uptake Investigations of ACC as a Peach Thinner - Jozsef Racsko
Physiological Mechanism of Silicon’s Enhancement of Drought and Heat Tolerance in Creeping Bentgrass - Xunzhong Zhang
Effect of Light Quality and Intensity on Cannabis Photosynthetic Activity - Philip Wiredu Addo
Enhancing the quality of novel greenhouse crops through dynamic LED lighting - Rose Seguin

Plant growth regulators (PGRs) are a valuable tool in the ornamental industry. Whether it is for promoting or controlling growth, PGRs give growers the opportunity to produce high quality crops in the face of their production or shipping challenges. Often, substrate drench applications provide greater growth control, require less labor, and have shortened re-entry intervals than spray applications. Current PGR recommendations for ornamental millet (Pennisetum glaucum ‘Jester’) are for spray applications; therefore, the objectives of this study were to evaluate the efficacy of different PGRs applied as substrate drenches to improve marketability and control growth of ornamental millet ‘Jester.’ Seeds were received from a commercial supplier and sown into 288-cell plug trays (5-mL individual cell vol.) filled with a pre-moistened commercial soilless propagation substrate. After 24 d, young plants of similar heights, basal diameters and culm were transplanted with one plant per 11.4-cm-diameter container filled with a commercially available peat-based substrate. At 7 d after transplant, plants received 59-mL aliquots of solution containing 0 (deionized water control),1, 2, 4, 8, or 16 mg·L–1 ancymidol, flurprimidol, paclobutrazol, or uniconazole or 25, 50, 75, 100, or 200 mg·L–1 ethephon. Plants were grown at bench-level in a glass-glazed greenhouse with an air temperature set point of 23 °C, and supplemental day-extension lighting provided by light-emitting diode lamps from 0600 to 2200 hr (16-h photoperiod) to achieve a daily light integral of ~14 mol·m–2·d–1. Data were collected four weeks after drench. For each chemical, effects of PGR concentration were analyzed independently, and means were separated using Tukey’s honestly significant differences. For all analyses, a P ≤ 0.05 was used to determine significant effects. In general, ancymidol and ethephon provided the best growth control, while flurprimidol and uniconazole were found to be inadequate for drenches at the concentrations investigated due to unmarketable plants. Paclobutrazol resulted in unmarketable plants at concentrations ≥ 1 mg·L–1. Ancymidol substrate drenches containing 1 to 16 mg·L–1 resulted in plants that were 3% to 21% shorter and 3% to 14% smaller plants, respectively, than untreated plants. Similarly, increasing ethephon substrate drench concentrations from 1 to 16 mg·L–1 resulted in plants that were 7% to 36% shorter and 27% to 41% smaller plants compared to the untreated control. Results from this study establish substrate drench recommendations for ornamental millet ‘Jester’; however, further investigations are needed to assess growth control responses of other ornamental millet cultivars.

Heartleaf brunnera (Brunnera macrophylla L.) is a popular herbaceous perennial that is often used in the landscape. With large leaves and a mounding habit, growth control is often needed during greenhouse production. Plant growth regulators (PGR) applied as substrate drenches or foliar sprays can control growth necessary to produce compact, high-quality containerized plants. Our objectives were to evaluate the efficacy and growth control provided by uniconazole substrate drenches or sprays. Rooted liners of heartleaf brunnera ‘Jack Frost’ were transplanted into containers (16.6-cm; 2.8 L) filled with a commercially formulated peat-based substrate. After 10 d, eight single-plant replicates received either a substrate drench or foliar application of uniconazole. For substrate drenches, 296-mL aliquots of solution containing deionized water (0 mg·L–1; control) or 0.25, 0.875, 1.75, 2,5, 5.5, 7.5, or 10.0 mg·L–1 uniconazole were applied across the substrate surface. For foliar sprays, 0, 2.5, 5.0, 7.5, 10.0, or 20.0 mg·L–1 uniconazole were applied at a rate of 1.89 L/ 9.29 m2. Plants were grown in a glass-glazed greenhouse at 23 °C under ambient daylight supplemented with a photosynthetic photo flux density of ≈120 µmol·m–2·s–1 delivered from light-emitting diode lamps from 0600 to 2200 HR (16-h photoperiod) to achieve a daily light integral of 14 mol·m–2·d–1. At 7 weeks after treatment, data were collected and plants were destructively harvested. In general, uniconazole significantly controlled plant height, diameter, and dry mass for each uniconazole application method. Plant height and diameter were 15% to 51% (2.2 to 7.6 cm) shorter and 22% to 40% (7.4 to 13.5 cm) smaller, respectively, than untreated plants as uniconazole drench concentration increased from 0.875 to 5.0 mg·L–1, respectively. Plants treated with 0.875 to 5.0 mg·L–1 developed 3 to 7 fewer leaves. Shoot dry mass was 39.5% lower than untreated plants as uniconazole drench concentration increased from 0.875 to 5.0 mg·L–1, respectively. For foliar applications, plant height and diameter were both reduced but to varying degrees. Plant height was reduced by 6% (~1 cm) but the greatest amount of control observed was in plant diameter which was reduced by 15 to 21% (4.8 to 7.2 cm) as concentrations increased from 5.0 to 10.0 mg·L–1. Collectively, these results indicate that drenches of 0.875 to 5.0 mg·L–1 uniconazole or foliar sprays of 5.0 to 10.0 mg·L–1 uniconazole may be used to control growth of ‘Jack Frost’ heartleaf brunnera.

The increasing diversity of butterfly bush (Buddleia × hybrida) cultivars presents new challenges for growers, particularly in adjusting plant growth retardants (PGRs) to manage plant size effectively. Therefore, the objective of this study was to evaluate uniconazole substrate drench concentrations for growth control of two popular cultivars of butterfly bush (Buddleia × hybrida). Liners of ‘Grand Cascade’ and ‘Prince Charming’ butterfly bush were individually transplanted into containers (16.5-cm; 1.7 L) filled with a commercially formulated bark-based substrate. After 10 d, eight single-plant replicates received a substrate drench of 266-mL aliquots of solution containing deionized water (0 mg·L–1; untreated) or 0.25, 0.5, 1, 2, or 4 mg·L–1 uniconazole. Plants were grown in a glass-glazed greenhouse at 20 °C under ambient daylight supplemented with a photosynthetic photo flux density of ≈125 µmol·m–2·s–1 delivered from light-emitting diode arrays from 0600 to 2200 HR (16-h photoperiod) to achieve a daily light integral of 14 mol·m–2·d–1. At 5 weeks after drench, data were collected. Plant height, plant diameter, growth index (GI), and shoot dry weights were unaffected by cultivar or cultivar × uniconazole concentration interaction but varied by uniconazole concentration (P < 0.0001); therefore, all data were pooled and analyzed by uniconazole concentration. Increasing uniconazole substrate drench concentrations effectively controlled ‘Grand Cascade’ and ‘Prince Charming’ butterfly bush plant height, plant diameter, GI, and shoot dry weights. Plant height and diameter were 16% to 32% (6.9 to 13.8 cm) shorter and 10% to 24% (6.9 to 16.9 cm) smaller than untreated plants as uniconazole drench concentration increased from 1 to 4 mg·L–1, respectively. Shoot dry mass was 24% to 34% (5 to 7 g) lower than untreated plants as uniconazole drench concentration increased from 1 to 4 mg·L–1, respectively. Overall, these results indicate that 1 to 4 1 to 4 mg·L–1 uniconazole applied as a substrate drench may be used to control growth of ‘Grand Cascade’ and ‘Prince Charming’ butterfly bush. Time to visible bud and flower was not negatively influenced by increasing uniconazole concentrations; however, growers should trial drench concentration and adjust as needed for desired market dates. Additionally, further investigations with uniconazole are warranted for other butterfly bush cultivar introductions because it is the is the preferred PGR for perennial growth control.

1-aminocyclopropane-1-carboxylic acid (ACC) is the immediate precursor of ethylene in plants. Accede SG containing ACC as active ingredient has been registered as a chemical thinner in the US for stone fruit and apple. The objective of this study was to investigate the effects of weather parameters on Accede SG efficacy. In a series of experiments in Oregon and California in the field and growth chambers, we evaluated the relationship between flower/fruitlet abscission caused by ACC and weather parameters in peaches. In field trials, ACC at 300 mgL-1 and 600 mgL-1 was sprayed on a daily basis to different set of peach trees throughout the bloom period and correlated fruit set data with daily weather parameters. From these field trials, it became apparent that flower/fruitlet abscission caused by ACC is in negative relationship with daily minimum and maximum temperatures. These findings were confirmed by greenhouse studies where increase in nighttime temperature reduced thinning efficacy of ACC. No close relationship between thinning efficacy and relative humidity was found. We created three models to predict ACC thinning efficacy using weather parameters and ACC spray concentration.

1-aminocyclopropane-1-carboxylic acid (ACC) is assumed to cause flower abscission via the ethylene pathway when used as a chemical thinner in peaches. The objectives of this study were to investigate the uptake of ACC via flower parts, and determine if ethylene is the main cause of flower abscission by ACC. In a series of field trials in Oregon, we determined that ACC is a non-mobile compound when applied as a foliar spray to peach trees. ACC does not translocate between branches and movement of externally applied ACC is very limited even between flower parts. When the ACC solution was applied via paintbrush to various parts of the flowers, it became evident that for sufficient flower thinning activity, the presence/uptake of ACC is needed through the pedicel and/or Abscission Zone tissues of the pedicel (AZ1-2). Application of ACC to the petals only, resulted in petal drop only but not in flower abscission. When evaluating the mode of action of ACC, we established a close relationship between ethylene production of the flowers and flower abscission. However, when ethylene production of the flowers was reduced with the addition of ACC oxidase inhibitors (2-picolinic acid, pyrazinecarboxylic acid) in the ACC spray solution, the flower abscission rate remained the same as in the ACC application alone. These results indicate that ethylene might not be the only factor in flower abscission caused by ACC.

Creeping bentgrass is an important cool-season turfgrass species widely used for golf course putting greens, however it experiences summer stress and quality decline in the U.S. transition zone and other regions with similar climates. Silicon (Si) may improve abiotic stress of creeping bentgrass, but mechanism of its impact on plant drought and heat tolerance has not well understood. The objectives of this study were to investigate physiological mechanism of Si on tolerance to drought and heat stress in creeping bentgrass under growth chamber and field conditions. The five treatments from two Si products (Potassium silicate at 0.95 and 1.91 mL m-2, and Ortho-Si at 0.16 and 0.32 mL m-2) were applied biweekly to creeping bentgrass, and treated grass was subjected to heat and drought stress for 56 days and also the treatments were applied to creeping bentgrass putting green in the field conditions. Turfgrass quality, physiological parameters and root growth characteristics were evaluated biweekly. Deficit irrigation was applied to induce drought stress in June and July in the field plots. Foliar application of the Si products improved turf quality, photochemical efficiency, leaf chlorophyll and carotenoid content, antioxidant enzyme activity and endogenous Si content. The Si treatments at the high rates also improved root biomass, length, surface area, volume, and root viability when compared to the control. The results from the field study confirmed the findings in the growth chamber study. The exogenous Si may improve drought and heat tolerance by enhancing root growth and viability, Si uptake by roots, and up-regulation of antioxidant activity, protecting photosynthetic function. The results of this study suggest that foliar application of Si products may be considered as an effective approach to improve turf quality and physiological fitness of creeping bentgrass during the summer months in the U.S. transition zone and other regions with similar climate.

Among numerous abiotic environmental factors, varying light quality and intensity elicit photosynthetic responses that can play vital roles in the optimization of crop production in controlled environment agriculture. Earlier and preliminary studies on photosynthetic activity reported that amber light (595 nm) induces higher photosynthetic rates and quantum yield of plants is a wavelength-dependent response. To resolve the most accurate ePAR curves in cannabis (Cannabis sativa), this study investigated the spectral response of photosynthesis by examining the effects of the leaf versus the whole plant on the impact of photosynthetic activity. A customized CO2 chamber equipped with relative humidity, temperature, and CO2 was used to collect leaf and whole plant photosynthetic data from 5 week old clones with different monochromatic wavelengths (380–750 nm) using the LI-6800 Portable Photosynthesis System (LI-COR) equipped with the Large Leaf and Needle Chamber (LI-COR 6800-13). Differences and correlation between photosynthetic activity at the leaf level and the whole plant were determined. Subsequent studies will involve the combinations of different wavelengths at different ratios. Findings will expand the current understanding of the photosynthetic response of plants to light and provide highly resolved spectral quantum yield curves.

The adoption of supplemental lighting in horticulture has allowed greenhouse growers to increase the yield of multiple crops by at least 10%, with a 300% yield increase documented for cucumbers when transitioning from unlit to lit production. Since then, horticultural lighting has advanced significantly to now include dynamic LED lighting, which provides unparalleled control over the light intensity, spectrum and zoning within the greenhouse. This has allowed greenhouse growers to further maximize crop productivity, but also to target improvements in crop quality and to diversify their production. For example, the greenhouse industry has seen the introduction of multiple berry crops, leafy crops, Asian cucumbers, etc. in recent years, all of which have varying lighting requirements ranging from 12 to 25 mol of light per square meter per day. The ideal spectrum also differs between crops, as do the light saturation points and target intensities. Beyond enhancing photosynthesis and increasing crop productivity, dynamic LED lighting can also be used to improve the nutritional quality and taste of various crops through spectral adjustments during the growth cycle. In a trial comparing the impact of broad and narrow spectra on basil, a broad spectrum produced a flavor profile stronger in eucalyptol whereas a narrow spectrum produced an estragole-dominant crop. This resulted in a milder flavor under a broad spectrum and a stronger flavor under a narrow spectrum. With dynamic lighting, growers can adjust the spectrum to target different flavors and thus different markets. Further, the application of high levels of blue light during the last week of production has been repeatedly shown to enhance the antioxidant capacity of red leafy greens through the bioaccumulation of anthocyanin. The Brix, or sweetness, of fruiting crops has also been improved under dynamic lighting, with commercial trials showing a minimum of 7% increase in Brix in speciality cherry tomatoes compared to fixed spectrum lighting. This increase could potentially be enhanced with end-of-day (EOD) light treatments, which early trials have suggested to enhance the translocation of sugars from leaves to fruit. As such, dynamic LED lighting can improve both the productivity and nutritional quality of greenhouse crops, allowing forward-thinking growers to meet the growing population’s needs in terms of both quality and quantity.