Search Results

A greenhouse study was conducted to quantify the irrigation requirements of two rose (Rosa hybrida L.) cultivars, RADrazz and Belinda’s Dream, which are widely valued for their ease of maintenance in landscapes, grown at four constant volumetric substrate moisture contents (SMCs) of 10%, 20%, 30%, and 40%. In both cultivars, there were no differences in growth and physiological responses between 30% and 40% SMC. In ‘RADrazz’, shoot dry weight (DW) was reduced by 25% and 86%, root DW was reduced by 27% and 71%, and flower number was reduced by 27% and 86% at 20% and 10% SMC, respectively, compared with 30% SMC. Midday leaf water potential (ψ), photosynthesis (P_n), stomatal conductance (g _S), and transpiration (E) were highest at 30% and 40% SMC and they were lowest at 10% SMC. In ‘Belinda’s Dream’, shoot DW was reduced by 30% and 87%, root DW was reduced by 35% and 81%, and flower number was reduced by 42% and 75% at 20% and 10% SMC, respectively, compared with 30% SMC. Midday ψ was least negative at 40% SMC, whereas it was most negative at 10% SMC. There were no significant differences in midday ψ between 20% and 30% SMC. P_n, g _S, and E were highest at 30% and 40% SMC and lowest at 10% SMC. In summary, plants at 30% and 40% SMC maintained the highest shoot and root DW, flower number, midday ψ, P_n, g _S, and E. Water applied at 30% and 20% SMC was reduced by 31% and 70% compared with 40% SMC with excellent performance at 30% SMC and acceptable growth and quality at 20% SMC. The 10% SMC led to significant growth reduction, poor quality, and 25% mortality.

Tatarian dogwood (Cornus alba) is an ornamental shrub with white fruits, creamy-white flowers, and red stems in fall through late winter and is widely used in residential landscape, public parks, and botanical gardens. Two greenhouse experiments were conducted to characterize the survival, morphological, aesthetic, and physiological responses of tatarian dogwood seedlings to salinity and drought stresses. In Expt. 1, tatarian dogwood seedlings grown in three soilless growing substrates (Metro-Mix 360, 560, and 902) were irrigated with a nutrient solution at an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or saline solution (by adding calculated amount of sodium chloride and calcium chloride) at an EC of 5.0 or 10.0 dS·m⁻¹ once per week for 8 weeks. Results showed that substrate did not influence the growth of tatarian dogwood seedling. All plants irrigated with saline solutions at an EC of 10.0 dS·m⁻¹ died, whereas those irrigated with saline solutions at an EC of 5.0 dS·m⁻¹ exhibited severe foliar salt damage with an average visual score of 1.0 (on a scale of 0 to 5, with 0 = dead and 5 = excellent without foliar salt damage). Compared with the control, saline solutions at an EC of 5.0 dS·m⁻¹ reduced plant height and shoot dry weight (DW) by 50.8% and 55.2%, respectively. Relative chlorophyll content [soil plant analysis development (SPAD) reading], chlorophyll fluorescence (F_v/F_m), and net photosynthesis rate (P_n) also decreased when plants were irrigated with saline solutions at an EC of 5.0 and 10.0 dS·m⁻¹. Leaf sodium (Na⁺) concentration of tatarian dogwood seedlings irrigated with saline solutions at an EC of 5.0 and 10.0 dS·m⁻¹ increased 11 and 40 times, respectively, compared with the control, whereas chloride (Cl^-) concentration increased 25 and 33 times, respectively. In Expt. 2, tatarian dogwood seedlings were irrigated at a substrate volumetric water contents (volume of water/volume of substrate, VWC) of 15%, 20%, 25%, 30%, 35%, 40%, or 45% using a sensor-based automated irrigation system for 60 days. Results showed that drought stress decreased plant growth of tatarian dogwood seedlings with a reduction of 71%, 85%, and 87% in plant height, leaf area, and shoot DW, respectively, when VWC decreased from 45% to 15%, but all plants survived at all VWC treatments. Significant reductions of photosynthesis (P_n), stomatal conductance (g _S), transpiration rate (E), and water potential were also found in plants at a VWC of 15%, compared with other VWCs. However, SPAD readings and F_v/F_m of tatarian dogwood seedlings were similar among the VWCs. In conclusion, tatarian dogwood seedlings were sensitive to the salinity levels tested in this study but could survive at all tested substrate volumetric water contents and exhibited resistance to drought conditions.

The goal of this experiment was to evaluate the efficiency of foliar application of dikegulac sodium on increasing the lateral branching of ‘Merritt’s Supreme’ bigleaf hydrangea (Hydrangea macrophylla). Plants were grown in greenhouses at two locations including El Paso, TX and Kosciusko, MS. Two weeks before application of dikegulac sodium, half of plants were hand-pinched leaving two nodes. Foliar spray of dikegulac sodium at 400, 800, or 1600 mg·L⁻¹ was then applied to pinched and unpinched plants. There were two additional control treatments: pinched or unpinched without application of dikegulac sodium. Data were collected at 2 weeks, 6 weeks, 80 days, and 10 months after treatments. Bigleaf hydrangea plants exhibited severe phytotoxicity including interveinal chlorosis or bleaching of new growth at 2 weeks after application of dikegulac sodium with more pronounced symptoms at higher dikegulac sodium concentrations. The severity of phytotoxicity symptoms became less significant at 6 weeks after treatment. The effect of dikegulac sodium on bigleaf hydrangea plant growth, number of branches, and number of flowers depended on both locations and dosages. In El Paso, TX, dikegulac sodium at 800 or 1600 mg·L⁻¹ inhibited bigleaf hydrangea plant growth at 6 weeks and 80 days after treatment, and this effect disappeared at 10 months after treatment. Dikegulac sodium at all tested dosages doubled or tripled the number of branches of pinched or unpinched bigleaf hydrangea, respectively, at 80 days after treatment. At 10 months after treatment, the number of branches and flowers of bigleaf hydrangea plants tended to increase, but was insignificant. In Kosciusko, MS, dikegulac sodium at 1600 mg·L⁻¹ reduced the plant growth at 6 weeks after treatment. This treatment increased the number of branches and flowers of unpinched plants by 196% and 95% and pinched plants by 53% and 31%, respectively, at 10 months after treatment. Dikegulac sodium application could be used to increase number of branches and flowers and produce compact ‘Merritt’s Supreme’ bigleaf hydrangea. However, the efficacy varied with environmental conditions.

The effects of temperature on flower size and number of flower buds of Campanula carpatica Jacq. 'Blue Clips', 'Deep Blue Clips', and Campanula 'Birch Hybrid' were investigated in four temperature and light-transfer experiments. In year 1, 'Blue Clips' and 'Birch Hybrid' plants were grown initially at 20 °C and then transferred at visible flower bud (VB) to 14, 17, 20, 23, or 26 °C until flower (Expt. 1). In Expt. 2, 'Blue Clips' and 'Birch Hybrid' plants were transferred from 14 to 26 °C or from 26 to 14 °C at various intervals after flower induction. Flower size of both species was negatively correlated with average daily temperature (ADT) after VB; flowers on plants grown at 14 °C were 35% larger than those on plants grown at 26 °C. In contrast, temperature before VB had only a small effect on final flower size in both species, although flower diameter of 'Birch Hybrid' plants grown at constant 26 °C was 20% smaller than that of the plants grown initially at 20°C and then transferred to VB to 26 °C. For both species, the longer the exposure to high temperature after VB, the smaller the flowers. Number of flower buds at flower in 'Birch Hybrid' decreased as ADT after VB increased. In year 2, 'Deep Blue Clips' plants were grown at constant 20 °C under high or low daily light integral (DLI, 17 or 5.7 mol·m^-2·d^-1) until VB, and then transferred to 14, 17, 20, 23, or 26 °C under high or low DLI (Expt. 3). In Expt. 4, 'Deep Blue Clips' plants were grown at 14, 17, 20, 23, or 26 °C until VB, and then transferred to constant 20 °C under high or low DLI until flower. Flower size (petal length) was negatively correlated with ADT both before and after VB, while flower bud number was negatively correlated with the ADT only after VB, regardless of DLI. In both experiments, petal length decreased by 0.3 to 0.5 mm per 1 °C increase in ADT before or after VB. Flowers were larger and more numerous under high than under low DLIs after VB, regardless of the DLI before VB.

The effect of drought on the growth and gas exchange of six bedding plant species—agastache [Agastache urticifolia (Benth.) O. Kuntze `Honeybee Blue'], dusty miller (Cineraria maritima L. `Silverdusty'), petunia (Petunia ×hybrida `Wave Purple'), plumbago (Plumbago auriculata Lam. `Escapade'), ornamental pepper (Capsicum annuum L. `Black Pearl'), and vinca [Catharanthus roseus (L.) G. Don `Titan']—was quantified under greenhouse conditions. Seeds were sown in January and seedlings were grown in the greenhouse until 18 Apr., when two irrigation treatments—drought (D, ≈18% volumetric moisture content at reirrigation) and control (C, ≈25% volumetric moisture content at reirrigation)—were initiated. Leaf net photosynthetic rate (P_n), stomatal conductance (g_s), and transpiration (E) were determined in response to a range of substrate moisture content (from ≈5% to 30% by volume) and temperature (from 20 °C to 40 °C). Dry weight of agastache, ornamental pepper, and vinca was unaffected by drought, whereas that of other species was reduced. Leaf area of plumbago and height of plumbago and vinca were reduced by drought. As substrate moisture content decreased from 25% to 10%, P_n, E, and g_s decreased linearly in all species except petunia and plumbago. Leaf net photosynthetic rate of all species declined as leaf temperature increased from 20 °C to 40 °C. In contrast, E of all species, except petunia, increased as temperature increased. Transpiration rate of petunia increased as temperature increased from 20 °C to 30 °C, and then decreased between 30 °C and 40 °C. Although petunia had the highest P_n among the tested species, its P_n and g_s declined more rapidly compared with the other species as temperature increased from 20 °C to 40 °C or as substrate moisture content decreased, indicating that petunia was most sensitive to high temperature and drought.

Ornamental chile peppers are popular bedding plants. As high-quality water supply becomes limited in many parts of the world, alternative waters such as municipal reclaimed water is encouraged to be used for landscape irrigation. The purpose of this study was to assess the relative salt tolerance of 10 cultivars of ornamental chile peppers by irrigating the mature plants with saline solutions and germinating seeds in saline substrate in a greenhouse. In the mature plant salt tolerance experiment, plants were irrigated with nutrient solution (no addition of salts, control) or saline solution at electrical conductance (EC) of 4.1 dS·m⁻¹ or 8.1 dS·m⁻¹ for 8 weeks. Plants in the EC of 4.1 dS·m⁻¹ treatment did not have any foliar salt damage regardless of cultivar. At EC of 8.1 dS·m⁻¹, ‘NuMex Memorial Day’ had the most severe foliar salt damage, whereas ‘NuMex April Fool’s Day’, ‘NuMex Cinco de Mayo’, ‘NuMex Thanksgiving’, and ‘NuMex Twilight’ had little or no foliar damage. Shoot dry weight (DW) reduction at EC of 8.1 dS·m⁻¹ compared with control was smallest in ‘NuMex Thanksgiving’ (15%), whereas ‘NuMex Memorial Day’ had the greatest reduction of 74% followed by ‘NuMex Christmas’ of 61%. The highest shoot DW reduction in ‘NuMex Memorial Day’ coincided with lowest visual score, indicating that this cultivar was the least tolerant to salinity. The leaf Na⁺ and Cl⁻ concentrations increased dramatically with increasing EC of the irrigation water in all cultivars. The highest Na⁺ concentration of 10.9 mg·g⁻¹ DW at EC of 8.1 dS·m⁻¹ was observed in ‘NuMex Christmas’. The highest Cl⁻ concentration at EC of 8.1 dS·m⁻¹ was found in ‘NuMex Memorial Day’ with 64.8 mg·g⁻¹ DW, which was four times higher than the control. In the seedling emergence experiment, seeds of the 10 cultivars were germinated in substrate either moistened with reverse osmosis water (EC ≈0) or saline solution at EC of 17.1 dS·m⁻¹. ‘NuMex Christmas’ and ‘NuMex Memorial Day’ had the lowest relative seedling emergence index, indicating that these two cultivars were the least tolerant to salinity during the seedling emergence stage. ‘NuMex Thanksgiving’ and ‘NuMex Cinco de Mayo’ had the highest relative seedling emergence index. Combining the results from both experiments, we concluded that ‘NuMex Cinco de Mayo’ and ‘NuMex Thanksgiving’ were the most tolerant cultivars, whereas ‘NuMex Christmas’ and ‘NuMex Memorial Day’ were the least tolerant ones.

A greenhouse study was conducted to evaluate the response of four garden roses (Rosa ×hybrid L.), ‘RADrazz’, ‘Belinda’s Dream’, ‘Old Blush’, and ‘Marie Pavie’, to drought stress. Plants grown in containers were subjected to two watering treatments, well-irrigated [water as needed: ≈35% substrate moisture content (SMC) at re-watering] and cyclic drought stress (withholding irrigation until plants exhibit incipient wilting: ≈10% SMC, then re-watering to field capacity for subsequent dry down). Shoot growth and flower number were reduced in the drought treatment compared with the well-irrigated plants in all cultivars with least reduction in ‘RADrazz’. Drought stress reduced root growth in ‘Belinda’s Dream’ and ‘Marie Pavie’, whereas there was no difference in root growth in ‘RADrazz’ and ‘Old Blush’. Decreased SMC induced reduction in net photosynthetic rate (P_n), stomatal conductance (g _S), transpiration rate (E), and midday leaf water potential (ψ). Leaf water use efficiency (WUE) increased as SMC decreased in all cultivars. However, the relationship between these physiological parameters and SMC differed among the cultivars. At SMC between 10% and 20%, ‘RADrazz’ had higher P_n, g _S, E, and WUE compared with the other three cultivars. Therefore, ‘RADrazz’ was the most drought-tolerant during container production among the cultivars investigated. With lower gas exchange rates and greater reduction in flower number at low SMC, ‘Marie Pavie’ was less drought-tolerant compared with the other three cultivars.

High concentration of aluminum ion (Al³⁺) in acidic soil often negatively affects plant growth. To deepen understanding of the mechanisms of physiological response to Aluminum (Al) toxicity, changes in physiology and cell ultrastructure of oil tea (Camellia oleifera) were investigated under different Al levels. Oil tea plants were grown in pots filled with sand and treated with Al at 0, 0.5, 1.25, 2.0, or 4.0 mm. Results showed that Al at 0.5–2.0 mm improved plant growth, whereas Al at 4.0 mm inhibited root growth and damaged cell ultrastructure. Net photosynthetic rate (P_n), stomatal conductance (g _s), transpiration rate (T_r), and photochemical efficiency increased as Al concentration increased from 0 to 2.0 mm; however, all parameters mentioned previously decreased at 4.0 mm. The activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in leaves treated with 2.0 mm Al reached the maximum, which were 29%, 63%, and 28% higher than that of control. When Al was ≤2.0 mm, the content of soluble sugar and soluble protein increased with increasing Al concentration. These results may indicate that oil tea adapted to Al stress through osmotic adjustment and through increasing antioxidant enzyme system. In summary, Al at low concentration (0.5–2.0 mm) improved growth and physiological performance, whereas 4.0 mm negatively impacted performance of oil tea.

Asteraceae is one of the largest plant families with many important garden ornamental species. Salt tolerance of 10 aster perennials was evaluated in a greenhouse experiment, including the following: damianita (Chrysactinia mexicana), gregg’s mistflower (Eupatorium greggii), shasta daisy (Leucanthemum ×superbum ‘Becky’), blackfoot daisy (Melampodium leucanthum), lavender cotton (Santolina chamaecyparissus), aromatic aster (Symphyotrichum oblongifolium), copper canyon daisy (Tagetes lemmonii), four-nerve daisy (Tetraneuris scaposa), skeleton-leaf goldeneye (Viguiera stenoloba), and zexmenia (Wedelia texana). Plants were irrigated with nutrient solution at electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or saline solutions at EC of 5.0 or 10.0 dS·m⁻¹ (EC 5 or EC 10) for 5 weeks. Upon termination, growth parameters, foliar salt damage, relative chlorophyll content [Soil-Plant Analysis Development (SPAD) readings], and mineral concentration were measured. Gregg’s mistflower, skeleton-leaf goldeneye, and lavender cotton were the most salt-tolerant species with less reductions in shoot dry weight (DW) in both EC 5 and EC 10. Considering the relatively severe foliar salt damage (visual quality score of 3.1 and 2.7 at EC 5; 2.4 and 1.6 at EC 10) and mortality rate (10% and 40%) in EC 10, aromatic aster and zexmenia should be avoided where poor quality water may be used for irrigation. Gregg’s mistflower and skeleton-leaf goldeneye had relatively lower leaf sodium (Na) concentrations suggesting that both species can selectively exclude Na. Damianita and the four daisies, i.e., blackfoot daisy, copper canyon daisy, four-nerve daisy, and shasta daisy, were salt sensitive as evidenced by their greater growth reduction, foliar salt damage, and high Na and chlorine (Cl) accumulation in leaves, and should be avoided in landscapes where poor quality water may be used for irrigation.

Market researchers have found that nursery and greenhouse production practices that reduce plastic use can increase consumer interest. However, there are broader crop performance, production efficiency, and environmental factors that must be considered before adopting containers made with alternative materials. This review highlights current commercially available alternative containers and parent materials. In addition, findings from recent and ongoing nursery, greenhouse, and landscape trials are synthesized, identifying common themes, inconsistencies, research gaps, and future research needs.