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Lifei Chen, Youping Sun, Genhua Niu, Qiang Liu, and James Altland

Relative salt tolerance of eight Berberis thunbergii (japanese barberry) cultivars (B. thunbergii ‘Celeste’, ‘Kasia’, ‘Maria’, ‘Mini’, and ‘Talago’; B. thunbergii var. atropurpurea ‘Concorde’, ‘Helmond Pillar’, and ‘Rose Glow’) was evaluated in a greenhouse experiment. Plants were irrigated with nutrient solution at an electrical conductivity (EC) of 1.2 dS·m−1 (control) or saline solutions at an EC of 5.0 or 10.0 dS·m−1 (EC 5 or EC 10) once a week for 8 weeks. At 4 weeks after treatment, all barberry cultivars in EC 5 had minimal foliar damage with visual scores of 4 or greater (visual score 0: dead, 5: excellent). At 8 weeks after treatment, in EC 5, ‘Helmond Pillar’, ‘Maria’, ‘Mini’, and ‘Rose Glow’ plants exhibited slight foliar salt damage with an average visual score of 3.5, whereas ‘Celeste’, ‘Concorde’, ‘Kasia’, and ‘Talago’ had minimal foliar salt damage with an averaged visual score of 4.4. However, most barberry plants in EC 10 exhibited severe foliar salt damage 4 weeks after treatment with the exception of ‘Concorde’ and were dead 8 weeks after treatment. Compared with control, at the end of the experiment (8 weeks of treatments), shoot dry weight (DW) of ‘Celeste’, ‘Helmond Pillar’, ‘Maria’, and ‘Rose Glow’ in EC 5 was reduced by 47%, 47%, 50%, and 42%, respectively, whereas shoot DW of ‘Concorde’, ‘Kasia’, ‘Mini’, and ‘Talago’ in EC 5 did not change. In EC 10, shoot DW of ‘Celeste’, ‘Concorde’, ‘Kasia’, and ‘Talago’ was reduced by 75%, 35%, 55%, and 46%, respectively. The averaged sodium (Na) concentration of all barberry cultivars in EC 5 and EC 10 was 34 and 87 times, respectively, higher than the control, whereas leaf chloride (Cl) concentration of all barberry cultivars in EC 5 and EC 10 was 14–60 and 29–106 times, respectively, higher than the control. Growth, visual quality, and performance index (PI) were all negatively correlated with leaf Na and Cl content in all cultivars, suggesting that excessive Na and Cl accumulation in the leaf tissue led to growth reduction, salt damage, and death. In summary, ‘Concorde’, ‘Kasia’, and ‘Talago’ were relatively salt tolerant; ‘Helmond Pillar’, ‘Maria’, ‘Mini’, and ‘Rose Glow’ were relatively salt sensitive; and ‘Celeste’ was in between the two groups. Generally, barberry plants had moderate salt tolerance and can be irrigated with marginal water at an EC of 5 dS·m−1 or lower with slight foliar damage.

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Liyuan Huang, Jun Yuan, Hui Wang, Xiaofeng Tan, and Genhua Niu

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 (Pn), stomatal conductance (g s), transpiration rate (Tr), 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.

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Genhua Niu, Denise S. Rodriguez, Lizzie Aguiniga, and Wayne Mackay

Use of recycled water to irrigate urban landscapes and nursery plants may be inevitable as fresh water supplies diminish and populations continue to grow in the arid and semiarid southwestern United States. Lupinus havardii Wats. (Big Bend bluebonnet) has potential as a cut flower and Lupinus texensis Hook. (Texas bluebonnet) as a bedding plant, but little information is available on salt tolerance of these species. A greenhouse study was conducted to characterize the growth in response to various salinity levels. Plants were grown in 10-L containers and drip-irrigated with synthesized saline solutions at electrical conductivity levels of 1.6, 3.7, 5.7, 7.6, or 9.4 dS·m−1. Although shoot growth of L. texensis was reduced as salinity levels increased, it was visually acceptable (without any visual injury) when irrigated with salinity levels of less than 7.6 dS·m−1. All plants survived at 7.6 dS·m−1, whereas only 15% did at 9.4 dS·m−1. In contrast, L. havardii had leaf injury at 5.7 dS·m−1. No plants survived at 9.4 dS·m−1, and only 7% plants survived at 7.6 dS·m−1. In addition, growth of L. havardii was significantly reduced and plants were shorter at elevated salinity levels. Cut raceme yield of L. havardii decreased at salinity levels greater than 3.7 dS·m−1. However, no difference in cut raceme yield was observed between the control and 3.7 dS·m−1, although shoot growth was reduced. Overall, L. texensis was more salt-tolerant than L. havardii.

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Genhua Niu, Denise S. Rodriguez, and Yin-Tung Wang

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 (Pn), stomatal conductance (gs), 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%, Pn, E, and gs 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 Pn among the tested species, its Pn and gs 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.

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Genhua Niu, Pedro Osuna, Youping Sun, and Denise S. Rodriguez

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.

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Ockert Greyvenstein, Brent Pemberton, Terri Starman, Genhua Niu, and David Byrne

The decline in sales of garden roses can, in part, be attributed to the lack of well-adapted cultivars. Successful selection for any trait requires an accurate phenotyping protocol. Apart from field screening, a protocol for phenotyping high-temperature tolerance in garden roses is yet to be established. An experiment was conducted to determine the stage of development when flowers were most sensitive to high-temperature stress. Liners of Rosa L. ‘Belinda’s Dream (BD) and the Knock Out® rose ‘RADrazz’ (KO) were planted in a soilless medium and grown in a greenhouse. Established plants were pruned retaining several nodes with leaves on two main shoots and treatments started. The experiment was conducted in growth chambers held at either 24/17 °C (control) or 36/28 °C (stress) day/night temperatures. Six time and duration temperature treatments included 8 weeks of continuous control conditions, 8 weeks of continuous stress conditions, and four sequential 2-week high-temperature shock treatments. Continuously stressed plants flowered in the least amount of days but did not differ from the continuous control-treated plants based on nonlinear thermal unit accumulation until flowering. Both cultivars had a 70% reduction in flower dry weight under continuous stress conditions. Flowers were most sensitive to high-temperature stress at the visible bud stage, which corresponds to Weeks 5 to 6 and Weeks 7 to 8 for BD and Weeks 3 to 4 and Weeks 5 to 6 for KO, respectively. KO was more resistant to flower abscission than BD when treated at the visible bud stage, but no difference in flower dry weight reduction between BD and KO was found. The number of vegetative nodes to the flower was unaffected by treatment and differed between the cultivars.

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Xiaoya Cai, Terri Starman, Genhua Niu, and Charles Hall

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 (Pn), 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. Pn, 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, Pn, 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.

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Xiaoya Cai, Youping Sun, Terri Starman, Charles Hall, and Genhua Niu

Earth-Kind® is a special designation given to select rose cultivars with superior stress tolerance (heat, drought, and pest tolerance) and outstanding landscape performance. The responses of Earth-Kind® roses to high salinity stress are unknown. A greenhouse study was conducted to evaluate 18 Earth-Kind® rose cultivars (Belinda’s Dream, Cecile Brunner, Climbing Pinkie, Ducher, Duchesse de Brabant, Else Poulsen, Georgetown Tea, La Marne, Madame Antoine Mari, Marie Daly, Monsieur Tillier, Mrs. Dudley Cross, Mutabilis, Perle d’Or, Reve d’Or, Sea Foam, Souvenir de St. Anne’s, and Spice) in College Station and 10 of the same 18 cultivars in El Paso in response to two salinity levels at electrical conductivity (EC) of 1.2 (control, nutrient solution) and 10.0 dS·m−1 (EC 10). In both locations, ‘Belinda’s Dream’ and ‘Climbing Pinkie’ in EC 10 had no or little reduction in shoot growth, flower number, and leaf SPAD readings. The net photosynthetic rate (Pn), stomatal conductance (g S), and transpiration (E) did not decrease in these two cultivars at EC 10 in El Paso. In College Station, ‘Mrs. Dudley Cross’, ‘Reve d’Or’, and ‘Sea Foam’ in EC 10 also had no or little reduction in shoot growth, flower number, and leaf SPAD readings. In both locations, ‘Cecile Brunner’ and ‘Else Poulsen’ in EC 10 had severe visual foliar salt damage, and they had the greatest reductions in shoot growth and flower number. In addition to these two cultivars, the lowest relative shoot dry weight (DW) and flower number was observed in ‘Madame Antoine Mari’, ‘Perle d’Or’, ‘Spice’, and ‘Souvenir de St. Anne’s’ in College Station. In summary, ‘Belinda’s Dream’, ‘Climbing Pinkie’, ‘ Mrs. Dudley Cross’, ‘Reve d’Or’, and ‘Sea Foam’ were the most salt-tolerant cultivars, whereas ‘Cecile Brunner’, ‘Else Poulsen’, ‘Madame Antoine Mari’, ‘Perle d’Or’, ‘Spice’, and ‘Souvenir de St. Anne’s’ were the least salt-tolerant among the cultivars investigated.

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Genhua Niu, Royal Heins, Arthur Cameron, and William Carlson

The influence of vernalization temperature and duration and devernalization treatments on subsequent growth and flower development of Campanula `Birch Hybrid' and Leucanthemum ×superbum Bergman ex J. Ingram `Snow Cap' was determined. In the vernalization experiment, plants of `Birch Hybrid' were vernalized at 0, 2.5, 5, 7.5, or 10 °C for 2, 4, 6, or 8 weeks. `Snow Cap' was vernalized at 0, 2.5, 5, or 10 °C for 2, 4, 6, or 8 weeks. In another devernalization experiment, plants of both species were moved to a high temperature (30/10 °C, day/night) growth chamber for 2 or 4 days at various times during or after the 6-week vernalization period. A 6-week vernalization was necessary to obtain 100% flowering in `Birch Hybrid', and 8 weeks of vernalization decreased time to flower by 7 to 10 days compared with 6-week vernalization. Exposure to high temperature for 2 days during or immediately after vernalization did not devernalize `Birch Hybrid' plants, while a 4-day exposure decreased flowering percentage in some treatments and delayed flowering by 7 to 10 days. There were no significant differences in flowering characteristics of `Snow Cap' plants vernalized at 0 to 5 °C for 4 to 8 weeks. A 2-week vernalization at 0, 2.5, 5, or 10 °C or 4 to 8 week vernalization at 10 °C delayed flowering by 5 to 10 days compared with those vernalized at 0 to 5 °C for 4 to 8 weeks. Exposure to high temperature for 2 d did not devernalize `Snow Cap' plants regardless of exposure times, but a 4-day exposure delayed flowering by 4 to 5 days in some treatments. Combined, the data indicate that `Birch Hybrid' has an obligate 6-week vernalization requirement and `Snow Cap' has a facultative 4-week vernalization requirement that can be fulfilled in the 0 to 10 °C range. Exposure to temperatures of 30 °C (9 h·d-1) for 12 out of 42 days did not devernalize either species but in some cases caused a small delay in time to flower.

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Genhua Niu, Royal D. Heins, Arthur Cameron, and Will Carlson

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.