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.
Liyuan Huang, Jun Yuan, Hui Wang, Xiaofeng Tan, and Genhua Niu
Genhua Niu, Minzi Wang, Denise Rodriguez, and Donglin Zhang
As high-quality water supply becomes limited in many regions of the world, alternative water sources are being used for irrigating urban landscapes. Therefore, salt-tolerant landscape plants are needed. Two greenhouse experiments were conducted to screen the salt tolerance of Zinnia marylandica (‘Zahara Coral Rose’, ‘Zahara Fire’, ‘Zahara Scarlet’, ‘Zahara Starlight’, ‘Zahara White’, and ‘Zahara Yellow’) and Z. maritima ‘Solcito’. In Expt. 1, plants were subirrigated with nutrient or saline solutions at electrical conductivity (EC) at 1.4 (base nutrient solution, control), 3.0, 4.2, 6.0, or 8.2 dS·m−1 for 4 weeks, whereas in Expt. 2, plants were surface-irrigated with the same nutrient or saline solutions for 4 weeks. In Expt. 1, all plants, regardless of cultivar, died by the end of the treatment at EC 6.0 and EC 8.2 as a result of high salinity in the root zone. Plants became shorter and more compact as EC of irrigation water increased. Shoot dry weight of all cultivars in EC 4.2 was reduced by 50% to 56% compared with that of the control. Shoot Na+ and Cl– accumulated excessively as salinity increased in the irrigation water, whereas Ca2+, Mg2+, and K+ did not change substantially. In Expt. 2, mortality varied with cultivar and treatment. Similar to Expt. 1, growth reduction resulting from elevated salinity across cultivars was found. Therefore, it is concluded that zinnia cultivars used in this study are sensitive to salinity and should not be planted in areas with high soil salinity or when alternative waters with high salinity may be used for irrigation.
Jun Yuan, Liyuan Huang, Naifu Zhou, Hui Wang, and Genhua Niu
Aluminum (Al) toxicity and phosphorus (P) deficiency are two crucial factors limiting the production of Camellia oleifera, which is grown commercially in red acidic soils in Southern China. The current study characterized the different forms of P and Al in the red acidic soils of C. oleifera plantations. Soil and plant tissue samples taken from 32 Camellia plantations across Hunan province were analyzed. Furthermore, a pot experiment with nutrient solutions of different Al and P contents was carried out to investigate P and Al uptake and their effect on C. oleifera growth. The results showed that the P content extracted by NaOH (Fe-P) was the highest in all types of soil samples (rhizosphere, 0–20 cm, and 20–40 cm zones), followed by P extracted by NH4F (Al-P), H2SO4 (Ca-P), and Na3C6H5O7 (O-P). HCl (In-Al), NH4Ac (Ha-Al), and Na4P2O7·10H2O (Or-Al) extracted Al were the main forms and accounted for 22.8%, 23.1%, and 23.8% of total Al, respectively. KCl extracted Al (Ex-Al) contents in the rhizosphere, 0–20 cm, and 20–40 cm soil zones were 4.78, 4.86, and 4.59 mg·kg−1, respectively. P contents in roots, young leaves, and old leaves were 0.80, 0.82, and 0.64 mg·kg−1, respectively. The highest Al content of 11.35 g·kg−1 was found in the old leaves, followed by roots and young leaves. Correlation analyses revealed that P in roots was positively associated with available P (AP) and Al-P in rhizosphere. P in roots and young leaves also had a positive correlation with Ex-Al, whereas Al in old leaves was positively correlated with In-Al and total Al. Significant correlations between Al-P, Ex-Al, and AP were detected. The pot experiment indicated that adding Al or P alone increased plant growth and Al or P uptake, respectively. When adding both Al and P, significant synergistic effect was found. These results suggest that Al is beneficial to C. oleifera, which may be the adaptive mechanism of C. oleifera to use insoluble Al-P in red acidic soil.
Triston Hooks, Genhua Niu, Joe Masabni, Youping Sun, and Girisha Ganjegunte
Pomegranate is a drought-tolerant and salt-tolerant crop. Its fruits contain high levels of phytochemicals that have many health benefits. Pomegranate has the potential to be an alternative crop in areas where water availability is limited, such as west Texas. However, more than 500 pomegranate varieties are estimated to exist worldwide, and little is known about which varieties are suitable for growing in the west Texas region. Therefore, the objective of this study was to evaluate the field performance of 22 pomegranate varieties, specifically based on phenology, resistance to sunburn, fruit split, fruit rot (resistance was calculated by subtracting the percent incidence by 100), yield, fruit phytochemicals, and Brix over the course of 3 years from 2016 to 2018. Cold damage, caused by below-freezing temperatures encountered from Nov. 2018 to Feb. 2019, was also evaluated in Apr. 2019. Our results showed significant varietal differences in nearly all response variables measured, indicating that varietal selection is important for pomegranate production for specific regions, such as west Texas. Leaf budding ranged from 47 to 62 days in 2016, 41 to 54 days in 2017, and 49 to 60 days in 2018. Anthesis ranged from 87 to 119 days in 2016, 80 to 94 days in 2017, and 92 to 114 days in 2018. Fruit resistance to split was broad and ranged from 7.3% to 79.1% in 2017 and from 14.2% to 99.7% in 2018. Fruit sunburn resistance ranged from 14.0% to 64.6% in 2017 and from 28.3% to 90.0% in 2018. Fruit heart rot incidence was nominal for all varieties. Total phenolic compound contents of the pomegranate fruit juice ranged from 0.81 to 1.52 mg GAE/mL, and the total antioxidant capacity ranged from 3.44 to 6.81 mg TE/mL. The yield per tree ranged from 1.00 to 7.96 kg in 2017 and from 0.81 to 10.26 kg in 2018. Brix ranged from 12.5% to 17.4% in 2017 and from 13.9% to 18.4% in 2018. Early winter below-freezing temperatures caused different degrees of cold damage; however, 5 of 22 varieties that originated from Russia did not show any cold damage. Results of a hierarchical cluster analysis based on the means of the key response variables of yield and Brix indicated that four varieties (Al-Sirin-Nar, Russian 8, Ben Ivey, and Salavatski) were notable for having both high yield and high Brix.
Haijie Dou, Genhua Niu, Mengmeng Gu, and Joseph G. Masabni
Consumption of basil (Ocimum basilicum) has been increasing worldwide in recent years because of its unique aromatic flavor and relatively high concentration of phenolics. To achieve a stable and reliable supply of basil, more growers are turning to indoor controlled-environment production with artificial lighting due to its high environmental controllability and sustainability. However, electricity cost for lighting is a major limiting factor to the commercial application of indoor vertical farming, and little information is available on the minimum light requirement to produce uniform and high-quality sweet basil. To determine the optimal daily light integral (DLI) for sweet basil production in indoor vertical farming, this study investigated the effects of five DLIs, namely, 9.3, 11.5, 12.9, 16.5, and 17.8 mol·m−2·d−1 on basil growth and quality. ‘Improved Genovese Compact’ sweet basil was treated with five DLIs provided by white fluorescent lamps (FLs) for 21 d after germination, and gas exchange rate, growth, yield, and nutritional quality of basil plants were measured to evaluate the effects of the different DLIs on basil growth and quality. Results indicated that basil plants grown under higher DLIs of 12.9, 16.5, or 17.8 mol·m−2·d−1 had higher net photosynthesis, transpiration, and stomatal conductance (g S), compared with those under lower DLIs of 9.3 and 11.5 mol·m−2·d−1. High DLIs resulted in lower chlorophyll (Chl) a+b concentration per leaf fresh weight (FW), higher Chl a/b ratios, and larger and thicker leaves of basil plants. The shoot FW under DLIs of 12.9, 16.5, and 17.8 mol·m−2·d−1 was 54.2%, 78.6%, and 77.9%, respectively, higher than that at a DLI of 9.3 mol·m−2·d−1. In addition, higher DLIs led to higher soluble sugar percent and dry matter percent than lower DLIs. The amounts of total anthocyanin, phenolics, and flavonoids per plant of sweet basil were also positively correlated to DLIs, and antioxidant capacity at a DLI of 17.8 mol·m−2·d−1 was 73% higher than that at a DLI of 9.3 mol·m−2·d−1. Combining the results of growth, yield, and nutritional quality of sweet basil, we suggest a DLI of 12.9 mol·m−2·d−1 for sweet basil commercial production in indoor vertical farming to minimize the energy cost while maintaining a high yield and nutritional quality.
Zhengnan Yan, Dongxian He, Genhua Niu, Qing Zhou, and Yinghua Qu
Few researchers examined different red light amounts added in white light-emitting diodes (LEDs) with varied daily light integrals (DLIs) for hydroponic lettuce (Lactuca sativa L.). In this study, effects of DLI and LED light quality (LQ) on growth, nutritional quality, and energy use efficiency of hydroponic lettuce were investigated in a plant factory with artificial lighting (PFAL). Hydroponic lettuce plants (cv. Ziwei) were grown for 20 days under 20 combinations of five levels of DLIs at 5.04, 7.56, 10.08, 12.60, and 15.12 mol·m−2·d−1 and four LQs: two kinds of white LEDs with red to blue ratio (R:B ratio) of 0.9 and 1.8, and two white LEDs plus red chips with R:B ratio of 2.7 and 3.6, respectively. Results showed that leaf and root weights and power consumption based on fresh and dry weights increased linearly with increasing DLI, and light and electrical energy use efficiency (LUE and EUE) decreased linearly as DLI increased. However, no statistically significant differences were found in leaf fresh and dry weights and nitrate and vitamin C contents between DLI at 12.60 and 15.12 mol·m−2·d−1. Also, no effects of LQ on leaf dry weight of hydroponic lettuce were observed at a DLI of 5.04 mol·m−2·d−1. White plus red LEDs with an R:B ratio of 2.7 resulted in higher leaf fresh weight than the two white LEDs. LUE increased by more than 20% when red light fraction increased from 24.2% to 48.6%. In summary, white plus red LEDs with an R:B ratio of 2.7 at DLI at 12.60 mol·m−2·d−1 were recommended for commercial hydroponic lettuce (cv. Ziwei) production in PFALs.
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.
Xiaoya Cai, Terri Starman, Genhua Niu, Charles Hall, and Leonardo Lombardini
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 (Pn), 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 Pn, 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.
Youping Sun, Genhua Niu, Haijie Dou, Christina Perez, and Lisa Alexander
Hydrangeas are popular landscape plants that are widely grown in many parts of the world. The objective of this study was to evaluate the salinity tolerance of three novel Dichroa ×hydrangea hybrids [Dichroa febrifuga ‘Yamaguchi Hardy’ × Hydrangea macrophylla ‘Hamburg’ (YH × Hamburg), Dichroa febrifuga ‘Yellow Wings’ ×Hydrangea macrophylla ‘Nigra’ (YW × Nigra), and Dichroa febrifuga ‘Yellow Wings’ ×Hydrangea macrophylla ‘Oakhill’ (YW × Oakhill)]. A 52-day greenhouse study was conducted by irrigating container-grown plants with nutrient solution at an electrical conductivity (EC) of 1.1 dS·m−1 (control) or saline solution at an EC of 5.0 dS·m−1 (EC 5) or 10.0 dS·m−1 (EC 10). At harvest, YH × Hamburg and YW × Nigra in EC 5 and EC 10 still exhibited good quality with average visual scores greater than 4.1 (0 = dead; 5 = excellent). For YW × Oakhill, moderate foliar salt damage was observed with an average visual score of 2.9 in EC 5 and 2.2 in EC 10. Compared with control, the shoot dry weight of YH × Hamburg, YW × Nigra, and YW × Oakhill in EC 5 reduced by 35%, 35%, and 55%, respectively, whereas that in EC 10 decreased by 58%, 58%, and 67%, respectively. Elevated salinity also decreased plant height, leaf area, and leaf greenness [Soil Plant Analysis Development (SPAD) readings]; chlorophyll fluorescence (Fv/Fm); performance index (PI); and net photosynthetic rate (Pn). All these responses might result from excess accumulation of sodium (Na+) and chloride (Cl−) ions in hydrangea leaves. In this study, compared with control, leaf Na+ concentration of YH × Hamburg, YW × Nigra, and YW × Oakhill increased 11, 36, and 14 times, respectively, in EC 5, and 31, 53, and 18 times, respectively, in EC 10. Compared with control, leaf Cl− concentration increased 4, 9, and 7 times in EC 5, and 10, 11, and 8 times in EC 10 for YH × Hamburg, YW × Nigra, and YW × Oakhill, respectively. Leaf nitrogen (N), phosphorous (P), potassium (K+), and iron (Fe3+) concentrations decreased at elevated salinity levels but did not cause any nutrient deficiency. In summary, the three Dichroa ×hydrangea hybrids exhibited different salinity tolerance: YH × Hamburg and YW × Nigra were more tolerant than YW × Oakhill. Salt-tolerant hydrangea hybrids should be chosen for landscape use if soil and/or irrigation water are salty.
Joseph Masabni, Youping Sun, Genhua Niu, and Priscilla Del Valle
Southern U.S. states such as Texas experience high temperatures and intense solar radiation during the summer production season. Use of shadecloth is common in Spain and other Mediterranean countries and is becoming popular with homeowners or small-acreage farmers in Texas. Little information is available on the applicability of using shadecloth on tomato (Solanum lycopersicum) and chili pepper (Capsicum annuum) in the warm climate of Texas. The effects of two shade nets differing in shading intensity on growth, chlorophyll fluorescence, and photosynthesis of ‘Celebrity’ tomato and ‘Sweet Banana’ chili pepper was investigated from May to Aug. 2014. Plants were grown in 50% shade, 70% shade, or full sun. Compared with the unshaded control, tomato grown in 50% shade had similar yield and shoot fresh and dry weight and less photochemical stress. The 50% shade reduced number and weight of unmarketable tomato fruit. Similar results were obtained with chili pepper except for lower numbers of marketable fruit. The 70% shade significantly reduced yield parameters of both tomato and chili pepper. Both 50% and 70% shadecloth reduced leaf temperatures of tomato and chili pepper with variable results in June and July. Growth index [(height + width 1 + width 2) ÷ 3] of tomato and chili pepper was the highest with 50% shade, the lowest with full sun, and intermediate with 70% shade. The maximum net photosynthetic rates (Pn) of tomato determined from a Pn to light response curve supported the results on growth and yield. However, the maximum Pn of chili pepper was higher in full sun treatment compared with 50% or 70% shade. The latter two were almost identical. This one growing season study indicated that shading at 50% benefits tomato and chili pepper production in west Texas by reducing heat stress; however, a shading percentage below 50% may be better.