Seed Priming Enhances Seed Germination and Morphological Traits of Lactuca sativa L. under Salt Stress

Seed germination is the stage in which plants are most sensitive to abiotic stress, including salt stress (SS). SS affects plant growth and performance through ion toxicity, decreasing seed germination percentage and increasing the germination time. Several priming treatments were used to enhance germination under SS. The objectives of this study were (1) to identify priming treatments to shorten the emergence period, (2) to evaluate priming treatments against the SS, and (3) to induce synchronized seed germination. Salt-sensitive ‘Burpee Bibb’ lettuce seeds were treated with 0.05% potassium nitrate, 3 mM gibberellic acid, and distilled water. All the primed and non-primed seeds were subjected to 100 mM sodium chloride (NaCl) or 0 mM NaCl (control). The seven-day experiment, arranged in a complete randomized block design with four replications, was conducted in a growth chamber maintained with 16/8 h photoperiod (light/dark), 60% relative humidity, and a day/night temperature of 22/18 °C. The result indicated that hydro-primed (HP) seeds were better synchronized under SS. Similarly, fresh mass (FM) and dry mass (DM) of cotyledon, hypocotyl, and radicle were the highest in HP lettuce regardless of SS. Electrolyte leakage was the lowest in the HP lettuce, while other priming methods under SS increased membrane permeability, leading to osmotic stress and tissue damage. Overall, hydro-priming can be a good priming method for synchronizing germination and increasing FM and DM by creating the least osmotic stress and ion toxicity in lettuce under SS

Waterlogging Causes Early Modification in the Physiological Performance, Carotenoids, Chlorophylls, Proline, and Soluble Sugars of Cucumber Plants

Waterlogging occurs because of poor soil drainage and/or excessive rainfall and is a serious abiotic stress affecting plant growth because of declining oxygen supplied to submerged tissues. Although cucumber (Cucumis sativus L.) is sensitive to waterlogging, its ability to generate adventitious roots facilitates gas diffusion and increases plant survival when oxygen concentrations are low. To understand the physiological responses to waterlogging, a 10-day waterlogging experiment was conducted. The objective of this study was to measure the photosynthetic and key metabolites of cucumber plants under waterlogging conditions for 10 days. Plants were also harvested at the end of 10 days and analyzed for plant height (ht), leaf number and area, fresh mass (FM), dry mass (DM), chlorophyll (Chl), carotenoid (CAR), proline, and soluble sugars. Results indicated that cucumber plants subjected to the 10-day waterlogging stress conditions were stunted, had fewer leaves, and decreased leaf area, FM, and DM. There were differences in physiological performance, Chl, CAR, proline, and soluble sugars. Overall, waterlogging stress decreased net photosynthesis (A), having a negative effect on biomass accumulation. However, these decreases were also dependent on other factors, such as plant size, morphology, and water use efficiency (WUE) that played a role in the overall metabolism of the plant

The Effect of Environment and Nutrients on Hydroponic Lettuce Yield, Quality, and Phytonutrients

A study was conducted with green and red-leaf lettuce cultivars grown in a deep-water culture production system. Plants were seeded in rockwool and germinated under greenhouse conditions at 25/20 °C (day/night) for 21 days before transplanting. The experimental design was a randomized complete block with a 2 × 3 factorial arrangement of cultivar and nutrient treatments that consisted of six replications. Treatments consisted of two lettuce genotypes, (1) green (Winter Density) and (2) red (Rhazes), and three nutrient treatments containing electroconductivity (EC) levels of (1) 1.0; (2) 2.0; and (3) 4.0 mS·cm−1. After 50 days, plants were harvested, processed, and analyzed to determine marketable yield, biomass, plant height, stem diameter, phenolics, and elemental nutrient concentrations. An interaction between growing season and lettuce cultivar was the predominant factor influencing yield, biomass, and quality. Nutrient solution EC treatment significantly affected biomass and water content. EC treatments significantly impacted concentrations of 3-O-glucoside and uptake of phosphorous, potassium, iron, boron, zinc, and molybdenum. Effects of growing season and cultivar on leafy lettuce yield and quality were more pronounced than the effect of nutrient solution EC treatment. Thus, greenhouse production of green and red-leaf lettuce cultivars in the south-eastern United States should be conducted in the spring and fall growing seasons with elevated nutrient solution EC of ≈4.0 mS·cm−1 to maximize yield and quality

Effects of Elevated Temperature and Potassium on Biomass and Quality of Dark Red ‘Lollo Rosso’ Lettuce

Lettuce is an economically important crop for small and medium-sized growers. When grown in adverse environmental conditions, lettuce is vulnerable to a deterioration of yield and quality. Research concerning the impact of elevated potassium (K) levels on leafy vegetables, such as lettuce, is lacking. Therefore, seeds of dark-red ‘Lollo’ lettuce were germinated under greenhouse conditions at 25/20 °C (day/night). Plants were transferred into 11-L containers and placed into growth chambers at 25 and 33 °C. Plants were grown with K treatments of 117.3 (control), 234.6 (2×), 469.2 (4×), and 4) 938.4 (8×) mg·L−1. Increasing K treatments resulted in a negative quadratic response on lettuce dry mass and generated 14% more leaf calcium at 234.6 mg·L−1. An increase in temperature from 25 to 33 °C increased leaf dry matter and biomass by 40% and 43%, respectively. Leaf water content increased by 3% as temperature increased. Plants grown at 33 °C had greater quercetin glycosides compared to plants grown at 25 °C. The results from this study suggest that temperature is a stronger regulatory factor than increasing K in the determination of lettuce yield and quality. Increasing K concentration to 234.6 mg·L−1 results in greater concentrations of leaf minerals without compromising plant yield

Nitrogen Fertigation Rate and Foliar Urea Spray Affect Plant Growth, Nitrogen, and Carbohydrate Compositions of Encore Azalea ‘Chiffon’ Grown in Alternative Containers

The objective of this study was to investigate the plant vegetative growth, flower production, nitrogen (N) concentration, and carbohydrate compositions of Encore® azalea ‘Chiffon’ when fertigated with five N rates—0, 5, 10, 15, and 20 mM N—and grown in two types of containers, a black plastic and a biodegradable container, during one growing season. Foliar urea of 3% was applied to half of the plants in late fall to investigate its effect on plant N and carbohydrate concentrations. The paper biocontainers resulted in superior plant growth, increased plant size, dry weights, root length and surface area compared with the plastic containers with N rates of 10, 15, and 20 mM. The paper biocontainers also increased N uptake and carbohydrate concentrations mainly by increasing plant biomass. High N rates of 10 to 20 mM combined with urea spray and biocontainers generally resulted in the highest plant N concentrations. Foliar urea application in late fall tended to increase plant N concentration but decreased carbohydrates, including starch, glucose, fructose, and sucrose, to varying degrees, likely due to increased N assimilation. Fall foliar urea spray can be effective in improving the N status of azalea plants without affecting plant biomass

Influence of Nitrogen and Sulfur on Biomass Production and Carotenoid and Glucosinolate Concentrations in Watercress (\u3cem\u3eNasturtium officinale\u3c/em\u3e R. Br.)

Watercress (Nasturtium officinale R. Br.) is a perennial herb rich in the secondary metabolites of glucosinolates and carotenoids. 2-Phenethyl isothiocyanate, the predominate isothiocyanate hydrolysis product in watercress, can reduce carcinogen activation through inhibition of phase I enzymes and induction of phase II enzymes. Sulfur (S) and nitrogen (N) have been shown to influence concentrations of both glucosinolates and carotenoids in a variety of vegetable crops. Our research objectives were to determine how several levels of N and S fertility interact to affect watercress plant tissue biomass production, tissue C/N ratios, concentrations of plant pigments, and glucosinolate concentrations. Watercress was grown using nutrient solution culture under a three by three factorial arrangement, with three S (8, 16, and 32 mg/L) and three N (6, 56, and 106 mg/L) fertility concentrations. Watercress shoot tissue biomass, tissue %N, and tissue C/N ratios were influenced by N but were unaffected by changes in S concentrations or by the interaction of N × S. Tissue pigment concentrations of β-carotene, lutein, 5,6-epoxylutein, neoxanthin, zeaxanthin, and the chlorophyll pigments responded to changes in N treatment concentrations but were unaffected by S concentrations or through N × S interactions. Watercress tissue concentrations of aromatic, indole, and total glucosinolate concentrations responded to changes in N treatments; whereas aliphatic, aromatic, and total glucosinolates responded to changes in S treatment concentrations. Individual glucosinolates of glucobrassicin, 4-methoxyglucobrassicin, and gluconasturriin responded to N fertility treatments, while gluconapin, glucobrassicin, and gluconasturiin responded to changes in S fertility concentrations. Increases in carotenoid and glucosinolate concentrations through fertility management would be expected to influence the nutritional value of watercress in human diets

Morphological and Physiological Response of Different Lettuce Genotypes to Salt Stress

Salt stress (SS) refers to excessive soluble salt concentrations in the plant root zone. SS also causes cellular water deficits, ion toxicity, and oxidative stress in plants, all of which can cause growth inhibition, molecular damage, and even plant mortality. Lettuce (Lactuca sativa L.) has a threshold electrical conductivity of 1.3–2.0 dS/m. Thus, this research focused on physiological, morphological, and biochemical attributes in multiple lettuce genotypes under SS compared to plants grown under control conditions. The experiment was arranged in a randomized complete block design with four replications. One month after planting, the salt treatment was applied at the rate of 100 millimoles (mM). The 0 mM salt in water treatment was considered the control. A significant effect of SS on different morphological and physiological traits was observed in one-month-old lettuce plants. PI 212099, Buttercrunch-1, and PI 171676 were highly salt-tolerant. Genotypes with high salt tolerance usually had poor growth potential under control conditions. This suggests that the morphological and physiological response of 38 lettuce cultivars towards SS is genotype dependent. Identifying SS’s physiological, morphological, and biochemical attributes in lettuce may help plant-breeders develop salt-tolerant lettuce genotypes

Lettuce Biomass Accumulation and Phytonutrient Concentrations Are Influenced by Genotype, N Application Rate and Location

The purpose of this research is to determine how increasing levels of nitrogen (N) fertilizers, locations, and cultivars affected yields, biomass accumulation, and polyphenol concentrations in lettuce. This study is carried out at the North Mississippi Research and Extension Center (NMREC) and Northwest Washington Research and Extension Center (NWREC). The experiment is a randomized complete block design arranged in a 2 × 2 × 4 factorial with 4 replications. Treatments include two cos (romaine) lettuce cultivars, ‘Salvius’ and ‘Thurinus’. N treatments include 42, 63, 105 and 189 kg·ha−1. ‘Salvius’ has greater fresh mass (FM) and dry mass (DM), and a smaller DM:FM ratio when compared to ‘Thurinus’. The NWREC location has higher lettuce FM and DM. Quercetin-3-glucoside (Q-3-G) increases with increasing N concentrations. There are interactions between locations and lettuce cultivars for chlorogenic acid, Q-3-G, and quercetin/luteolin glucuronide (QL-G). There is increased chlorogenic acid content in ‘Salvius’ at the NMREC and increased concentrations of Q-3-G and QL-G in ‘Thurinus’ compared to the NWREC location. ‘Thurinus’ has significantly more chicoric acid and quercetin-malonyl-glucoside (QM-G) than ‘Salvius’. Lettuce at the NWREC has significantly more chicoric acid and cyanidin-3-glucoside (C-3-G). Lettuce at the NWREC has greater yields and biomass accumulation. Lettuce at the NWREC also has greater amounts of flavonoids and anthocyanins. ‘Salvius’ has greater amounts of phenolic acids and ‘Thurinus’ has greater amounts of flavonoids and anthocyanins

Individual and Interactive Temporal Implications of UV-B Radiation and Elevated CO2 on the Morphology of Basil (Ocimum basilicum L.)

Temporal and spatial variations in ozone levels and temporal changes in solar radiation greatly influence ultraviolet radiation incidence to crops throughout their growth, yet the interactive effects of CO2 and UV-B radiation on Basil production under sunlight environmental conditions has not been studied. Basil ‘Genovese’ plants grown under sunlit plant growth chambers were subjected to a combination of supplemental UV-B (0 and 10 kJ m−2d−1) and ambient (420 ppm) and elevated (720 ppm) CO2 treatments for 38 days after 14 days of germination. UV-B radiation treatments caused a decrease in basil stem branching, fresh mass, and stem dry mass under both CO2 treatments when harvested after 17 and 38 days of treatment. There was also an increase in basil leaf surface wax under UV-B (10 kJ m−2d−1) treatment compared to controls (0 kJ m−2d−1). Elevated CO2 treatments caused a decrease in morphological features, including specific leaf area and fresh mass. Interactive effects between UV-B and CO2 treatments existed for some morphological features, including plant height, root surface area, and average root diameter. Understanding the impacts that CO2 and UV-B radiation treatments have on basilcan improve existing varieties for increased tolerance while simultaneously improving yield, plant morphology, and physiology

Yield, Physiological Performance, and Phytochemistry of Basil (Ocimum basilicum L.) under Temperature Stress and Elevated CO2 Concentrations

Early season sowing is one of the methods for avoiding yield loss for basil due to high temperatures. However, basil could be exposed to sub-optimal temperatures by planting it earlier in the season. Thus, an experiment was conducted that examines how temperature changes and carbon dioxide (CO2) levels affect basil growth, development, and phytonutrient concentrations in a controlled environment. The experiment simulated temperature stress, low (20/12 °C), and high (38/30 °C), under ambient (420 ppm) and elevated (720 ppm) CO2 concentrations. Low-temperature stress prompted the rapid closure of stomata resulting in a 21% decline in net photosynthesis. Chlorophylls and carotenoids decreased when elevated CO2 interacted with low-temperature stress. Basil exhibited an increase in stomatal conductance, intercellular CO2 concentration, apparent quantum yield, maximum photosystem II efficiency, and maximum net photosynthesis rate when subjected to high-temperature stress. Under elevated CO2, increasing the growth temperature from 30/22 °C to 38/30 °C markedly increased the antioxidants content of basil. Taken together, the evidence from this research recommends that varying the growth temperature of basil plants can significantly affect the growth and development rates compared to increasing the CO2 concentrations, which mitigates the adverse effects of temperature stress