International Journal of Horticultural Science and Technology
Volume:10 Issue: 4, Autumn 2023

Intumescence is a physiological disorder in which cell walls are disrupted. Intumescence causes leaf deformation, browning and defoliation, and commonly affects tomato plants. This is a limitation in seedling production. The causes of intumescence are not known; however, ultraviolet (UV) deficiency is considered as one of the causes of intumescence. Other possible causes include high humidity and rapid changes in the water environment. In this study, tomato seedlings were grown in a commercially-available closed seedling production system under either newly installed LEDs with a low UV light intensity or conventional fluorescent lamps sources. The relationship between the shoot/root (S/R) ratio and incidence of intumescence was evaluated. In addition, the effects of different light sources were evaluated on the xylem pressure potential in the seedlings under rapidly fluctuating water conditions. As a result, the S/R ratio of seedlings grown under LEDs, with low UV intensity, was greater than that of seedlings grown under fluorescent lamps. There was a positive correlation between the S/R ratio and the incidence of intumescence of four types of seedlings with different combinations of light sources and varieties. Xylem pressure potential decreased more in seedlings grown under LEDs, compared to seedlings grown under fluorescent lamps and dry conditions, but increased significantly when irrigated. These results suggest that reducing the occurrence of intumescence in seedling production systems can be possible by a light source that can help seedlings grow with small S/R ratios and reduce fluctuations in the water condition.

As a valuable industrial compound, cichoric acid has antiviral, antioxidant, and anti-inflammatory properties. It is effectively used in obesity prevention and for neuroprotective purposes. Here, we aimed to compare the effects of plant growth regulators and UV-B radiation on the induction of cichoric acid production under tissue culture conditions. For this purpose, Lactuca undulata, an herbaceous medicinal plant, was used as a new source of cichoric acid. Leaf explants were initially cultured on ½ MS (Murashige and Skoog) medium containing 0.1, 1 mg/L Kinetin (Kin) and 2,4-Dichlorophenoxyacetic acid (2,4-D). The callus was then exposed to different UV-B exposure times (0, 20, 40, and 60 min) and was harvested after 5, 10, and 15 days. The highest amounts of total phenol, cichoric acid, chlorogenic acid, and caffeic acid were achieved in callus samples that were treated with 20 and 40 minutes of UV-B radiation for 10 days. Cichoric acid content reached an amount of 6.15±0.292 mg/g DW after 20 min of radiation. Pearson’s correlation coefficient analysis (PCC) showed that Phenylalanine Ammonia Lyase (PAL) activity did not correlate with the production of caffeic acid derivatives. These results suggested that UV-B irradiation can be used as an elicitor to induce the production of cichoric acid in Lactuca undulata callus cultures.

The massive establishment of new plantations supported by the basic needs of a crop are technical approaches for an increased crop productivity. Water and decreased light levels by shade (i.e. intercropping) are considered basic needs of cacao plants, especially during the early vegetative growth stage. Thus, this study aimed to evaluate the influences of irrigation, intercropping, and intercrops on the performance of 39 cacao plantations at the establishment phase. The performance of each cacao plantation, after establishment, was evaluated and rated from 1 to 7 (1- poor; 3- satisfactory; 5- very good; and 7- outstanding) as a rating scale. In general, the results revealed that cacao plantations supplied with irrigation or under decreased light levels by intercrops (regardless of their nature), as well as a combination of these, made the plants perform better than those in plantations without irrigation and when plants were highly exposed to sunlight. The results suggested the importance of irrigation and decreased light levels by intercropping as prerequisites for a successful establishment of cacao plantations.

A prevalent problem in pomegranate fruit is sun damage that decreases the quantity and quality of fruit. This study's objective was to evaluate the effect of different photo-selective shade net colors and shading percentages on growth traits and pomegranate fruit quality during two-years (2019 and 2020). Plots of pomegranate trees (cv. Malse Saveh) were covered to full canopy with two colors photo-selective shade nets (White and Green) and with two shading percent (30 and 50%) compared to uncovered plots (control) at Saveh region in the same orchard at the time of fruit set (10 June) and maintained on the trees for four months. The findings showed that shade nets increased relative leaf water content while decreasing temperature and light intensity in the canopy and fruits as compared to the control. Pomegranates maintained under nets had much higher fruit weight and yield than those uncover trees. The percentage of sunburn fruits was dramatically reduced when a shade net was used. In uncovered trees, the percentage of sunburn was 27.85 %, whereas in shade treatments, the percentage of sunburn was at 0 - 4.5%. The white shade net 50% PAR (Photosynthetically active radiation) had the highest fruit weight, juice percentage, aril weight and yield, maximum color of fruits and arils, as well as the lowest level of proline content among the shading treatments. The highest amount of total anthocyanin (55.13 mg/100 mL), total phenolics (34 mg GAE/100 mL) and vitamin C (21.32 mg/100 mL) was observed under white shade net 50% PAR.

Acclimation to the privilege lighting environment is an important step for survival of newly developed horticultural plants such as for transplants, tissue culture-generated plants and for mature plants when there is a change in the light intensity during the growth period or even during the course of one day. Excess light energy capture without antecedent acclimation imposes photooxidative cellular damage and photoinhibition. Absorption of excess light beyond the capacity for photosynthetic electron transport is harmful to photosynthetic organisms. However, plants are equipped with photoprotective mechanisms to attenuate the detrimental effect of excess light energy on the photosynthesis apparatus. In this review, we discussed how different controlled environment horticulture (CEH) systems presented lots of opportunities for improving yield and quality, and the current understanding of the direct and indirect functional roles of light spectra in the regulation of photoinhibition and photoprotection are discussed.

In the past decade, light-emitting diodes (LEDs), as a suitable replacement for many other types of light sources, have attracted lots of attention. Supplemental lighting improves growth and yield of greenhouse vegetables such as sweet pepper, cucumber and tomato in all-year round. In the present study, to investigate the quality of LED lighting on sweet pepper seedlings, the effects of three combinations of red (R) and blue (B) LEDs (R90B10, R80B20, and R70B30, with light intensity of 200 μmolm-2s-1 for all LED light treatments) were studied on the growth and photosynthesis functionality of two greenhouse sweet pepper cultivars (̒Padra̓ and ̒Shadleen̓) under two growing seasons of winter and summer in Rasht, Iran (latitude ˜ 37 °N). Thicker stems, wider leaf area, higher biomass, as well as improved photosynthetic functionality were detected in seedlings exposed to the supplemental lights. An increase in the ratio of B light led to positive effects on the growth and photosynthesis functionality of the seedlings. However, no significant difference was observed between the cultivars. The effect of supplemental light was more emphasized in the winter. In this way, the control seedlings were weak and pale, while strong seedlings with dark green leaves were produced under the supplemental light. In conclusion, supplemental LED lighting was presented as a practical tool for the commercial production of greenhouse seedlings

Increasing day length during the short photoperiod in fall and winter is a beneficial means of increasing biomass production and altering plant morphology and phytochemistry. The objective of this study was to investigate the effects of light quality at the end of the day (EoD) on the growth and phytochemical characteristics of lemon balm. During short-day photoperiods in autumn, lemon balm (Melissa officinalis L.) seedlings were exposed to red, blue, and combined red/blue light using light-emitting diodes for 2 hours at the EoD and then compared with the control. The results showed that exposure to red light significantly increased biomass. Plants grown under blue light yielded the highest percentage of dry matter, and their leaves had the highest content of chlorophyll and flavonoids. In addition, the highest contents of carotenoids were found in the plants irradiated with blue light and later with red+blue light. The highest levels of total phenols, anthocyanins, and antioxidant activity were found in the plants grown under red light. In addition, light quality had a significant effect on essential oil content. The highest essential oil content was obtained in the red and red+blue light treatments. The light quality at the EoD significantly changed the essential oil composition. The blue light significantly increased the citronellal content but decreased the geranial and linalool content. This study provides insight into the effects of EoD light quality on plant growth and metabolite accumulation in lemon balm during a short photoperiod.

In this present study, the influence of three-wide spectrum light-emitting diodes (LEDs), emitting warm light AP67 (moderate blue and red and low red:far-red), AP673L (high red and high red:far-red) and G2 (high red and low red:far-red) with different colours mixing blue, green, red and far-red was used for micropropagation of three Polish potato cultivars; ‘Aruba’, ‘Oberon’ and ‘Skawa’. The planlets were grown in a growth room with a 16-h photoperiod, the photosynthetic photon flux density was set at 30 μmol m-2 s-1. The tissue culture medium applied for shoots proliferation was a standard MS-based medium, microtuberization was performed on MS medium supplemented with higher sugar content (40 mg/L-1). Light quality affected the number of microtubers (MTs) per plantlet, the volume (cm3) of MTs, the fresh weight (mg) of MTs and the width (mm) of MTs. Different light qualities did not affected morphological parameters including length (mm), perimeter (mm), and cross-section area (mm2) of microtubers, while the highest number of microtuber were detected under AP67 light quality. The morphological parameters were mostly dependent on the cultivar. The lowest number of microtubers were observed under G2 treatment. In conclusion, ‘Aruba’, as well as ‘Oberon’ with AP67 and AP673L, LED lighting systems were determined to be most suitable in terms of the number of MTs per plantlet, volume (cm3), fresh weight (mg) and width (mm) of MTs.

Kale, which has anti-cancer properties, is rich in nutrients and antioxidants. The increase in lifestyle diseases has encouraged the inclusion of Kale in healthy diets. Light plays a major role in plant growth. This study determined the effects on kale under different light conditions in terms of morphological, yield, and physiological responses. The treatments used in this study were: Ambient Light (AL) and 16:8 light-dark periods scheme on Red LED (RL), Green LED (GL), and Blue LED (BL) six days before harvesting. Kale grown under GL and BL produced the tallest plant that was four times longer than AL. However, in the number, length and width of leaves, AL was found to be greater than the seedlings grown under controlled lights. On yield responses, no significant differences were noted on fresh weight, dry weight, and computed yield. On physiological responses, RL, GL, and BL all increase the average vapor pressure deficit. In terms of average photosynthetic rate, BL’s performance is better than those exposed to AL. However, AL’s stomatal conductance resulted in a greater amount than plants exposed to LED lights. The average transpiration rate showed improvement under RL. These results suggest that GL and BL are most suited for plant height development while AL enhances the number, length, and width of leaves. Moreover, when grown under BL, photosynthetic rate was enhanced. On the other hand, exposure to AL improved stomatal conductance. Increased photosynthetic rate where implicated to enhance secondary metabolite such as glucosinolate to which Kale are sought after.

Optimizing light and nutrient circumstances has a key role in seedling quality and yield performance of cucumber seedling. The combined effects of light quality {blue (B), white [W; 41 % B, 39 % intermediate, and 20 % red (R)], RB [red (80 %) and blue (20%)], and R} and nutrient solution EC (1, 1.7, and 3 dS m-1) on the growth and physiological responses of cucumber seedlings (as a model plant) were studied. Growth, biomass distribution, water status, seedling quality, yield, and concentration of photosynthetic pigments, protein, proline, and elements (K, P) were evaluated. The results showed that the effects of light quality on cucumber were dependent on nutrient solution EC. RB treatment at EC 1.7 irrigation had the highest value of seedling quality parameters and utmost amount of osmolytes, elements and pigments, showing adequate water performance. Moreover, in contrast to the conventional seedling production, yield and biomass production increased by 70% and 92%, respectively, in the transplanting phase, which was due to better element uptake, higher biomass distribution, and low vegetative growth in the seedling production phase. These results can contribute to seedling production of vegetables as an efficient protocol for yield productivity. Together, our findings show that when determining the ideal light spectrum for cucumber seedling growth, the nutrient solution EC should be considered.