Document Type : Full Paper

Authors

• Parnia Pakan ¹
• Mansour Gholami ¹
• Abdolkarim Chehregani Rad ²
• Hassan Sarikhani ¹

¹ Department of Horticultural Science, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran.

² Department of Biology, Faculty of Science, Bu-Ali Sina University, Hamedan, Iran.

Abstract

Keywords

• Flower number
• fruit weight
• LED light
• stomatal conductivity
• strawberry

Main Subjects

• Fruit Science

Extended Abstract

Introduction

Strawberry is one of the most valuable crops, widely consumed in the world. Because of its nutritional value and taste, the demand for its production and consumption has extensively been increased; consequently, improving its fruit composition is of great importance. After producing off-season strawberry in the last 20 years, the growers have developed different methods in strawberry production under greenhouse condition. In this regard, a controlled environment can provide an opportunity to produce strawberry in the off-season. It generally requires a long day and a suitable light intensity to gain suitable growth and development. Regarding the existence of low light and short-day length, predominant in a vast majority of the strawberry-producing greenhouses, employing supplemental lighting is crucial on inducing plants’ growth and flowering. Light characteristics (i.e., intensity, quality, and duration) play an important role in regulating strawberry’s growth, development, flowering, and photomorphogenesis. As a main source of energy for photosynthesis in plants, light usually stimulates some changes in gene expression, physiological, morphological, and metabolic characteristics through photoreceptors. Strawberry cv. 'Camarosa' is a short-day plant in which vegetative growth is influenced by day length and temperature. The present study aimed to evaluate the effect of the quality of supplemental light on the morphological and photosynthetic characteristics of strawberry cv. 'Camarosa' under greenhouse condition.

Materials and Methods

This research was carried out in the research greenhouses of the Department of Horticultural Sciences, Bu-Ali Sina University in the autumn and winter seasons. The plants of strawberry cv. 'Camarosa' were initially transferred to the greenhouse and cultivated in a hydroponic bed containing cocopeat and perlite (70:30 ratio). Afterwards, they were fed three days interval using Hoagland nutrient solution. During the experiment, the environmental condition inside the greenhouse was adjusted as follows: temperature (25°C day/15°C night), relative humidity (70%), and the period of natural lighting 11 h per day/13 h per night on average. The experiment was conducted as a completely randomized design with three replications. A total of six treatments of this experiment included 100% red light (660 nm) (100% RL), 100% blue light (440 nm) (100% BL), 83% red light +17% blue light (83% RL + 17% BL), 67% red light + 33% blue light (67% RL + 33% BL), 50% red light + 50% blue light (50% RL + 50% BL), and daily sunlight (DS) as control. Lighting with an approximately intensity of 250 μmol/m²/s was supplied with light emitting diodes (LED) and sunlight (800 to 1000 μmol/m²/s) for 14 hours from 5 am to 7 pm. Finally, some morphological characteristics and photosynthetic parameters of strawberry were measured after about one month of supplemental lighting.

Results and Discussion

Results of this study revealed that our treatments were effective on the morphological characteristics including petiole length, leaf area, flower number, flower petiole length, runner number, runner length, crown diameter, and leaf number. The highest leaf number, petiole length, leaf surface, flower number, runner number, and crown diameter were observed in the plants subjected to 100% BL  and 50% RL + 50% BL, respectively. Except for runner length, both lightings of 100% RL and DS (control) had no significant difference on the growth parameters. Overall, supplemental lighting was found to have a significant impact on the content of chlorophyll a, b, total, and total carotenoids. As such, the highest increase in chlorophyll content was belonged to the 100% BL, followed by 50% BL as well as 50% RL, as compared with DS. Moreover, no significant difference was found between 67% RL+33% BL and 84% RL +16% BL in terms of photosynthetic pigments. Although exposing the plants to the 100% RL increased both chlorophyll and carotenoid content in comparison with the control, no significant difference was recorded between them. In addition, lighting 100% BL significantly amplified photosynthetic activity, stomatal conductance, sub-stomatal CO₂, and water use efficiency (WUE), while the 100% RL and the control reduced the above-mentioned physiological characteristics.

Conclusion

    The results of this study provide evidence on the efficiency of supplemental lighting using LEDs for improving growth parameters and morphological characteristics of strawberry cv. 'Camarosa'. In this context, supplemental lighting could activate the metabolic pathways related to the production of photosynthetic pigments, improve stomatal exchange, and increase the rate of photosynthetic activity.