Effect of various LED light on the growth and reproductive of in vitro-derived Indonesian chili pepper (Capsicum annum) Kopay and Laris varieties

Red chili (Capsicum annuum), is one of the horticultural commodities that has a high demand. The production, however, is limited because of unsuitable climate and pest attack. Artificial light using LED light in indoor farming is a potential approach to solve the problem and for the production of metabolites for human health. The aim of this research was to evaluate the effect of various LED lights (white, red, blue, UV and combination red+blue) on two Indonesian chili pepper (Capsicum annuum) varieties Kopay and Laris derived from in vitro cultures and grown in the growth chamber and the greenhouse. Parameters observed were leaves number, plant height, number and weight of axillary buds, number of flower and number of young fruits. The results showed that Laris and Kopay under red and blue light significantly different on height character at 66 DAT. In Laris variety, the highest leaves number observed in plants under red light, while the highest young fruit number observed under blue light. Both red and blue lights grew taller than white light. In Kopay variety, combination red+blue light resulted in higher value in plant height, number of flowers has bloomed, number of axillary buds and weight of axillary buds at 37 DAT. The highest young fruit number observed in plants under white light. These results demonstrated that light wavelength through LED light affected plant growth and development. The findings are crucial for determining the best treatment for producing fruits containing health related-metabolites accumulated in chili peppers of each variety.


Introduction
Chili (Capsicum annuum L.) is one of horticultural crops that is in high demand in Indonesia.Chili has a favorable economic outlook, because of increasing demand of household needs, food industry and pharmaceuticals in harmony with the increase of population (1).Chili can be consumed in the form of fresh fruit, or dry as a cooking spice and also as an industrial raw material for the food, poultry feed and pharmaceutical industries.Chili contains many nutrients and considered as a source of vitamin A, C, E, carbohydrate, protein, fat, minerals, carotenoid, oleoresin, phenol and capsaicinoid (2,3).
However, chili production is greatly affected by the environment, pest and disease attacks.One of solutions is to grow plants indoors.However, light is a limiting factor in indoor gardening.Light is needed by plants to carry out photosynthesis.The solution to overcome this is the use of artificial light energy.Light-emitting diodes (LED) is an alternative for artificial greenhouse lighting with numerous advantages.The advantages of Light-Emitting Diodes (LEDs) are wavelength specificity, less heat IOP Publishing doi:10.1088/1755-1315/1255/1/012047 2 radiation, cooler emitting temperature, longest durability, lower energy consumption, and the possibility to manipulate the spectral qualities of the emitted light (4,5).
Light can affect the growth of plants through the regulation of photosynthesis.The wavelength of light is the main factor affecting the development of the photosynthetic machinery and photosynthesis efficiency (6).In addition to providing the energy for photosynthesis, other roles of light have been on plant development and metabolism as it also dictates specific signals which regulate plant development, shaping and metabolism, in the complex phenomenon of photomorphogenesis, driven by light colours (7).The wavelength of red and blue lights are the primary focus of current research because of their regulatory effect on plant development.Red light (660 nm) is efficiently absorbed by plant photosynthetic pigments (chlorophyll and carotenoids) and stimulates phytochrome photoreceptors.The blue light (400-500 nm) performs a variety of important photomorphogenic roles in plants, including stomatal opening, stem elongation, and phototropism (8).
Responses of LED light vary according to plant species.Various effects of LED lights have been studied in some crops such as pakcoy (9), growth and development in vitro plantlet of vanilla (10), growth of seedling of hybrid tomato (11) and growth, development and mineral content in okra (12).The effect of light spectrum of artificial lighting on plant growth and photomorphogenesis in vegetable and ornamental crops has been reviewed (7).The study conducted was the first research on Indonesia chili pepper var.Laris and Kopay.The research was carried out to understand the effect of different LED lights (white, red, blue, UV and combination red and blue) on the growth and fruit development of in vitro-derived Indonesian chili pepper var.Laris and Kopay plants grown in different compartment (growth chamber and greenhouse).

Plant materials
The genetic materials used in this study are seeds of C. annuum varieties, Laris and Kopay, which were obtained commercially and were cultured under various light treatments.Five seeds per treatment with two replicates were sterilized in 70% (v/v) ethanol for 5 min and rinsed with distilled water three times.Seed were soaked in 30% (v/v) hypochlorite solution (5 min) and rinsed with sterile distilled water thrice.Seeds were dried on sterile tissue papers.

Light treatments
The seeds were germinated on Murashige and Skoog (MS) hormone-free media and cultured under lights with different wavelengths as compared to the white light (LED lamp 9 Watt / 110-265Voltage, MORGEN GRAN MG-GY5A09) as a control for 7 weeks.Other lights colours compared were red (infrared lamp PHILIPS 100 Watt (220-240Voltage), blue (LED lamp of TL PHILIPS 18 Watt (110-265Voltage), and combination of red and blue (LED red + blue 10 Watt, 5 Watt voltage).Lights duration of white, red, blue and combination red blue was 12 hours per day.UV light treatment was applied on chili seeds in clear plastic bag using UV light source inside Laminar Air Flow Cabinet for 8 hours.The treated UV light seeds were then surface sterilized and germinated on MS hormone-free medium.

Germination
Further germination was conducted by subculturing the elongated shoots on MS hormone-free medium.Subculture was conducted several times depending on the growth rate of each cuttings using the same media composition.The temperature and photoperiod conditions in the culture room were 25 o C and 16 hours photoperiod, respectively.After the shoots produced 2-3 roots, the plantlets were acclimatized in the growth chamber.

Growth maintenance
The plantlets were transferred to a 32 well tray containing a mixture of soil+vermiculite+perlite (1:1:1).The plants were covered for two weeks and grown in a Reach-in Growth Chamber (Conviron Ltd.).The plants were fertilized with NPK at the ratio of 20:10:20 every week at the age of 3 weeks after transplanting.The plants were transferred to an individual 6-inches at 4 weeks old.At 53 DAT, the plants were transplanted to a larger pot (12 inches in diameter) containing the same composition of media in the greenhouse containment.The plants were fertilized using NPK at the ratio of 20:10:20 every two weeks.The temperature and photoperiod were set to 22-25 o C and 16 hours, respectively.The plants were watered daily.

Observation and data analysis
The characters observed were the vegetative characters and reproductive characters.The vegetative characters were: plant height, number of leaves, and number of axillary buds, while the reproductive characters were: number of flower and number of young fruits.The observation was conducted from 23 DAT until 104 DAT.Data were analyzed using SPSS statistical program and compared using Duncan at a probability level of 0.05.

Results and Discussion
Different lights had different effects on the number of leaves and plant height (Table 1).The plants of Laris variety grown under red light showed more leaf number than that were grown under white and blue light.In Kopay, blue light resulted in the lowest number of leaves as compared to other light treatments.This result is in accordance with the result of the study in okra plant that showed blue light give the lowest number of leaves than red and green (12).
At 23 and 27 day after transplanting (DAT), control plant of Laris which were cultured under white light were taller than blue and red light.This is in line with Javanmardi study (13) who showed that tomato and pepper seedling under full white light had the highest plant height as compared to that under red and blue light alone or in combination.However, the phenomenon was only occurring up to the third week of the growth, as at 66 DAT there was a change in the height of plants of Laris as those have been treated in red and blue light were taller than the others.The study in pachoy under white light showed the stems do not grow as high as other lighting because of inhibition of auxin hormones in plants, which causes the plants to grow slowly (14).The increase of plant height from 27 DAT to 66 DAT was more than 20 cm (Figure 1).Degny (12) stated that there is an evolution in leaf area and plant height in okra indicated by plants in blue light in 30 days were similar to other treatments, but at 38 days started to differentiate from other light treatments in stimulating a better response in plants for leaf area and plant height.Plants take in all colors and wavelength of light, however some colors affect the plant species more than others (14).The wavelength of light that match the needs of plants can support plant growth and development.Plant growth is strongly influenced by the spectrum of light received by plants (15).Axillary bud is formed at the junction between leaf and stem of the plants.The white LED resulted in a higher number of axillary buds (6.0 and 4.7) than red and blue light colors both in Laris and Kopay (Table 2).This implies that white light promoted bushy growth as more vegetative organs than other light colors which might delay flowering.In Kopay, a combination of red and blue light gave result in a higher number of axillary buds than the white light.
Pruning the chili pepper plant is an effort that is practiced by farmers to obtain plant with better fruit quality.Pruning aims to reduce the number of buds, shoots or branches that are not productive, so the growth of the fruit can be maximized (16).In this study the axillary buds were pruned (removed) and weighed to measure the difference in addition to the number of the buds as some plants produced a higher number although the size buds was varied.Flower formation is critical for plant fruit development.In present study, blue light led to the lowest number of flower in Kopay variety (Table 3).In contrast, Nie (17) reported that the number of flower in pepper plants grown under blue light was much higher than that under red light.The difference might be greatly due to the different species or varieties used.Blue, white, and red lights did not affect flowering time and number of flowers of Laris as no flower buds were observed at 62 DAT indicating that genetic factor is more dominant.Laris is considered as late flowering among Indonesian chili pepper varieties which will be flowering at the age about 65 days after transplanting, while Kopay 35 days after transplanting (18).Flower formation is influenced by many factors, so the flowering time can be longer.Laris variety was chosen due to its fruit long transportation durability and its resistant to bacterial blight in addition to its wide spectrum of ecosystem from lowlad to highland.In certain species, light quality could be manipulated not only to increase the number or the weight of organs but also to enhance targeted compound concentrations for various purposes as reported by other researchers.Carvalho (19) concluded that light quality could change the type and the amount of specific compounds in Ocimum basilicum.At 104 DAT the fruit number of the control (white light) of Kopay chilli pepper was the highest whereas Laris treated with red color produced no fruit (Table 4).Although there were many flowers produced, but most of the flowers dried and fell of without forming fruits.Laris variety plants produced the highest number of fruit (2 fruit) when they were treated with blue light then followed by white light (control).Meanwhile, chili pepper of Kopay variety produced the highest number of fruit when white light was used then followed by red light.Formation of fruit is controlled by many factors.Plants are most effective in carrying out the process of photosynthesis under white light, which includes all wavelength (19).White light consists of all color spectrum, so it provides some spectrum of light needed by plants (14).Kopay seems to be superior to Laris in terms of reproductive phase which was reflected by the higher number of fruit than Laris.Genetics or the nature of these varieties have greatly influenced the yield as they were grown and maintained in the same conditions in the greenhouse.Laris is a national variety which is considered a late flowering variety and late maturing fruits than Kopay.The latter one has been a favorite variety in West Sumatra Province which is well known for hot or spicy food.

Conclusions
Our results showed that Laris and Kopay varieties under red and blue light were significantly different in terms of height at 66 DAT.In vegetative stage, Laris variety under these light spectrums produced taller plants.Whereas Kopay plants grew taller under the combination of red+blue ligh which also beneficial for reproductive stage indicated by the highest value of number of flowers have bloomed.While Laris variety had no flower on all lighting conditions.Kopay under white light produced more young fruits than others indicating that reproductive stage is influenced by genotypic factor.The findings are not only crucial for determining the best treatment for producing fruits containing health related-metabolites accumulated in chili peppers of each variety, but also for the improvement of agricultural practices using in vitro culture-derived plants.Further research to assess the yield, the effect on the multiplication of the second generation and genetic stability is required and will be conducted.

Figure 1 .Table 2 .
Figure 1.Plant Height at 27 DAT and 66 DAT and increasing of plant height of chili pepper var.Laris and Kopay.( L=Laris, K=Kopay)Table 2. Effect of light on the average of number and the weight of axillary buds of Indonesian chili pepper var.Laris and Kopay Treatments No.of samples Number of Axillary buds at 29 DAT

Table 1 .
Effect of light on the average number of leaves and the height of Indonesian chili pepper var. doi:10.1088/1755-1315/1255/1/012047

Table 3 .
The effect of LED light color on the average of flower number at 62 DAT of Indonesian chili pepper var.Laris and Kopay

Table 4 .
The effect of LED light color on the average of fruit number of Indonesian chili pepper var.Laris and Kopay Different letters in the same column indicate significant differences (p<0.05) based on the Duncan's multiple range test