Studies on effect of light spectrum and photoperiod interaction on acceleration flowering and performance on chilli (Capsicum annum L.) genotypes under indoor vertical systems

Introduction

Chilli (Capsicum annuum L.) belonging to the family Solanaceae with chromosome number 2n=2x=24, is one of the most widely cultivated vegetable and spice crops across the world. It is primarily grown for its pungent green and ripe fruits, which are commonly used as vegetables, condiments, spices, and pickles. Chilli fruits are extensively utilized in culinary preparations to enhance flavour, colour, and pungency in food products. In addition to their culinary importance, chillies are considered a valuable source of vitamins A, C and E, along with several antioxidants and bioactive compounds beneficial for human health. Consumption of chilli is associated with various health-promoting effects such as improving immunity, supporting cardiovascular health, aiding metabolism, and assisting in weight management. The presence of capsaicin in chilli contributes to its medicinal properties and has been widely used in pharmaceutical formulations and therapeutic preparations for ailments such as cold, sore throat, asthma, chest congestion, headaches, and arthritis. In addition to its nutritional and medicinal importance, chilli holds a prominent position in the agricultural economy and food processing industry. The crop is widely utilized in different forms such as fresh fruits, dried pods, powders, sauces, and other processed products to improve the flavour, colour, and pungency of food preparations. Chilli cultivation plays a vital role in generating employment opportunities and serves as a significant source of income for farmers in several countries, particularly in India. Owing to its adaptability to varied climatic conditions, high consumer demand, and considerable export value, chilli is recognized as one of the most economically important spice crops cultivated across the world. Chilli is one of the most widely cultivated spice crops in the world, with a global production of nearly 7 million tonnes grown over an area of approximately 1.5 million hectares. India occupies a leading position in chilli production, followed by countries such as China and Pakistan, indicating the major contribution of Asian nations to global chilli cultivation. Although chilli is produced across many parts of the world, the highest consumption and demand are observed in countries including India, China, Mexico, Thailand, the United States, the United Kingdom, Germany, and Sweden. Among the cultivated species, Capsicum annuum is the most widely grown and commercially important species, while certain pungent types belong to Capsicum frutescens. Chilli is extensively used as a spice in various cuisines to impart characteristic pungency, flavour, and colour to food preparations and sauces. The pungent nature of chilli is mainly attributed to the presence of capsaicin and other related compounds collectively known as capsaicinoids.

Research related to indoor crop production has primarily emphasized the role of environmental factors such as light quality, light intensity, and photoperiod in regulating plant growth and productivity. Among these factors, light plays a crucial role in controlled environment agriculture due to its direct influence on photosynthesis and plant developmental processes. Variations in light conditions can significantly affect plant growth characteristics including stem thickness, branching pattern, rooting behaviour, seed germination, and flowering responses. Recent studies have demonstrated that the use of supplemental lighting with different spectral compositions, such as UV-A, blue, green, red, far-red, and white LED lights, can markedly influence the accumulation of phytochemical compounds including anthocyanins, carotenoids, chlorophylls, and flavonoids in leafy vegetables like lettuce. The synthesis of carotenoids in fruits and vegetables is strongly influenced by both light intensity and spectral quality. Furthermore, in greenhouse cultivation systems, the limited availability of UV-B radiation may alter flavonoid concentration in leafy crops, thereby affecting their flavour, nutritional quality, and visual appearance.

Materials and Methods

The present investigation entitled "Studies on effect of light spectrum and photoperiod interaction on accelerated flowering and performance on chilli genotypes (Capscicum annum L.) under indoor vertical systems" was conducted during the year 2025-2026 at Urban Kisaan Private Limited, Gundlapochampally, Hyderabad, Telangana, India. The experiment was carried out under a controlled indoor cultivation system to evaluate the influence of different light spectrum and photoperiods on the growth and flowering performance of arugula. Two arugula varieties, namely Thai chilli and Bullet chilli were subjected to varying combinations of red and blue LED light treatments under 14-hour and 16-hour photoperiods. The materials employed and the experimental procedures adopted for conducting the study are described in the following sections.

Experimental Design

The experiment was laid out in a Factorial Completely Randomized Design (FCRD) with ten treatments and 3 replications. Each treatment consisted of 30 plants established in pots arranged across vertical layers. One plant pot were randomly selected and tagged for recording observations. Planting was carried out during the last week of August 2025. Throughout the study period, uniform cultural practices were followed across all treatments. In each treatment, ten uniformly healthy plants were randomly selected for recording observations in each replication. The mean value for each parameter was calculated based on data recorded from selected plants Plant height of chilli was significantly influenced by both light spectrum and photoperiod under indoor growing conditions. Among the different light treatments, the combination of a higher proportion of blue light with an extended photoperiod (1R:2B + 16 hours of light) resulted in the greatest plant height at both observation stages, indicating its effectiveness in promoting vegetative growth. Treatments receiving a higher proportion of red light produced comparatively lower plant height, while the control treatment recorded the least growth. Among the two varieties, Thai chilli exhibited slightly greater plant height than Bullet chilli. Overall, the results suggest that a higher blue light proportion combined with a longer photoperiod is most effective for enhancing plant height in chilli under controlled environment conditions. Plant spread was significantly affected by the interaction of light spectrum and photoperiod in chilli grown under indoor conditions. Treatments with a higher proportion of red light promoted greater canopy expansion compared to treatments with a higher proportion of blue light and the control. Among all treatments, the combination of 2R:1B with a longer photoperiod produced the maximum plant spread, indicating that redenriched light coupled with extended light exposure enhances lateral growth and branching. The control treatment recorded the lowest plant spread throughout the growth period. Between the two varieties, Bullet chilli showed a slightly wider plant spread than Thai chilli. Overall, the results indicate that a red-dominant light spectrum combined with a longer photoperiod is most effective for improving plant spread in chilli under controlled environment cultivation.

Results and Discussion

Leaf area

Leaf area of chilli was significantly influenced by the interaction of light spectrum and photoperiod under indoor growing conditions. Treatments with a higher proportion of red light generally promoted greater leaf expansion compared to bluelight-dominant treatments and the control. Among all treatments, the combination of 2R:1B with a shorter photoperiod recorded the highest leaf area, indicating its effectiveness in enhancing leaf development and canopy growth. The control treatment exhibited comparatively lower leaf area, suggesting that optimized red and blue light combinations are more beneficial than white light alone. Between the two varieties, Bullet chilli produced a slightly larger leaf area than Thai chilli. Overall, the results indicate that a red-dominant light spectrum is more effective in promoting leaf area development in chilli under controlled environment conditions.

Number of days to flower intiation

The analysis of variance indicated that the treatments exerted a highly significant influence on the studied parameter, as evidenced by the significant F-value (36.634) at 1 per cent level of significance. Among the different treatments, Treatment 5 and Treatment 10 recorded the highest mean value (149.111), demonstrating their superiority over the remaining treatments.

Conclusion

Among the two chilli varieties evaluated, Bullet chilli exhibited superior overall performance, particularly with respect to reproductive and yield attributes. It recorded higher fruit number, fruit weight, and yield per plant compared to Thai chilli, indicating its better adaptability and productivity under controlled indoor growing conditions. Therefore, Bullet chilli can be considered the more suitable genotype for indoor vertical farming and speed-breeding applications. Regarding light treatments, the 1R:2B LED spectrum with a 14-hour photoperiod emerged as the most effective treatment for enhancing yield and fruit production, while the 1R:2B LED spectrum with a 16-hour photoperiod promoted maximum vegetative growth and chlorophyll accumulation. The findings demonstrate that blue-enriched LED lighting plays a critical role in improving plant growth, productivity, and quality traits of chilli under controlled environments. Hence, the combination of blue-dominant LED light and optimized photoperiod can be recommended for efficient indoor cultivation of chilli.

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