Suplementação luminosa com LED em petúnia: respostas fisiológicas, produtividade e qualidade

Abstract

Light supplementation (LS) can play a crucial role in the cultivation of ornamental plants, directly influencing their development and quality. The use of artificial light sources, such as LEDs, allows precise adjustment of spectral quality and light intensity according to the specific needs of the plant throughout its life cycle. In the city of Pelotas, located in the extreme south of Brazil, there are still no records of studies using LS in the production of petunia, which is one of the main ornamental plants cultivated in this region. In this context, this study aims to evaluate the effects of different LS sources using LEDs on the growth, morphology, production and quality of petunias grown in an agricultural greenhouse. Two experiments, using three different LS sources, were carried out for the cultivation of two varieties of Petunia x hybrida (Miliflora, color „White‟ and Pendula, color „Red‟). In the first experiment, LED tube lamps were used with two combinations of blue (B) and red (R) light, in the proportions: 85%B+15%R and 15%B+85%R, and white (W) light 100%, with a light intensity of 25 (±5) μmol m-2 s-1, in addition to the condition without artificial lighting (control). In the second experiment, LED panels were used with the combination of red (R), blue (B) and white (W) light, in the proportions: 73%R+27%B, 73%W+27%R and 100%W, with a light intensity of 150 (±10) μmol m-2 s-1, in addition to the control. In both experiments, the cultivation cycle comprised the three phases of plant commercialization: production of plugs, seedlings and adult plants. In the „plugs‟ phase, biometric evaluations were carried out, while in the seedling and adult plant phases, in addition to these, analyses were carried out on pigments and photosynthetic parameters. In general, the biometric variables were: height of the aerial part, number of leaves, leaf area, dry mass of the aerial part, dry mass of branches, dry mass of flowers and flower buds, dry mass of roots, aerial part-root ratio, total dry mass of the plant, number of branches, number of flower buds and open flowers per plant; in addition to the analysis of pigments: chlorophyll indices, flavonoids, anthocyanins, nitrogen balance, accumulation of chlorophylls a and b, carotenoids, chlorophyll fluorescence; and photosynthetic parameters: net photosynthetic rate, stomatal conductance, internal carbon concentration and transpiration rate. Overall, the results indicate that light supplementation with LEDs should be adapted to the characteristics of each petunia variety and its growth stage. The combination of red and blue LEDs proved to be superior in terms of photosynthesis, although the low light intensity limited growth. The combination of white and red light shows promising potential to accelerate development and flowering, suggesting that other cultivars may also benefit from similar strategies. On the other hand, the use of white LEDs may be more economically viable and offer better visual quality for the production of adult plants. Thus, the choice of different combinations of LEDs can optimize plant growth and quality, resulting in more efficient and market-attractive production.