Tomato Fruit Growth and Nutrient Accumulation in Response to Blue and Red Light Treatments during the Reproductive Growth Stage

Tomatoes are an important fruit consumed worldwide. Within protected cultivation environments, artificial light using energy-efficient light-emitting diodes can be applied in tomato production as an effective way to improve productivity and nutritional value. Several studies have investigated the effects of supplementing artificial light on various aspects of tomato growth, encompassing flowering, fruit development, ripening, and nutritional composition. However, the outcomes of previous studies offer inconclusive insights into whether the observed impacts on tomato growth have resulted from the provision of additional photons or discrepancies in the spectral distribution of light during artificial light supplementation. Within this context, this study aimed to specifically explore the independent effects of monochromatic blue and red light, along with their dichromatic mixture (blue + red), on fruit growth and nutrient accumulation in comparison with multispectral white light. These four different light treatments were implemented after anthesis under the same photosynthetic photon flux density to mitigate possible variabilities arising from different light intensities and originating during the vegetative growth stage. As a result, under the same light intensity conditions, red and blue + red light irradiance during the reproductive growth stage delayed fruit ripening by up to 4.33 days compared to white light. Regarding fruit productivity, the fresh weight of fully ripe tomato fruit in the blue, red, or blue + red light treatment groups was not different from that in the white-light treatment group, whereas the blue light treatment significantly reduced the number of fruits in the plant. Finally, nutrient content, including soluble sugars, lycopene, and beta-carotene, significantly increased by 10.0%, 27.1%, and 65.2%, respectively, in the blue compared to the white light-irradiated group. This study demonstrated that the application of distinct light spectra during the reproductive growth phase could have varying impacts on tomato fruit development and nutrient accumulation. By integrating our findings with results from prior studies, a more efficient light intervention strategy could be developed to effectively regulate traits of tomato fruit within an indoor production system.