Blue Light Enhances Flowering and Functional Properties of Purple Viola for Improved Edible Flower Production

The increasing demand for edible flowers exhibiting both visual appeal and functional properties has prompted scholarly interest in light-based strategies to enhance their quality. This study investigated the impact of blue light duration on morphological traits, antioxidant activity, and phytochemical accumulation in two Viola cultivars with varying petal sizes. Plants were cultivated under a 12-hour daily photoperiod, during which the irradiation time of white (W) and blue (B) LEDs was varied among treatments (W12+B0, W8+B4, W4+B8, W0+B12), while maintaining constant total light intensity. The results indicated that prolonged B light exposure significantly elevated plant height and flowering rate, particularly in the smaller-petaled cultivar ‘Delta Beaconsfield’ (DB), while also promoting anthocyanin synthesis and ABTS-based antioxidant activity. Conversely, the cultivar ‘Delta Trueblue’ (DT) demonstrated higher total phenolic and flavonoid contents under mixed W+B illumination and exhibited a more robust DPPH radical scavenging capacity. Notably, DB maintained elevated chlorophyll levels even under monochromatic B light, suggesting a distinctive photoadaptive or light-harvesting mechanism. The differential responses observed between cultivars and assays reflect variations in the light-regulated synthesis of hydrophilic and lipophilic antioxidants. These findings underscore the potential of spectral manipulation, particularly through blue light, to enhance the functional quality of edible Viola flowers.