Evaluation of Growth, Flowering, and Chlorophyll Fluorescence Responses of <italic>Viola cornuta</italic> cv. Penny Red Wing according to Spectral Power Distributions

Abstract

Background and objective: The genus <i>Viola</i>, a member of the Violaceae family, is renowned for its ornamental flower crops. Additionally, <i>Viola</i> species are relatively pest-resistant and easy to manage. They are widely used in gardens, and some of their flowers are even edible. In this study, our focus was on <i>V. cornuta</i> cv. Penny Red Wing (hereinafter referred to as ‘Penny Red Wing’), an experimental plant chosen for its high ornamental value and rapid growth.Methods: We applied a purple light-emitting diode (LED) and three types of white LEDs with varying color temperatures: 3000, 4100, and 6500 K, respectively, as artificial light sources. Notably, a purple LED has a far-red wavelength (700-800 nm) ratio of approximately 17.6% in their spectral power distribution.Results: The findings indicated that several parameters exhibited higher values under purple LED: shoot size parameters, shoot biomass, moisture content of shoots and roots, photochemical reflectance index (PRI), modified chlorophyll absorption ratio index (MCARI), total number of flowers, flower size parameters, scent score, F<sub>v</sub>/F<sub>m</sub>, and PI<sub>ABS</sub>. However, the 6500 K white LED led to higher evaluations of root length, number of shoots and leaves, root biomass, moisture content of shoots and roots, F<sub>v</sub>/F<sub>m</sub>, and PI<sub>ABS</sub>. Nevertheless, it was observed that shoot growth was relatively hindered, and the flowering responses were inadequate under the 6500 K white LED, suggesting their unsuitability for the mass production of ‘Penny Red Wing’. Furthermore, the 3000 and 4100 K white LEDs were also deemed unsuitable for cultivating ‘Penny Red Wing’ due to their lower cultivation efficiency.Conclusion: ‘Penny Red Wing’ was evaluated as having superior growth, flowering, and chlorophyll fluorescence responses under purple LED, indicating that the far-red wavelength had a more pronounced effect compared to the green wavelength (500-600 nm). Therefore, we recommend cultivating this cultivar under purple LED, which include the far-red wavelength.