Effects of Supplemental Lighting with High-Pressure Sodium or Plasma Lamps on Quality and Yield of Cut Roses

Abstract

Used as supplemental lighting (SL) in protected flower growing systems, newly developed sulfur plasma lamps (PLS) may confer benefits in terms of growth, yield, and quality. This study compared the effects of SL with PLS versus conventional high-pressure sodium lamps (HPS) on the growth characteristics, yield, and quality of cut roses cultivated in winter. Between October 10, 2016 and March 23, 2017, standard cut rose (Rosa hybrida) cultivars ‘Aqua’ and ‘Brut’ were grown under PLS and HPS with a photosynthetic photon flux density (PPFD) of 120 μmol·m -2 ·s -1 for 14 hours (between 17:00 and 07:00). Rose plants were cultivated in a plastic greenhouse in Gyeongsan, Gyeongsangbuk-do. A control condition used HPS with PPFD at 10 μmol·m -2 ·s -1 to offset the effect of the photoperiod. Cut flowers were harvested twice a week from December to March, and their growth and flowering characteristics, yield and quality of cut flowers were measured at each harvest. PLS had more blue (B) light and less red (R) light and near-infrared light than HPS; green and far-red light (FR) levels were similar. Plants under SL with PLS therefore received a higher B:R ratio and lower R:FR ratio than those under HPS. SL with PLS and HPS improved almost all of the characteristics of ‘Aqua’ and ‘Brut’ compared with the control. In particular, SL with PLS in ‘Aqua’ increased cut flower length, fresh and dry weights, vase life, and the number of higher grade products than SL with HPS. These differences could be associated with the relatively low R:FR ratio of PLS, which may have increased stem length and leaf area, thus increasing photosynthesis and resulting in higher yield and quality of cut flowers, as well as a shorter crop period. Likewise, the relatively high B:R ratio of PLS may have promoted gas exchange through stomatal opening and increased photosynthesis, resulting in higher yield and quality. However, the effect of light source for SL on morphological characteristics such as leaf area and stem length may be somewhat cultivar-dependent because the effect of SL with PLS in ‘Brut’ was smaller than that in ‘Aqua’.