Supplemental lighting for greenhouse-grown strawberries: effects of different ratios of red to blue radiation

Innovative plant lighting technologies based on light-emitting diodes (LEDs) are developed for various crops today. The ability to tailor the light spectrum for the desirable plant responses appears to be one of the advantages in these light sources. On the other hand, LED application requires fine light environment tuning according to the crop/cultivar demands. We studied strawberry (Fragaria × ananassa) plant responses to cultivation in the greenhouse under natural light with supplementary lighting. For artificial lighting, narrow-band LED light sources were used with various ratios of red to blue radiation (2:1 and 8:1), PPF 180 µmol m^-2 s^-1; high pressure sodium (HPS) lamps were used as reference light sources, PPF 300 µmol m^-2 s^-1. Five new cultivars of strawberry were studied in the greenhouse from October to April: 'Bohemia', 'Vechnaya vesna', 'Govorovskaya', 'Rannyaya plotnaya', and 'Snezhana'. Light quality influenced plant growth, development, and chemical composition of the fruits. HPS lighting accelerated plant development by 2-3 weeks. Preliminary results indicate various growth and development responses between the cultivars to LED lighting with different ratio of red to blue. With 'Bohemia' plants, HPS lamp lighting increased yield by 3.6 and 6.7 times compared with LED (R:B=2:1) and LED (R:B=8:1), respectively; while with 'Snezhana' the yield under LED (R:B=2:1) was two times higher. With the 'Govorovskaya' and 'Rannyaya plotnaya' cultivars, the highest productivity was observed with LED lighting (R:B=8:1). The highest sugar accumulation in the fruits was under HPS lighting in all cultivars studied, except 'Vechnaya vesna'.