Effect of LED lighting on the rooting of micropropagated raspberry (Rubus idaeus L.) plants

Light emitting diodes (LEDs) have become an alternative to fluorescent lamps for lighting plant tissue culture due to their low energy consumption, low heat emission, monochromatic spectra and long life. The aim of this study was to investigate the effects of LEDs on the rooting of in vitro cultivated raspberry ( Rubus idaeus L. 'Lloyd George') plants and their subsequent ex vitro acclimatization under sunlight in a greenhouse. The plantlets were cultivated in vitro under an illumination system based on Philips GreenPower LED research module. Four groups of LEDs emitting in white (W), red (R), blue (B), mixed (W:R:B:far-red = 1:1:1:1) spectral regions and fluorescent lamps (control) were used in our studies. Photosynthetic photon flux density (PPFD) of treatments was 87 +/- 7.5 mu mol m(-2) s(-1) for 16 h day(-1). Growth parameters, photosynthetic pigments content, net photosynthesis rate, transpiration, chlorophyll a fluorescence (OJIP testof the plantlets were measured after three weeks on rooting medium under the respective light regimes and three months after transplanting to the greenhouse under sunlight. The results indicated that the best rooting (88.22%) was obtained under mixed LED light. Plants cultivated under red LED light had the lowest percentage of rooting, fresh and dry biomass, but the longest shoots were reported. After acclimatization in the greenhouse, their biomass and leaf area did not differ significantly from the plants grown under white and mixed LED lights. Plants micropropagated and rooted under blue light, showed significantly slower growth and biomass accumulation and did not reach the size of plants from the other light treatments even after 90 days in sunlight in the greenhouse.