Poor germination of Stevia rebaudia

Poor germination of Stevia rebaudiana Bertoni seeds is a phenomenon with unknown reason and the research concerning the improving of germination are still in progress. We investigated the influence of light-emitting diodes (LEDs) spectra on Stevia seed germination as well as seedling growth and selected morphological and biochemical parameters. Blue LED light increased seed germination and affected the development of the largest number of leaves and roots in 4-week-old Stevia plantlets. It has also the most favourable effect on the number and opening of stomata. Red LED light however, significantly increased the length of stems and roots, although there was not correlation with the fresh weight (FW). The highest FW of Stevia plantlets achieves under combined red and white LED light at temperature of 20 degrees C as well as under white fluorescent light at temperature of 25 degrees C. Blue LED light also positively affected the carotenoids concentration, whilst the highest concentration of chlorophyll a and b was found, in plantlets grown under white fluorescent light. The less favourable effect on the synthesis of all the examined pigments was exerted by red LED light. The largest amounts of phenolics and soluble sugars accumulated plantlets growing in the darkness and irradiated blue LED light. In addition, all LEDs affected the activity of antioxidant enzymes. The blue LED light increased the activity of catalase (CAT) and peroxidase (POD), especially at 25 degrees C. Red LED light significantly increased activity of superoxide dismutase (SOD) whilst for the activity of CAT and POD opposite effect was observed. The combined red with white LED light was the most favourable for the activity of CAT at 25 degrees C. We conclude that the seed germination and the quality of Stevia plantlets could be improved by controlling light quality. (C) 2016 Elsevier B.V. All rights reserved.