In the present study, ex vitro 4-month shoots grown under different light conditions in the previous experiment were used as initial explants for regeneration. After sterilization, the shoots were cut into single nodes and these nodes then were cultured into culture vessels. After 45 days of culture, the results indicated that the young shoots grown under different light conditions gave a significantly higher regeneration rate compared with the control except shoots placed under 50R:50B. Interestingly, what is surprising in the current study is that lower contamination rates were recorded (37.50–52.50 %) when compared with previous studies. Plants exposed to 100R and 90R:10B revealed significantly higher regeneration and lower contamination rates compared to the control (Fig. 2). It might be explained that under these conditions the stem elongation was better than the control, and single nodes were obtained. These nodes then were effectively surface sterilized. In contrast, the shoots grown under 50R:50B and the control resulted in the
same regeneration rate—at low level—18.75 % together with a high contamination rate of 52.50 % (Fig. 2). Although the shoots grown in the darkness were found to give a significant stem node elongation, the low survival rate of 10.00 % was recorded. In this experiment, the shoots grown under 100B gave the highest regeneration rate (33.50 %) (Fig. 4g). According to Tibbitts et al. (1983), blue light is important in chlorophyll biosynthesis, stomata opening, enzyme synthesis, maturation of chloroplasts and photosynthesis. The blue light is also indispensable for the morphologically healthy plant growth (Giedre et al. 2010). Therefore, shoots were pre-treated under 100B might have a higher vitality comparing to the others.