Efficient production of virus-free apple plantlets using the temporary immersion bioreactor system

Viral pathogens reduce the quality and yield of apple (Malus domestica) fruits by 30-50%. A mass production system of virus-free apple plantlets is needed to meet the demand of the domestic fruit tree industry. In this study, we compared the production of virus-free plants in different in vitro culture systems, including a temporary immersion bioreactor (TIB), a continuous immersion bioreactor, and conventional solid and liquid culture systems (controls). Apple plantlets were immersed in the TIB once every 3 h (TIB-3) or 6 h (TIB-6). The fresh weight of apple plants was the highest in the TIB-3 system and lowest in the liquid culture. Shoots were the longest in the TIB-3 system, approximately twofold longer than those in solid culture and liquid culture. Roots of apple plants were the longest in the TIB-3 system compared with solid and liquid cultures. Root number in the TIB-3 system was also higher than that in solid and liquid cultures. Moreover, leaf area was the highest in plants grown in the TIB-3 treatment. The total stem area of TIB-3 plants was the largest at 1.46 mm(2). This study suggests that the airlift bioreactor is capable of producing a large number of virus-free plants in a short time compared with conventional culture systems. Additionally, secondary xylem was well developed in the stems of plants grown in the TIB-3 system. Therefore, this system shows a high potential for producing healthy plants suitable for acclimatization.