Photoautotrophic Culture of Coffea arabusta Somatic Embryos: Development of a Bioreactor for Large‐scale Plantlet Conversion from Cotyledonary Embryos

摘要

Somatic embryos were developed from in vitro‐grown leaf discs of Coffea arabusta in modified Murashige and Skoog medium under 30 µmol m^–2 s^–1 photosynthetic photon flux (PPF). Cotyledonary stage embryos were selected from the 14‐week‐old cultures and were placed under a high (100 µmol m^–2 s^–1) PPF for 14 d. These pretreated embryos were grown photoautotrophically in three different types of culture systems: Magenta vessel; RITA‐bioreactor (modified to improve air exchange); and a specially designed temporary root zone immersion bioreactor system (TRI‐bioreactor) with forced ventilation. The aims of the study were to achieve large‐scale embryo‐to‐plantlet conversion, and to optimize growth of plantlets under photoautotrophic conditions. The plantlet conversion percentage was highest (84 %) in the TRI‐bioreactor and lowest in the modified RITA‐bioreactor (20 %). Growth and survival of converted plantlets following 45 d of photoautotrophic culture in each of the three culture systems were studied. Fresh and dry masses of leaves and roots of plantlets developed in the TRI‐bioreactor were significantly greater than those of plantlets developed in the modified RITA‐bioreactor or Magenta vessel. The net photosynthetic rate, chlorophyll fluorescence and chlorophyll contents were also highest in plantlets grown in the TRI‐bioreactor. Normal stomata were observed in leaves of plantlets grown in the TRI‐bioreactor, whereas they could be abnormal in plantlets from the modified RITA‐bioreactor. Survival of the plants after transfer from culture followed a similar pattern and was highest in the group grown in the TRI‐bioreactor, followed by plants grown in the modified RITA‐bioreactor and Magenta vessel. In addition, ex vitro growth of plants transferred from the TRI‐bioreactor was faster than that of plants from the other culture systems.