Photoautotrophic culture of Coffea arabusta somatic embryos: development of a bioreactor for large-scale plantlet conversion from cotyledonary embryos

Somatic embryos were developed from in vitro-grown leaf discs of Coffea arabusta in modified Murashige and Skoog medium under 30 micromol 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 micromol 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.