Mass propagation of coffee transplants under scaled-up photoautotrophic micropropagation system

Somatic embryos were obtained from leaf discs of coffee plants cultured in vitro. The main objective of our study was to develop a scaled-up micropropagation system under photoautotrophic conditions (PA) using Coffea arabusta somatic embryos as a model plant. At different developmental stages of somatic embryos (torpedo, precotyledonary, cotyledonary and germinated), the physiological variables in relation to the photosynthetic ability were investigated. Results revealed that cotyledonary and germinated stage embryos were physiologically capable to grow photoautotrophically. However, high photosynthetic photon flux (PPF: 100 mu mol m(2) s(-1)) treatment for 14 days increased the photosynthetic efficiency of the somatic embryos and possibly make them more suitable to grow under PA conditions. To confirm these findings the somatic embryos were cultured under PA conditions (sugar-free medium with CO2 enrichment in the culture vessel environment and high PPF). From the results it was concluded that cotyledonary stage is the earliest stage somatic embryo, which can be successfully grown photoautotrophically for conversion into plantlets. To scale up the plantlet conversion process of coffee somatic embryos under PA conditions a bioreactor was especially designed. The growth and conversion percentage of cotyledonary stage embryos cultured in the newly developed bioreactor were compared with those of commercially available systems such as RITA temporary immersion bioreactor and Magenta box. Results revealed that the growth, percent conversion and ex vitro survival of plants were highest in the newly developed bioreactor.