Development of photoautotrophy in <i>Coffea</i> somatic embryos enables mass production of clonal transplants

Somatic embryogenesis offers the promise of a cost-effective, large-scale propagation method and is considered as a unique alternative technique to overcome some of the limitations of conventional clonal propagation methods. Production of somatic embryos from cell, tissue and organ cultures may occur directly which involves the formation of an asexual embryo from a single cell or a group of cells on a part of the explant tissue without an intervening callus phase. In this study, the photosynthetic ability of different stage coffee (Coffea arabusta) somatic embryos and the development of photoautotrophy are reported. Results revealed that cotyledonary and converted somatic embryos have the ability to photosynthesise and can be grown under photoautotrophic conditions (with no supply of sugar from the culture medium). The development of photosynthetic ability can be accelerated by placing the somatic embryos in a photosynthetic photon flux of 100 µmol m−2s−1 for at least 14 days. Cotyledonary stage somatic embryos were cultured under photoautotrophic conditions in three different growing systems to develop an optimized protocol for a large-scale embryo-to-plantlet conversion and propagation system. Our results demonstrated that the use of a newly developed temporary root zone immersion bioreactor is effective for the embryo-to-plantlet conversion and enhanced growth under photoautotrophic conditions.