Effect of primary culture medium composition on high frequency somatic embryogenesis in different Coffea species

High frequency somatic embryogenesis can be obtained over a 7-8 month culture period when using current routing coffee tree micropropagation protocols. To reduce this response time and improve the embryo formation yield, eight different media were tested for primary culture. These media differed from the classically used ones by their mineral nitrogen and plant growth regulator concentrations. An increase from 0.66 to 0.75 in the NO3/NO3+NH4 ratio and a 2-fold lower plant growth regulator concentration in the primary culture medium led to substantial improvements in terms of rapidity and embryo/plantlet regeneration frequencies. Embryo development time was reduced by up to 3 months with a 5-fold increase in the number of formed embryos. These results were obtained for the two cultivated coffee tree species, Coffea canephora and C. arabica, and for a wild one, C. heterocalyx, but not for a second wild species, C. sp. Moloundou showing a species-specific response. The new conditions described in this paper led to a substantial enhancement that should be particularly helpful for clonal propagation and genetic engineering of cultivated coffee plants.