Improving the efficiency of maturation and conversion of tamarillo somatic embryos

Somatic embryogenesis is a process that allows the fast propagation of economical important species and a powerful tool in breeding and genetic transformation. One of the most critical phases in this process is the embryo maturation, since during this stage it is usual to find a significant number of anomalous embryos, limiting their conversion into emblings. Somatic embryogenesis induction and somatic embryo development of the tamarillo tree (Cyphomandra betacea) have been studied at our laboratory and successfully used on the regeneration of this solanaceous species from several types of explants. It is a two-step system in which somatic embryogenesis is induced in MS medium containing an auxin and high sucrose concentrations and the embryogenic tissues obtained must be transferred to an auxin-free medium with lower sucrose levels in order to obtain somatic embryos. Previous work has shown that by optimizing maturation conditions a higher yield and a better quality of the formed embryos can be achieved and even though a high number of anomalous embryos were still formed, plant conversion was not significantly affected, indicating that shoot apical meristem development was not always affected in anomalous somatic embryos. In this work, we intended to optimize tamarillo’s somatic embryo maturation and conversion by testing different types of embryogenic calli under several conditions of maturation. Calli with different ages and origins were evaluated, ranging the culture medium composition, particularly by the addition of activated charcoal, different osmotic agents, oxidative agents and abscisic acid. The monitoring of the maturation and conversion processes by histological analysis allowed us to closely observe the effects of the culture conditions on embryo development, namely on the apical-basal pattern and SAM organization, which can be related to the ability of the embryo to develop into a normal plant.