Comparative ontogenesis of Coffea arabica L. somatic embryos reveals the efficiency of regeneration modulated by the explant source and the embryogenesis pathway

Abstract

In vitro micropropagation is an important technique for coffee multiplication performed by somatic embryogenesis, which can be indirect, with the formation of calluses, or direct, when embryos are formed directly from explant cells. In the present study, we characterized the ontogenesis of somatic embryos regenerated via indirect and direct somatic embryogenesis in leaf explants from Coffea arabica ‘Mundo Novo’ and assessed the development of these embryos in leaf explants from adult plants maintained ex situ and in vitro. Anatomical analyses showed that leaf explants present structural differences depending on their origin. In the direct pathway, tissue develops more rapidly in explants from in vitro plants than in those from ex situ explants. In both methods, the formation of a pro-embryogenic mass was found to be essential for embryo formation. In the indirect pathway, calluses from ex situ material presented elongated cells and a loose external appearance. Conversely, calluses from in vitro material presented large regions of meristematic cells with a single large nucleus and dense cytoplasm. We propose that indirect somatic embryogenesis in in vitro–grown explants may accelerate genetic breeding in coffee, and it represents the most efficient condition for somatic embryogenesis, producing embryos in less time than the required by ex situ plants (indirect: 260 d in ex situ conditions, 62 d in vitro; direct: 270 d ex situ, 86 d in vitro).