Species-dependent divergent responses to in vitro somatic embryo induction in Passiflora spp.

Abstract

Passiflora is a large and widespread genus of tropical plants that includes over 500 species. Organogenesis-based in vitro plant regeneration systems have long been available for the commercially important species Passiflora edulis, the passionfruit, and for a few other related wild species. Recently, somatic embryogenesis from mature zygotic embryos was reported for passionfruit and for a related wild species, P. cincinnata, although the recovery of entire plants was obtained only for the latter. Here we assessed the in vitro morphogenic responses of zygotic embryos of five different Passiflora species (P. alata Curtis, P. crenata Feuillet & Cremers, P. edulis Sims, P. foetida L. and P. gibertii N.E. Brown) cultured in basal Murashige and Skoog (MS) medium supplemented with 4.5 μM 6-benzyladenine (BA) and different concentrations (13.6, 18.1, 22.6 or 27.1 μM) of 2,4-dichlorophenoxyacetic acid (2,4-D). We characterized these different responses using light and scanning electron microscopy. Somatic embryos were obtained in MS medium supplemented with 4.5 μM BA and either 13.6 or 18.1 μM 2,4-D for all species, except P. foetida for which only indirect shoot organogenesis was observed. Regeneration of entire plants that could be acclimatized was achieved for all species studied. Additionally, our results indicated that the in vitro conditions that promote somatic embryogenesis in some Passiflora species might induce shoot organogenesis in others, suggesting that the conservation of morphogenetic signals among Passiflora species might be limited by their phylogenetic relatedness.