Alternative induction of de novo shoot organogenesis or somatic embryogenesis from in vitro cultures of mature zygotic embryos of passion fruit ( Passiflora edulis Sims) is modulated by the ratio between auxin and cytokinin in the medium

Several reports on tissue culture-based techniques have been published for passion fruit ( Passiflora edulis ), an important tropical fruit crop. However, a system in which de novo shoot organogenesis (DNSO) or somatic embryogenesis (SE) can be induced from the same type of explant was not available so far. The present study describes an in vitro system that enables alternative induction of both morphogenetic pathways from P. edulis mature zygotic embryo. DNSO was observed when explants were cultured on Murashige and Skoog medium supplemented with high 6-benzyladenine (BA) to 2,4-dichloro-phenoxyacetic acid (2,4-D) ratios, such as 72.4 μM BA and 4.5 μM 2,4-D. Embryogenic calli were observed when low BA/2,4-D ratios, such as 4.5 μM BA and 72.4 μM 2,4-D were used. Morpho-anatomical characterization revealed that epidermal and sub-epidermal cells were involved with the regeneration process via both DNSO and SE pathways. These cells became meristematic and divided extensively to form protuberances after 12–15 days of culture in both systems. These protuberances led to the formation of either meristemoids or pro-embryogenic cell clusters, which differentiated into shoot buds or somatic embryos, respectively. The use of this system coupled with techniques that allow gene expression studies might greatly contribute to further studies on in vitro morphogenesis in Passiflora .