Season and Explant Origin Affect Phenolic Content, Browning of Explants, and Micropropagation of ×Malosorbus florentina (Zucc.) Browicz

The aim of this study was to develop an efficient protocol for in vitro propagation of the rare and endangered × Malosorbus florentina , not only enabling conservation of the species, but also its use as an ornamental. Explants excised from adult plants, shoot tip explants, and explants collected in March and April showed more browning and had higher content of total phenolics than explants excised from juvenile tissue, nodal explants, and those collected during any of the other months of the year. Shoot tip explants from adult plants were more difficult to establish in vitro (14%) compared with explants from micropropagated plantlets or sprouts of burned plants (29% to 36%). Nodal explants excised from seedlings were established at the highest percentage (83%), giving the most shoots per explant (5.2). Generally, in vitro cultures established from adult plants, with the exception of one culture, showed lower multiplication rates compared with cultures from juvenile plants. Nodal explants from the base of sprouts produced a higher percentage (60%) of shoots than explants from upper locations (20% to 31%), but any differences in proliferation rates of established cultures ceased after the third subculture. Microshoots from juvenile cultures were more capable of rooting (51% to 58%) than were those from adult plants (16% to 32%), whereas 83% of the plantlets were acclimatized ex vitro independently of their origin, but plantlets of juvenile origin, although developing the same height as those originating from adult plants, had shorter internodes and thus more compact shape.