Shoot proliferation and in vitro organogenesis from shoot apex and cotyledonary explants of royal poinciana (Delonix regia), an ornamental leguminous tree

Key message Cytokinin supplementation was essential for the induction of shoot proliferation and in vitro organogenesis from shoot apices and cotyledons of D. regia, respectively. Micropropagation techniques have been established for woody species to facilitate their mass clonal propagation and to better understand their processes of regeneration. The goal of this work was to evaluate the potential of shoot apex and cotyledonary explants of Delonix regia, commonly known as royal poinciana, to be induced to undergo shoot proliferation and in vitro organogenesis, respectively. Shoot apices and cotyledons obtained from in vitro-germinated seedlings were inoculated onto Murashige and Skoog (MS) medium supplemented with different concentrations (0.125, 0.250, 0.5, 1.0 and 2.0 mg L-1) of 6-benzyladenine (BA) and a control without BA. After 30 days of cultivation, multiple shoot formation and adventitious shoots were observed in shoot apices and cotyledonary segments of D. regia, respectively. Both explant sources exhibited a dose-dependent behavior with increased fresh mass and shoot number with increasing BA concentrations. The greatest number of shoots was observed in explants cultured on BA-supplemented (2.0 mg L-1) medium; however, the leaflets of shoots grown in MS medium with higher BA concentrations were smaller. Histological analysis revealed that the formation of adventitious shoots occurred through the reprogramming of mesophyll cells in the edge regions of the cotyledonary explants. The results obtained here provide new information for optimizing and establishing efficient regeneration systems and micropropagation of royal poinciana, an important ornamental tree species.