Protocorm-like body induction and subsequent plant regeneration from root tip cultures of Doritaenopsis

The effect of cytokinins thidiazuron (TDZ), benzyladenine or zeatin on protocorm-like body (PLB) induction from root tips of Doritaenopsis grown in vitro was studied. Among the cytokinins tested, TDZ was found to be more effective cytokinin in the induction of PLBs than benzyladenine (BA) or zeatin. On modified Murashige and Skoog medium (MS) supplemented with 2.3 muM TDZ the highest percentage of PLB formation (47.2%) occurred and each explant produced two to six PLBs. Histological observations indicated the existence of two kinds of pathways during PLB formation: direct PLB induction from the root meristem and callus-mediated PLB induction from cortical cells. During callus-mediated PLB regeneration, the initial cell divisions occurred in the cortex region of root apices followed by accumulation of callus like masses in the cortex region. These cell masses developed globular structures that developed into PLBs after 5 weeks of culture. Upon subculturing to a modified Hyponex medium, PLBs developed into plantlets that were successfully acclimatized in green house conditions. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.