Plant regeneration of Oncidium varicosum (Orchidaceae) by means of root tip culture.

The effects of an auxin (NAA) and a cyto kinin (BA), as well as those of peptone, thiamin and coconut water (CW) on callus and protocorm-like body (PLB) induction from root tips of Oncidium varicosum grown in vitro were studied. Relatively high concentrations of NAA favoured callus induction. PLBs were obtained from callus culture either in medium with 15% CW+1.25 mg/1 NAA or in the presence of CW alone. The low regeneration capac ity of buds presented by the calli seems to be the result of an incomplete dedifferentiation of their cells. This seems to keep the callus in a "root state". The apparent presence of high cytokinin levels either in the explant or in the callus may be related to these processes.