Influence of source and concentration of carbohydrate on shoot growth and rooting of Oncidium varicosum Lindl. (Orchidaceae)

Abstract

Oncidium varicosum is a native Brazilian orchid popularly known as 'Golden Shower' because of its very ramified inflorescence and many yellow flowers. The carboydrate type and concentration are important in promoting plantlet development of in vitro orchids. The present study was carried out to asses the effect of different carbohydrate sources and concentrations on the in vitro growth of O. varicosum plantlets. Murashige e Skoog culture medium was used modified with half concentration of the macronutrients. The plantlets, derived from seeds that were already established in vitro and 0.8 + 0.2 cm in height, were inoculated in the culture media containing the following carbohydrate sources: saccharine, maltose and glucose, at concentrations of 0, 10, 20, 30, 60 and 90 g.L-1. The following variables were analyzed 8 months later: canopy height, number of roots, greatest root length, pseudobulb diameter and fresh weight. A completely randomized block experimental design was used with five replications per treatment. Analysis of variance and the Tukey test (5%) were performed to compare the means. It was concluded that 60 g.L-1 saccharose was the best treatment for all the parameters assessed. The sugars 30 g.L-1 glucose and 60 g.L-1 maltose were also suitable, but presented lower pseudobulb diameter and lower fresh weight when compared to 60 g.L-1saccharose.