Series of three different experiments were carried out, in order to study the optimization of the use of bulblets obtained in vitro, in the micropropagation of the onion (Allium cepa L.). Initially, it was evaluated the effects of the interaction between two doais of 6-benzylaminopurine (BAP) and naphthaleneacetic acid (NAA), and the position of the explant in the medium, for the cultivara Pira Ouro and Pirana Precoce. For 'Pira Ouro' the phytohormone concentrations did not affect the percentage of regeneration; however, for 'Pirana Precoce', the rates of 4.0 mg/L of BAP and 0.5 mg/L of NAA gave the best results. The highest multiplication rate, measured by the number of shoots obtained, for both cultivars, was observed with 2.0 mg/L of BAP and 0.25 mg/L of NAA. The vertical position of the explant showed a tendency of increasing the percentage of regeneration for the two genotypes. Explants from bulblets obtained with the sucrose concentration of 120 g/L were best fitted for the regeneration process, as showed by the second experiment, carried out with the Pira Ouro cultivar and the hybrid Pira Ouro x Pirana Precoce. The size of the bulblet, measured as its diameter, utilized as the source of the explants was studied in the third one, for the same cultivars utilized in the first experiment. For 'Pira Ouro', there was no influente, both, for the percentage of regeneration and the number of shoots obtained. The small diameter (P: < 5 mm) and the medium one (M: 5 a 10 mm), in the Pirana cultivar, had higher percentage of regeneration; the highest number of shoots was obtained with M diameter.
onion; Allium cepa L.; tissues culture; micropropagation