EFFECTS OF KINETIN, PACLOBUTRAZOL AND THEIR INTERACTIONS ON THE MICROTUBERIZATION OF POTATO STEM SEGMENTS CULTURED INVITRO IN THE LIGHT

Single-nodal cuttings of Solanum tuberosum (four cultivars) and Solanum chacoense were induced to produce in vitro microtubers on Murashige & Skoog (MS) medium supplemented with 8 g l-1 sucrose and various concentrations of kinetin and paclobutrazol. The cultures were kept 10 days in darkness and then transferred to a 14 h daylength with 100 muE m-2 sec-1 light intensity at 21-degrees-C. Kinetin (2.5 mg l-1) had no significant influence on tuber formation. However, its addition together with paclobutrazol (0.001 mg l-1) significantly enhanced tuberization. Paclobutrazol alone stimulated early tuber initiation and inhibited stem growth. Despite some genotype x treatment interactions, all genotypes (from very early to late and wild type) formed the maximum proportion of explants bearing microtubers on the media containing both plant growth regulators.