The Paradox cl. 'Vlach' multiplication and rooting rates are strongly affected by the explant position on the in vitro growing shoots

The multiplication and rooting rates achieved from in vitro cultured explants of Paradox cl. 'Vlach', proved to be highly affected by their position in the original shoot. Explants taken until the 3^rd internode below the apical meristem, when systematically subcultured each 30^th days, lost their multiplication capacity on each subculture, their regeneration efficiency becoming almost null after 5 subcultures. On the other hand, those taken below the 3^rd internode, reached an average of 5.5 new explants after the same time and no significant differences were registered between the 1^st and the 5^th subcultures. Concerning rooting capacity, cuttings prepared from the apical nodes of the in vitro growing shoot, presented a rooting potential of 75%, while those prepared from the basal part, never reached rooting rates higher than 49%. The results demonstrate that the correct choice of the explant, on each in vitro culture step, is determinant for the success of the technique.