The aim of this work was to optimize in vitro storage of yacon (Smallanthus sonchifolius) under slow-growth conditions. Mediumterm conservation was tested on ½ MS supplemented with mannitol and sorbitol (1-3%), BAP (5 mg l-1), or MS and ½ MS medium free of plant growth regulators. Within 60 days, height of plants, number of nodes, number of roots and their length were measured in all of these treatments. The results revealed that there was a decline in plant growth along with the increase in the concentrations of mannitol (1.88, 1.49 and 1.07 cm for 10, 20 and 30 g l-1 mannitol) and sorbitol (3.66, 3.19 and 1.74 cm for 10, 20 and 30 g l-1 sorbitol), and along with the decrease of nutrient concentration in the cultivation medium (4.74 and 2.24 cm for MS and ½ MS medium). The survival of explants was found to be minimal at the highest concentrations of osmotic regulators (70% in mannitol and 50% in sorbitol) and on the medium supplemented with BAP (60%), while maximal on MS medium, ½ MS medium and on ½ MS medium with addition of 10 g l-1 mannitol (in all cases 100%). On full-strength MS medium and medium with addition of BAP plant growth was rapid, suggesting that these media could be rather used for multiplication of yacon. On the basis of our results it can be concluded, that for medium-term conservation of yacon can be satisfactory used ½ MS medium and media supplemented by 10 or 20 g l-1 mannitol or sorbitol.
