Plant growth, tuber yield formation and costs of three different propagation methods of yacon (Smallanthus sonchifolius)

Yacon (Smallanthus sonchifolius) ((Poepp. and Endl.) H. Robinson) is a perennial plant native to the Andean region. Its tubers contain high amounts of fructooligosaccharide and inulin (up to 60% of DM) which are supposed to have positive effects on human health. One major aspect currently limiting yacon cultivation is the high cost of propagation. The aim of the present study was to investigate three different propagation methods i) divided seedling after budding from mother plants with pre-cultivation in the greenhouse (DSAB), ii) seedlings from rhizome pieces pre-cultivated in the greenhouse (RP1), and iii) rhizome pieces directly planted into the field (RP2) in regard to plant growth, tuber yield formation and costs. The propagation methods DSAB (92 cm) and RP2 (85 cm) produced significant bigger plants than RP1 (70 cm). Leaves and ramifications showed a similar trend, additionally number of ramifications of DSAB (24) differed significantly to RP1 (16) but not to RP2 (18). The average rhizome weight at harvest was highest for DSAB with 871 g and lowest for RP1 with 561 g. Contrary to that, on a hectare basis RP1 achieved highest tuber yields (29.8 t FM ha−1). The tuber yields of DSAB and RP2 were considerably lower with 21.3 and 17.8 t FM ha−1 respectively. Mean fresh weight of tubers differed significantly between RP1 (308 g) and RP2 (196 g), whereas DSAB (255 g) did not differ significantly from RP1 or RP2. Furthermore, RP1 reached the highest number of tubers per plant (8.2) compared with DSAB (5.6) and RP2 (6.6).Due to the highest tuber yield and low investment costs, RP1 turned out to be the cheapest propagation method for the cultivation of yacon. The most important cost factors were the procurement of plant material and pre-cultivation. A further mechanization of direct planting of yacon rhizomes (RP2) would offer the chance to decrease the propagation costs within this method significantly.