Harvest Dates, Fertilizer and Varietal Effects on Yield, Concentration and Molecular Distribution of Fructan in Jerusalem Artichoke (Helianthus tuberosus L.)

In a pot experiment two varieties of Jerusalem artichoke ( Helianths tuberosus L., cv. Topianka and cv. Violet de Rennes ) were exposed to different supplies of N, P and K. Nitrogen supply increased tuber yield more than the productivity of aerial parts. Violet de Rennes responded better to N than Topianka. Nutrient regimes without P or K addition but including N to some extent depressed the yields of tubers only (by 8–23 %). Carbohydrate concentrations (78–81 % of d.m.) and molecular fructan distributions were neither influenced by fertilizer regimes nor by mineral concentrations in the tubers.
Genotypic differences were significant for yield, for concentrations of N, P, Ca, S and Cu, and for fructan concentration in the tubers. At harvest time the fructose/glucose ratio in tubers of Violet de Rennes was about 10 % higher than in Topianka and remained on a higher level during storage.
Harvest time had the greatest influence on carbohydrate composition. Depolymerization of fructan proceeded at a high rate in November and slowed down during subsequent storage, accompanied by a decline in polydispersity. Simultaneously osmolanty increased, resulting in a freezing point depression of < 0.5 °C.