Evaluation of new clones of Jerusalem artichoke (Helianthus tuberosus L.) for inulin and sugar yield from stalks and tubers

Six clones of Jerusalem artichoke, five new clones (coded as 17, 22, 56, 69 and 70) and the control cultivar "Violette de Rennes" were evaluated for variability in sugars yield, when the plant is utilised as stalk, tuber and "integral crop". Among the above harvesting methods, the integral crop (stalks and tubers at flowering time), showed the highest yield potential of total sugars (fructose+glucose) and inulin (18.6 and 17.9 t/ha, respectively). This was obtained by the clone Violette de Rennes, which also had the greatest inulin chain length, in the text reported as average degree of polymerisation (DP). Clone 69 produced the highest yield of sugars and inulin, when the stalks are harvested at flowering (10.4 and 8.0 t/ha, respectively), while clone 17, with the conventional harvest of tubers at the end of crop cycle, reached 13.3 and 13.7 t/ha of total sugars and inulin, respectively. The average inulin chain length (DP) was highest at flowering time in both stalks and tubers with a range of 7.5-11.2 in the genotypes studied, while, at the final harvest of tubers, it significantly decreased reaching values ranging from 4.8 to 6.7. Among the organs analysed, the tubers at stalk harvest, showed both the highest inulin content and the longest inulin chain, expressed as DP. The genetic variability was very high among the clones for the other characters studied, such as flowering time, sugar content in different organs, photosynthesis activity, leaf chlorophyll content, etc. In particular, the "refractometrically measured" solids, in extracted tissue juice, expressed as the Brix-value (a very quick method), exhibited a significant positive relationship with the tuber inulin content (0.90** and 0.85**, n=6, in the first and second harvest, respectively), confirming its suitability as a fast screening method in breeding, avoiding time consuming and expensive laboratory analysis.