Tuber and Inulin Production of Jerusalem Artichoke (Helianthus tuberosus, L.) Under Salinity Stress.

Salinization of soils and irrigation waters has increased soil salinity worldwide, and threaten to reduce crop yield.   In the semiarid regions, fresh water scarcity demands salt- and drought-tolerant crops. Jerusalem artichoke (cv. Stampede), a North American crop with inulin-rich tubers, is a carbon source for biofuels and for pre-biotic, low-calorie, soluble fiber (nutraceutical value). Although previous workers studied the effect of salinity on tuber yield, only one evaluated salinity effect on inulin yield, and none on its degree of polymerization (DP). Plants were grown in 9m³ outdoor sand tanks for four months being submitted to salinity 30 days after planting. Salinity (as water electrical conductivity, EC_w) increase from EC_w=1.2 to 12 dS/m reduced shoot and tuber biomass by 67% and 49%, respectively, while EC_w=6.6 dS/m reduced shoot biomass by 37.5%, but tuber biomass  only by 13% indicating that ‘Stampede’ tolerates moderate salinity with minor tuber yield loss.  Inulin tuber dry weight concentration (50-60%) and its DP were unaffected by salinity, even at EC_w =12 dS/m. Based on elemental analyses, and despite increasing salinity, Na⁺ accumulated only in roots and tubers, but not in leaves or stems, while Cl^- increased in all organs, mainly roots and leaves.  As nutrient levels remained constant in shoots and roots, we propose that Cl^-, not Na⁺, was the most toxic ion for this crop. The early-flowering ‘Stampede’ completed its production cycle in four months, suggesting its adaptability to areas with short summers and with moderate saline waters or soils. At EC_w=6.6 dS/m ‘Stampede’ produced (with 2.2 plants/m²) 1.4kg tuber/plant (15.5 tons inulin/ha), being a highly attractive source of inulin for biofuels or for the functional food market. Its moderate tolerance to salinity keeps it from competing with lands used to produce conventional agricultural crops.