Jerusalem artichoke (Helianthus tuberosus, L.) maintains high inulin, tuber yield, and antioxidant capacity under moderately-saline irrigation waters

Authors: DIAS, NILDO - Federal Rural University Of The Semi-Arid; Ferreira, Jorge; Liu, Xuan; Suarez, Donald

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2016
Publication Date: 9/29/2016
Citation: Dias, N.S., Ferreira, J.F., Liu, X., Suarez, D.L. 2016. Jerusalem artichoke (Helianthus tuberosus, L.) maintains high inulin, tuber yield, and antioxidant capacity under moderately-saline irrigation waters. Industrial Crops and Products. 94:1009-1024. https://doi.org/10.1016/j.indcrop.2016.09.029.
DOI: https://doi.org/10.1016/j.indcrop.2016.09.029

Interpretive Summary: The scarcity of good quality water in semiarid regions of the world is the main limiting factor for increased irrigated agriculture in those regions, but saline water is generally widely available. The literature provides few management strategies and alternative food crops that can be grown with saline waters. Jerusalem artichoke is widely used as a low-calorie food, and as raw material for the prebiotic inulin and biofuels in several countries, but not in the United States. The crop is cited as moderately tolerant to salinity and drought, but the effect of salinity on inulin and the antioxidant capacity of tubers has not been studied. Plants were irrigated with waters with electrical conductivity (EC) ranging from 1.2 dS/m (control) to 12 dS/m blending fresh and saline water. Both growth and tuber yield were reduced in response to increased salinity. Results indicate that salinity affects shoot development more severely than tuber yield for cultivar Stampede and that it can tolerate salinity up to 6.6 dS/m with only a small decrease in tuber yield. Tuber (but not shoot) yield of Stampede can be maintained if irrigation waters of EC=12 dS/m are applied in the final 25% of the growing cycle, thus saving 25% of fresh water. Increased salinity had no significant effect on tuber starch and fructose, but caused a decrease in sucrose and glucose and an increase in inulin (from 50 to over 60% of tuber dry weight). Salinity slightly increased antioxidant capacity (ORAC and total phenolics) of tubers up to 9 dS/m indicating that antioxidants may be a form of defense against oxidative stress caused by salinity. Stampede is an early cultivar that adapted well to moderate salinity (EC=6.6 dS/m) of irrigation water, producing in average 1.4kg of tubers per plant, over 50% of fructans/tuber DW, being a rich source of the prebiotic inulin for the food and biofuel industries. These results are important for production of human food, animal feed, and raw material for both food and biofuel industries in areas where fresh water is insufficient for irrigation, and are of interest to producers, consultants and farmer advisors dealing with biofuels or inulin (used as a prebiotic and natural sweetener).

Technical Abstract: The scarcity of good quality water in semiarid regions of the world is the main limiting factor for increased irrigated agriculture in those regions. Saline water is generally widely available in arid regions at reduced costs, and can be a viable alternative for crop irrigation. However, the literature provides few management strategies and alternative crops that can be grown with saline waters. Our objective was to investigate the effects of saline water blended with low-salinity water (LSW), or high-salinity water (HSW) applied sequentially with LSW for irrigation of Jerusalem artichoke (Helianthus tuberosus L., cv. Stampede). Plants were irrigated with blended waters with electrical conductivity (EC) ranging from 1.2 dS/m (control) to 12 dS/m or with LSW followed by HSW at set intervals, and sequentially applied. The experiment was conducted in large outdoor sand tanks. Both growth and tuber yield were reduced in response to increased salinity, but no significant difference was found among treatments higher than the LSW control, including sequential treatments where HSW was substituted for LSW. An increase in salinity from 1.2 to 6.6 dS/m reduced shoot biomass by 37.5%, but tuber yield was only reduced by 13%. However, increasing salinity to 12 dS/m led to a 67% decrease in shoot and 49% decrease in tuber production. Results indicate that salinity affects shoot development more severely than tuber yield for Stampede and that it can tolerate salinity of 6.6 dS/m (in a well-drained soil) with only a small decrease in tuber yield. Regarding sequential use of LSW followed by HSW, only the treatment where LSW was used for 75% of the irrigations resulted in tuber yield similar to the ones achieved with LSW used during all crop cycle. There was no statistical difference for shoot biomass in using LSW followed by HSW compared to blended waters of equivalent salinity. Our results indicate that tuber yield of Stampede can be maintained if irrigation waters of EC=12 dS/m are applied in the final 25% of the growing cycle, and if the crop receives at least 75% of initial irrigations with LSW. Thus, it would be possible to save 25% of fresh water needed for tuber yield. As salinity increased, Stampede sequestered most sodium in roots and tubers, but chloride increased with salinity in all organs, being higher in roots and leaves. Mineral composition of shoots and roots was maintained at an adequate level for plant growth and for tuber development under elevated salinity suggesting that 1) leaves and roots are the main sinks for nutrients and that 2) the decrease in shoot and tuber biomass could be due to the toxic effects of chloride rather than to mineral deficiency. Salinity had no significant effect on tuber sugars, except for a correspondent sharp decrease in sucrose and an increase in inulin (to >50% of tuber DW). Salinity had no effect on the antioxidant capacity (ORAC and total phenolics) of tubers. Stampede is an early cultivar that adapted well to moderate salinity (EC=6.6 dS/m) of irrigation water, producing in average 1.4kg of tubers, over 50% of fructans/tuber DW, and to be a rich source of the prebiotic inulin, sugars for the food industry, or as raw material for biofuels. Late-developing cultivars can also produce enough shoot and root biomass to be used as a source of biofuels under moderate salinity.