Iodine biofortification of wheat, rice and maize through fertilizer strategy
Iodine (I) deficiency is distinct from other micronutrient deficiencies in human populations in having a high endemic prevalence both in well-developed and in developing countries. The very low concentration of iodine in agricultural soils and cereal-based foods is widely believed to be the main reason of iodine deficiency in humans, especially in developing countries. In the present study, the possibility of using iodine containing fertilizers for agronomic biofortification of cereal grains with iodine was studied. The aim was to establish the best application method (to the soil or as foliar spray), the best form of iodine (potassium iodate or potassium iodide) and the optimal dose of iodine. Additionally, experiments were conducted to study transport of iodine in plants and localization of iodine within the grains.
Materials and methods
Experiments were conducted both under greenhouse conditions and in the field on wheat (Triticum aestivum) grown in Turkey and Pakistan, on rice (Oryza sativa) grown in Brazil, Thailand and Turkey and on maize (Zea mays) grown in Turkey. The iodine concentration in the grain, localization of iodine in different grain fractions of wheat (i.e., endosperm, bran and embryo) and iodine concentration of both brown rice and polished rice was analyzed. In short-term experiments, the translocation of iodine from older into younger leaves was also studied. Inductively coupled plasma mass spectrometry (ICP-MS) was used for analysis of iodine in plant and soil samples.
In greenhouse experiments on wheat, soil-applied potassium iodide (KI) and potassium iodate (KIO3) at increasing rates (i.e., 0, 0.1, 0.25, 1, 2.5, 5, 10 and 20 mg I kg−1 soil) both iodine forms substantially increased iodine concentration in the shoot, with the highest shoot iodine resulting from the KI treatments. However, these soil treatments did not affect iodine concentrations in the wheat grain, with the exception of the highest iodine rates (i. e., 10 and 20 mg I kg−1 soil) which also depressed the grain yield. In contrast to the soil applications, foliar spray of KI and KIO3 at increasing rates during heading and early milk stages did enhance grain iodine concentrations up to 5- to 10-fold without affecting grain yield. Including KNO3 or a surfactant to the iodine containing foliar spray further increased the grain iodine concentration. In a short-term experiment using young wheat plants, it was found that iodine is translocated from older into younger leaves after immersion of the older leaves in solutions containing KI or KIO3. Adding KNO3 or a surfactant in the immersion solution also promoted leaf absorption and translocation of iodine into younger leaves. Field experiments conducted in different countries confirmed that foliar application with increasing rates of iodine significantly increased grain iodine concentrations in wheat, brown rice and maize. This increase was also found in the iodine concentration of the endosperm part of wheat grains and in polished rice.
The results of the present study clearly show that foliar application of iodine containing fertilizers is highly effective in increasing grain iodine concentrations in wheat, rice and maize. Presented results suggest that iodine is translocated from shoot to grain by transport in the phloem. Spraying KIO3 up to the rate of 0.05% w/v is suggested as the optimal form and rate to be used in agronomic biofortification with iodine. The substantial increase in grain iodine concentrations could contribute to the prevention of iodine deficiency in human populations with low dietary iodine intake. The reasons behind the higher effectiveness of foliar-applications compared to the soil applications of iodine fertilizers in improving grain iodine concentration are discussed.
KeywordsAgronomic biofortification Iodine Maize Potassium iodate Potassium iodide Potassium nitrate Rice Surfactant Wheat
This study has been financially supported by SQM, Nestlé and International Fertilizer association (IFA) and benefited also from the activities of the on-going HarvestZinc Project (www.harvestzinc.org) that is supported by the HarvestPlus Program, SQM, ADOB, Bayer Cropscience, Mosaic Company, K + S Kali, International Fertilizer Industry (IFA), Valagro, ICL Fertilizers, ATP Nutrition, International Zinc Association (IZA), Aglukon and International Plant Nutrition Institute (IPNI).
- Gimeno V, Diaz-Lopez L, Simon-Grao S, Martinez V, Martinez-Nicolas JJ, Garcia-Sanchez F (2014) Foliar potassium nitrate application improves the tolerance of Citrus Macrophylla L. seedlings to drought conditions. Plant Physiol Biochem 83:308–315. doi: 10.1016/j.plaphy.2014.08.008 CrossRefPubMedGoogle Scholar
- Hossain MZ, Amin MR, Bhuiyan MS, Rahaman MA (2008) Performance of glutinous rice varieties of coastal region in Bangladesh. South Asian J Agric 3:111–114Google Scholar
- Hu Q, Moran JE, Blackwood V (2009) Geochemical cycling of iodine species in soils. In: Preedy VR, Burrow GN, Watson R (eds) Comprehensive handbook of iodine nutritional, biochemical, pathological and therapeutic aspects. Academic Press, Oxford, pp 93–105Google Scholar
- Hurtevent P, Thiry Y, Levchuk S, Yoschenko V, Henner P, Madoz-Escande C, Leclerc E, Colle C, Kashparov V (2013) Translocation of 125I, 75Se and 36Cl to wheat edible parts following wet foliar contamination under field conditions. J Environ Radioact 121:43–54. doi: 10.1016/j.jenvrad.2012.04.013 CrossRefPubMedGoogle Scholar
- Johnson CC (2003) The Geochemistry of Iodine and its Application to Environmental Strategies for Reducing the Risk from Iodine Deficiency Disorders. British Geological Survey DFID Kar project R7411, Report CR/03/057NGoogle Scholar
- Lyons G, Cakmak I. (2012) Agronomic biofortification of food crops with micronutrients, In Bruulsema TW et al (eds). Fertilizing crops to improve human health: a scientific review. First edition, International Plant Nutrition Institute & International Fertilizer Industry Association. IPNI, Norcross, Georgia, USA/IFA, Paris, France, pp 97–122Google Scholar
- Marschner P (2012) Marschner’s mineral nutrition of higher plants, 3rd edn. Elsevier, Academic PressGoogle Scholar
- Medrano-Macias J, Leija-Martinez P, Gonzalez-Morales S, Juarez-Maldonado A, Benavides-Mendoza A (2016) Use of iodine to biofortify and promote growth and stress tolerance in crops. Front Plant Sci 7. doi: 10.3389/fpls.2016.01146
- Mello, PA, Barin JS, Duarte,FA. Bizzi CA, Diehl LO, Muller EI, Flores EM (2013) Analytical methods for the determination of halogens in bioanalytical sciences: a review. Anal Bioanal Chem 405:7615–7642.Google Scholar
- Pearce EN, Lazarus JH, Moreno-Reyes R, Zimmermann MB (2016) Consequences of iodine deficiency and excess in pregnant women: an overview of current knowns and unknowns. Amer J clinic Nutr 104 (supplement 3): 918S-923S. doi: 10.3945/ajcn.115.110429
- Shen C, Ding Y, Lei X, Zhao P, Wang S, Xu Y, Dong C (2016) Effects of foliar potassium fertilization on fruit growth rate, potassium accumulation, yield, and quality of ‘Kousui’ japanese pear. HortTechnol 26:270–277Google Scholar
- Smolen S, Skoczylas L, Ledwozyw-Smolen I, Rakoczy R, Kopec A, Piatkowska E, Biezanowska-Kopec R, Koronowicz A, Kapusta-Duch J (2016) Biofortification of carrot (Daucus carota L.) with iodine and selenium in a field experiment. Front Plant Sci 7. doi: 10.3389/fpls.2016.00730
- Southwick SM, Olson W, Yeager J, Weis KG (1996) Optimum timing of potassium nitrate spray applications to French prune trees. J Am Soc Hortic Sci 121:326–333Google Scholar
- Welch RM, Graham RD, Cakmak I (2013) Linking agricultural production practices to improving human nutrition and health. FAO/WHO, RomeGoogle Scholar
- Zheng Y, Xu X, Simmons M, Zhang C, Gao F, Li Z (2010) Responses of physiological parameters, grain yield, and grain quality to foliar application of potassium nitrate in two contrasting winter wheat cultivars under salinity stress. J Plant Nutr Soil Sci 173(3):444–452. doi: 10.1002/jpln.200900313 CrossRefGoogle Scholar
- Zou CQ, Zhang YQ, Rashid A, Ram H, Savasli E, Arisoy RZ, Ortiz-Monasterio I, Simunji S, Wang ZH, Sohu V, Hassan M, Kaya Y, Onder O, Lungu O, Yaqub Mujahid M, Joshi AK, Zelenskiy Y, Zhang FS, Cakmak I (2012) Biofortification of wheat with zinc through zinc fertilization in seven countries. Plant Soil 361:119–130. doi: 10.1007/s11104-012-1369-2 CrossRefGoogle Scholar