Iodine Fortification Plant Screening Process and Accumulation in Tomato Fruits and Potato Tubers

Iodine is an essential microelement for human health, and the recommended daily allowance (RDA) of such element should range from 40 to 200 g day-1. Because of the low iodine contents in vegetables, cereals, and many other foods, iodine deficiency disorder (IDD) is one of the most widespread nutrient-deficiency diseases in the world. Therefore, investigations of I uptake in plants with the aim of fortifying them can help reach the important health and social objective of IDD elimination. This study was conducted to determine the effects of the absorption of iodine from two different chemical formspotassium iodide (I-) and potassium iodate (IO-3)in a wide range of wild and cultivated plant species. Pot plants were irrigated with different concentrations of I- or IO-3, namely 0.05% and 0.1% (w/v) I- and 0.05%, 0.1%, 0.2%, and 0.5% (w/v) IO-3. Inhibiting effects on plant growth were observed after adding these amounts of iodine to the irrigation water. Plants were able to tolerate high levels of iodine as IO-3 better than I- in the root environment. Among cultivated species, barley (Hordeum vulgare L.) showed the lowest biomass reductions due to iodine toxicity and maize (Zea mays L.) together with tobacco (Nicotiana tabacum L.) showed the greatest. After the screening, cultivated tomato and potato were shown to be good targets for a fortification-rate study among the species screened. When fed with 0.05% iodine salts, potato (Solanum tuberosum L.) tubers and tomato (Solanum lycopersicum L.) fruits absorbed iodine up to 272 and 527 g/100 g fresh weight (FW) from IO-3 and 1,875 and 3,900 g/100 g FW from I-. These uptake levels were well more than the RDA of 150 g day-1 for adults. Moreover, the agronomic efficiency of iodine accumulation of potato tubers and tomato fruits was calculated. Both plant organs showed greater accumulation efficiency for given units of iodine from iodide than from iodate. This accumulation efficiency decreased in both potato tubers and tomato fruits at iodine concentrations greater than 0.05% for iodide and at respectively 0.2% and 0.1% for iodate. On the basis of the uptake curve, it was finally possible to calculate the doses of supply in the irrigation water of iodine as iodate (0.028% for potato and 0.014% for tomato) as well as of iodide (0.004% for potato and 0.002% for tomato) to reach the 150 g day-1 RDA for adults in 100 g of such vegetables, to efficiently control IDD, although these results still need to be validated.