Localized foliar application of iodine on tomato: An effective approach for targeted agronomic biofortification

Iodine is an essential mineral for the human body and inadequate intake causes iodine deficiency disorders (IDDs) worldwide. Agronomic biofortification is a promising complementary approach to other strategies to avoid IDDs. It consists of the enrichment of fruit and vegetables with nutritional elements through preharvest techniques. Tomato is an important, nutritious, and widely consumed crop. Despite a poor iodine accumulation in the fruit, tomato is an iodine accumulator. Our research focused on iodine enrichment of two table tomato types (cherry and mini-plum) in a commercial mediterranean greenhouse. Potassium iodate (KIO3) was applied four times through foliar spray at three concentrations (0, 1, 5 mM) at two localized sites of application (at plant apex and at the three leaves above the target truss, “target leaves”) until the mature green stage of a target truss (untreated and the same for each treatment). The application of 1 mM KIO3 solution at the target leaves was the most suitable approach for adequate fruit enrichment. The accumulation of 110 μg•100 g−1 of fresh weight (FW) in cherry and 130 μg•100 g−1 FW for mini-plum tomato largely satisfy the iodine recommended dietary allowance for adults, pregnant and lactating women. Plant health, yield and commercial quality of fruit (color, size, dry matter content, total soluble solids, titratable acidity, pH) were not affected, while some carotenoids and total phenolics were slightly incremented, indicating a possible positive influence on the nutritional quality. In conclusion, foliar application of iodine for the preharvest enrichment of tomato was a successful approach to biofortification in a commercial greenhouse. That suggests further research is needed to investigate and improve the iodine biofortification techniques in different crops and systems.