Iodine Biofortification of Apples and Pears in an Orchard Using Foliar Sprays of Different Composition

Abstract

Many people across the world suffer from iodine (I) deficiency and related diseases. The I content in plant-based foods is particularly low, but can be enhanced by agronomic biofortification. Therefore, in this study two field experiments were conducted under orchard conditions to assess the potential of I biofortification of apples and pears by foliar fertilization. Fruit trees were sprayed at various times during the growing season with solutions containing I in different concentrations and forms. In addition, tests were carried out to establish whether the effect of I sprays can be improved by co-application of potassium nitrate (KNO3) and sodium selenate (Na2SeO4). Iodine accumulation in apple and pear fruits was dose-dependent, with a stronger response to potassium iodide (KI) than potassium iodate (KIO3). In freshly harvested apple and pear fruits, 51% and 75% of the biofortified iodine was localized in the fruit peel, respectively. The remaining I was translocated into the fruit flesh, with a maximum of 3% reaching the core. Washing apples and pears with running deionized water reduced their I content by 14%. To achieve the targeted accumulation level of 50–100 μg I per 100 g fresh mass in washed and unpeeled fruits, foliar fertilization of 1.5 kg I per hectare and meter canopy height was required when KIO3 was applied. The addition of KNO3 and Na2SeO4 to I-containing spray solutions did not affect the I content in fruits. However, the application of KNO3 increased the total soluble solids content of the fruits by up to 1.0 °Brix compared to the control, and Na2SeO4 in the spray solution increased the fruit selenium (Se) content. Iodine sprays caused leaf necrosis, but without affecting the development and marketing quality of the fruits. Even after three months of cold storage, no adverse effects of I fertilization on general fruit characteristics were observed, however, I content of apples decreased by 20%.

Preharvest iodine sprays at high rates are more effective in biofortification of apples than soil application

“…Leaf damage was manifested as necrosis along leaf edges and as small, irregular necrotic spots throughout the lamina, identical to those observed by Budke et al (2020aBudke et al ( , 2021 for apple leaves sprayed with I solutions. The intensities of I-sprayed leaf injuries for a given rate were comparable for both I species.…”

“…m CH) −1 ] caused leaf damage to 25% of the leaf area (Table 3). Considerable differences in the susceptibility of apple leaves to burns as a result of the sprays recorded by Budke et al (2020aBudke et al ( , 2021 and in the present experiment could result from different tree growth conditions (such as air temperature, humidity, rainfall and light intensity), tree growth stage and the I rates used as has been reported by Świetlik and Faust (1984). It is worth noting that in our experiment, damage of leaves was not affected by the I form even though the spray solution I concentrations containing KIO 3 were 31% higher compared with those with the use of KI.…”

“…Simultaneously, applications of KI or K-iodate (KIO 3 ) to peat-based substrate in which trees grew were not able to effectively increase apple I concentrations. In a subsequent study by Budke et al (2021), carried out in 'Jonagold' and 'Fuji' apple orchards, the authors found that the I sprays applied two times in the summer or once 2 weeks before harvest at rates of 0.25-2.5 kg I [ha . meter canopy height -(CH) −1 ] were able to increase apple I concentrations to about 200 µg 100 g −1 fresh weight (FW).…”

“…), pear (Pyrus communis L.) and apple (Malus domestica Borth.) trees (Budke et al 2020a(Budke et al , 2021Caffagni et al 2012). In particular, apples appear to be good targets for I biofortification because they are widely consumed throughout the world and have high contents of dietary antioxidants that play an important role in human health (Boyer and Liu 2004).…”

Pre-Launch Exploration of Consumer Willingness to Purchase Selenium- and Iodine-Biofortified Apples—A Discrete Choice Analysis of Possible Market Settings

“…This technique proved to be effective in increasing the selenium and iodine content in plant-based food [ 13 , 14 ]. Recently, field experiments have been successfully carried out for apples and other fruits [ 15 , 16 , 17 , 18 ]. D’Amato et al compiled numerous attempts of biofortification of food crops with selenium.…”