Abstract
Many humans lack sufficient zinc (Zn) in their diet for their wellbeing and increasing Zn concentrations in edible produce (biofortification) can mitigate this. Recent efforts have focused on biofortifying staple crops. However, greater Zn concentrations can be achieved in leafy vegetables than in fruits, seeds, or tubers. Brassicas, such as cabbage and broccoli, are widely consumed and might provide an additional means to increase dietary Zn intake. Zinc concentrations in brassicas are limited primarily by Zn phytotoxicity. To assess the limits of Zn biofortification of brassicas, the Zn concentration in a peat:sand (v/v 75:25) medium was manipulated to examine the relationship between shoot Zn concentration and shoot dry weight (DW) and thereby determine the critical shoot Zn concentrations, defined as the shoot Zn concentration at which yield is reduced below 90%. The critical shoot Zn concentration was regarded as the commercial limit to Zn biofortification. Experiments were undertaken over six successive years. A linear relationship between Zn fertiliser application and shoot Zn concentration was observed at low application rates. Critical shoot Zn concentrations ranged from 0.074 to 1.201 mg Zn g−1 DW among cabbage genotypes studied in 2014, and between 0.117 and 1.666 mg Zn g−1 DW among broccoli genotypes studied in 2015–2017. It is concluded that if 5% of the dietary Zn intake of a population is currently delivered through brassicas, then the biofortification of brassicas from 0.057 to > 0.100 mg Zn g−1 DW through the application of Zn fertilisers could increase dietary Zn intake substantially.
Highlights
The relationships between substrate fertiliser Zn concentration, which is less than the actual substrate Zn concentration but is termed ‘substrate Zn concentration’ for brevity, and shoot fresh weight (FW), shoot dry weight (DW) and shoot Zn concentration of cabbage seedlings were studied in experiments performed in 2012, 2013 and 2014 (Table S1)
The experiment performed in 2012 indicated that neither shoot FW nor shoot DW of cabbage genotypes was greatly reduced at substrate concentrations up to 150 mg L−1 and that shoot Zn concentration increased as the substrate Zn concentration was increased (Table S1)
Zn concentrations in cabbage and broccoli reported here generally exceed these values (Table 1). This supports the general hypothesis that greater Zn concentrations can be achieved in leafy vegetables than in seeds, roots or tubers [13]
Summary
It is estimated that over one-fifth of the world’s population suffers from zinc (Zn) deficiency, which results in impaired development, ill health, and a reduction in gross domestic product [1,2,3,4,5].One strategy to increase human dietary Zn intake is to increase Zn concentrations in edible produce.This strategy is termed biofortification and can be achieved through the use of Zn fertilisers on plant genotypes that have greater ability to acquire and accumulate Zn in their edible tissues [1,4,5,6,7,8,9].Zinc might be applied to the soil as inorganic or organic fertilisers or to foliage as soluble salts [1,7,9,10,11].Inorganic fertilisers are often preferred because of their consistent composition; foliar applications are most effective where the phytoavailability of Zn decreases rapidly when applied to the soil [1,5].Recent biofortification efforts have focused largely on developing germplasm and agronomic strategies to increase Zn concentrations in staple crops including cereals, pulses, cassava and potatoes, and Zn. One strategy to increase human dietary Zn intake is to increase Zn concentrations in edible produce. This strategy is termed biofortification and can be achieved through the use of Zn fertilisers on plant genotypes that have greater ability to acquire and accumulate Zn in their edible tissues [1,4,5,6,7,8,9]. Zinc might be applied to the soil as inorganic or organic fertilisers or to foliage as soluble salts [1,7,9,10,11].
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