Abstract
To evaluate if the combined foliar application of nitrogen (N) and zinc (Zn) in broccoli improves the efficiency of the single Zn biofortification, five treatments were tested: (i) control; (ii) one Zn application at the beginning of flowering (0.5M1); (iii) combined 0.5M1 with N application (0.5M1N); (iv) two Zn applications, one at the beginning of the flowering and other after two weeks (0.25 + 0.25) and (v) combined 0.25 + 0.25 with N (0.25N + 0.25N). The Parthenon cultivar showed a good concentration of Ca, Fe, Mg, and Zn, with good bioavailability and glucosinolates, mainly in the florets, and high antioxidant activity and total phenols, mainly in the leaves, showing their potential not only as regards to human consumption, but also for the use of their by-products. All the studied treatments increased floret growth (19%), antioxidant capacity and total phenol content, not affecting Ca, Fe, and Mg concentrations. Glucosinolate content was mostly independent from the studied treatments, decreasing slightly in terms of glucoiberin and the Zn concentration in the florets increased in >50 mg Zn kg−1 in the split treatments and ~40 mg Zn kg−1 when the application was unique, with excellent bioavailability, measured as PA:Zn ratio. Therefore, 0.25 + 0.25 and 0.25N + 0.25N applications have been confirmed as the applications that improve more both growth and accumulation of Zn and biocompounds in broccoli.
Highlights
In the last few years, species of the Brassica genus have become a key part of the human diet, owing to their richness in nutrients and bioactive compounds, and are among the ten most economically important vegetables [1]
Four subsamples of the sieved soil were analyzed, showing pH 6.5 ± 0.1 (10 g soil:25 mL deionized H2 O), and the extractable Zn in the soil was 0.35 ± 0.03 mg kg−1, which was extracted with DTPA [22] and determined by inductively coupled plasma mass spectrometry (ICP-MS)
The application of 0.5% (w/v) ZnSO4 ·7H2 O alone caused a significant increase of 19.2% in the florets compared to the control (11% increase in plant weight)
Summary
In the last few years, species of the Brassica genus have become a key part of the human diet, owing to their richness in nutrients and bioactive compounds, and are among the ten most economically important vegetables [1]. Italica L.) has been shown to be an excellent dietary source of phytochemicals, such as glucosinolates, polyphenols, antioxidants, and essential dietary nutrients (Ca, Mg, Na, K, Fe, and Zn) [1,2,3] Their intake is related to lower risks of developing certain types of cancer, degenerative and cardiovascular diseases, and immune dysfunction [4,5,6]. This richness, though, depends on numerous factors, such as variety, maturation, growing conditions, plant fraction, soil type, storage conditions after harvest, industrial processing, cooking, and the availability of plant nutrients [4]. Zn is used for DNA replication, protein synthesis, catalytic activity, energy transfer reactions, and chlorophyll formation [7,8]
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