Differential Response to NaCl Osmotic Stress in Sequentially Harvested Hydroponic Red and Green Basil and the Role of Calcium

Abstract

Basil (Ocimum basilicum L.) is a heterogeneous reservoir of bioactive compounds that provide recognized benefits to human health, rendering it a model aromatic herb. Notwithstanding the application of nutritional stress, such as sodium chloride (NaCl) salinity, which mainly affects the primary metabolism, it also triggers adaptive mechanisms that involve the production of bioactive secondary metabolites. Genotype selection and the exogenous application of calcium chloride (CaCl2) help minimize salinity’s suppressive effects on growth. In the present study, we hypothesize that the ratio of different salt types may induce differential responses in the function of preharvest factors in hydroponic basil culture. In this perspective, the stock nutrient solution (Control) was supplemented with 12.5 mm NaCl + 8.33 mm CaCl2 (Moderate Mix), 25 mm NaCl (Moderate NaCl), 25 mm NaCl + 16.66 of CaCl2 (High Mix), or 50 mM of NaCl (High NaCl) with the objective of evaluating the different impact of salinity on yield, sensory quality (color and aroma profile), and the accumulation of minerals and bioactive compounds in two successive harvests of green and red basil cultivars. Although more productive (+39.0% fresh weight) than the red one, the green cultivar exhibited higher susceptibility to salinity, especially under the High Mix and High NaCl treatments. The addition of CaCl2 to the High Mix solution reduced the sodium by 70.4% and increased the total polyphenols by 21.5% compared to the equivalent isomolar solution (High NaCl). The crop performance in terms of fresh and dry yield improved for both cultivars at the second cut. Regardless of cultivar and salt treatment, successive harvests also increased the concentration of phenols and vitamin C (29.7 and 61.5%, respectively) while reducing (−6.9%) eucalyptol, the most abundant aromatic compound in both cultivars. Salinity, as well as the mechanical stress induced by cutting, improved the functional quality of basil. However, the productive responses to the conditions imposed in our work once again highlighted the importance of genetic background. Specifically, CaCl2 in the Moderate Mix solution preserved fresh leaf weight in the most stress-sensitive green cultivar.

Morpho-Physiological and Biochemical Responses of Hydroponically Grown Basil Cultivars to Salt Stress

“…However, it should be noted that ‘Anise’ and ‘Cinnamon’ did not differ significantly in height, number of leaves, and leaf area, although the total fresh weight was different ( Figure 3 A–C). Relative to total fresh weight, the significant differences observed between cultivars did not result in a different response to salt stress, unlike what Ciriello et al [ 27 ] observed in a recent work on basil. On average, salt treatment reduced the total fresh yield by 51.54% compared to the control; similar results were reported on Salvia officinalis L. [ 28 ] and Mentha spicata L. [ 29 ].…”

Effects of NaCl and CaCl2 as Eustress Factors on Growth, Yield, and Mineral Composition of Hydroponically Grown Valerianella locusta

“…On the other hand, the monovalent inorganic salt, NaCl, did not impair any of the agronomical parameters under low EC conditions. The importance of the osmotic potential on fresh and dry weight has been demonstrated by several studies, most of which focus on the osmotic stress induced by the presence of NaCl, probably due to its association with low irrigation water quality [ 52 , 79 , 80 , 81 , 82 , 83 , 84 , 85 ], and few explore the effects of different salt sources such as KCl, Na 2 SO 4 , or CaCl 2 [ 86 , 87 , 88 , 89 ]. From these studies, the results of Ntatsi et al [ 86 ], who experimented on a salinity tolerant plant, Cichorium spinosum , also showed that under high salinity levels, CaCl 2 had a stronger effect on dry weight, even though under low salinity all the salts decreased both fresh and dry weight equally.…”

“…These thresholds refer to spinach, different types of lettuce, and rucola, and are set from approximately 2000 to a maximum of 5000 mg of NO 3 per kg of fresh weight, depending on the vegetable and season of reference. In the scope of protecting human health and keeping up with EU regulations, it has been suggested from several studies that the demonstrated antagonistic relations of nitrate and chloride can lead to a decreased nitrate content in leafy vegetables and, in several cases, this could be utilized for the production of “safer” foods [ 73 , 77 , 81 , 88 ]. Corn salad is considered a species with a high nitrate content (>2500 mg kg −1 of fresh weight) but its thresholds are not yet defined in the EU regulations [ 13 , 27 , 28 ].…”

Morpho-Anatomical, Physiological, and Mineral Composition Responses Induced by a Vegetal-Based Biostimulant at Three Rates of Foliar Application in Greenhouse Lettuce

“…The quantification of the total phenol concentration of the leaves was determined according to the Folin–Ciocalteu method described by Ciriello et al [ 66 ]. 250 mg of freeze-dried and finely ground leaves were mixed with 10 mL of 60% methanol, shaken (15 min at 4000 rpm), and centrifuged.…”