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.
Highlights
Basil (Ocimum basilicum L.) is a native herbaceous plant of southern Asia, known as the “king of herbs” for its fragrant, delightful, and colorful leaves (Ciriello et al, 2020; Formisano et al, 2021b)
Superior leaf number but smaller leaf area and leaf fresh weight (FW) were observed in Red, reflecting the smaller leaves of this cultivar compared to Green, whereas leaf dry matter (DM) percentage and dry weight (DW) were not influenced by cultivar type
Salinity treatments had no effect on the leaf number and leaf DM percentage; the High Mix treatment and the High NaCl treatment suppressed the leaf area, leaf FW, and DW, which signals a deleterious effect on plant growth under both high-salt treatments
Summary
Basil (Ocimum basilicum L.) is a native herbaceous plant of southern Asia, known as the “king of herbs” for its fragrant, delightful, and colorful leaves (Ciriello et al, 2020; Formisano et al, 2021b). It is used to treat indigestion and as a vermifuge due to its bioactive content and high nutraceutical value (Ch et al, 2015) These secondary metabolites of aromatic herbs are a precious reservoir of bioactive molecules that the pharmaceutical industry could use to develop new drugs and improve their natural chemical diversity (David et al, 2015). In this respect, recent scientific research has highlighted how genotype and agronomic practices, such as successive harvests, can be a valuable tool toward increasing the levels of desired secondary metabolites (Nicoletto et al, 2013; Ciriello et al, 2021a,b)
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