## 1 Introduction  
Perennial wall rocket (_Diplotaxis tenuifolia_ L.--DC.) belongs to Brassicaceae family and is very widespread in the Campania region (southern Italy), accounting for about the 65% of the total national production. This species has remarkable nutritional and anticancer properties, the latter due to the high concentration of glucosinolates (glu-coerucin, 4-methoxyglucobrassicin) that generate bioactive isothi cyanates [1]. The mineral profile is particularly rich, containing potassium (3500 mg 100 g\({}^{-1}\) d.w.), calcium (1200-1800 mg 100 g\({}^{-1}\) d.w.), and iron (15-25 mg 100 g\({}^{-1}\) d.w.) at significantly higher levels than conventional leafy vegetables [2]. Vitamin C content ranges from 50 to 80 mg 100 g\({}^{-1}\) f.w., complemented by substantial folate levels and carotenoids including \(\beta\)-carotene and lutein [3]. Total phenolic compounds (150-300 mg GAE 100 g\({}^{-1}\) f.w. ), predominantly quercetin and kaempfer derivatives, contribute to great antioxidant activity as also observed in other species [4; 5]. The synergy among prebiotic fiber, low caloric density (25 kcal 100 g\({}^{-1}\) f.w. ), and bioactive compounds makes _D. tenuifolia_ a functional food with important potential for cardiovascular protection, gut microbiota modulation, and metabolic health optimization [6]. Nitrate (NO\({}_{3}\)\({}^{-}\)) is the prevailing form of nitrogen available to plants, boosting their growth and development, and an essential component, particularly in the biosynthesis of proteins, nucleic acids, and other nitrogen-containing compounds [6; 7]. Plants accumulate NO\({}_{3}\) in cellular vacuoles, where they participate in metabolic processes and contribute to osmotic regulation, especially under conditions of limited availability of other osmoregulatory compounds [6]. The physiological dynamics of nitrate accumulation in plant tissues are governed by multiple factors, including species characteristics, cell differentiation, fertilization regimes, and light intensity [3; 8]. Leafy vegetables demonstrate pronounced tendency toward NO\({}_{3}\)\({}^{-}\) accumulation and, particularly, rocket (_Diplotaxis tenuifolia_ L.--DC.) is a hyperaccumulator species, with concentrations even exceeding 9000 mg\(\cdot\)kg\({}^{-1}\) fresh [9]. Based on the mentioned implications of nitrate accumulation in leafy vegetables, the European Commission, through the Regulation No. 1258/2011, established the maximum permissible levels of NO\({}_{3}\) in rocket at 6000 mg\(\cdot\)kg\({}^{-1}\) fresh weight in spring-summer and 7000 mg\(\cdot\)kg\({}^{-1}\) fresh weight in autumn-winter [10]. Significant genotypic changes in nitrate accumulation have been observed both within and between cultivated and wild rocket [7; 11], with the latter type frequently displaying higher NO\({}_{3}\) concentrations [11; 12]. However, considering the novelty of wild rocket compared to the historically cultivated _Eruca sativa_ L., its predominant diffusion in Mediterranean areas, and the recent (since 2011) nitrate restrictions imposed by the European Union, the application of biostimulants for nitrate reduction represents a recent interesting research topic for this species. The mentioned differences mainly stem from variations in nitrate uptake mechanisms rather than in reduction capacity, considering that no significant correlation between nitrate accumulation and NO\({}_{3}\) reductase activity has been reported between high- and low-nitrate-accumulating genotypes [13; 14]. Indeed, these uptake variations likely involve differences in nitrate transporter expression/activity (e.g., NRT1/ NRT2 systems) and/or root morphological traits affecting absorption surface area [15].