Optimized Nutrition as a Driver of Cultivar-Specific Metabolic Plasticity in Sweet Basil

Sweet basil is a medicinal herb valued for its culinary and therapeutic applications, primarily due to its secondary metabolite content. Therefore, optimizing its cultivation is essential for growers seeking to improve both the quality and nutritional value of the plants. Two cultivars of Ocimum basilicum L., ‘Lettuce Leaf’ (LL) and ‘Purple Opal’ (PO), were evaluated under various nutritional regimes (mineral, organic, and organo-mineral). The assessment included measurements of total protein, fat, and ash content, as well as total polyphenol levels, phenolic acid content, and antioxidant activity. HPLC analysis was performed to evaluate the composition of selected phenolic and chlorogenic acids, flavonoids, and catechins. Additionally, mineral content was analyzed using OES-ICP. Gene expression of key genes involved in the phenylpropanoid pathway (PAL, C4H, 4Cl, CAD, and CVOMT) and the transcription factor OscWRKY1 was analyzed through RT-qPCR. The key findings indicated that the nutritional variants significantly impacted both primary and secondary metabolism in the assessed plants. Additionally, there was a significant (p < 0.05) cultivar-specific response to the different nutritional variants. The results suggest that the optimal nutritional strategy may vary depending on the target metabolite. Variant 4 was associated with the most favorable overall response in basil, including increased protein levels, higher total polyphenol content, and a balanced mineral composition. However, variant 5 showed the highest antioxidant activity for both cultivars. Rutin and protocatechuic acid were detected only in PO, and cryptochlorogenic acid was detected only in LL. A marked varietal difference was observed in gallocatechin content, with the LL variety containing more than fourfold higher levels than the PP variety. The results of RT-qPCR were fluctuating and strongly dependent on the cultivar.