A field experiment undertaking in spring 2022 assessed the impact of seven NPK fertilizer combinations on the gene expression and biochemical compounds of two Roselle (Hibiscus sabdariffa L.) cultivars, held at the Kerbala Governorate, Iraq. The randomized complete block design (RCBD) layout had two factors and three replications. The first factor included NPK fertilizer combinations, while the second factor was the two Roselle cultivars (Iraqi-1 and Iraqi-2). The results showed cultivar Iraqi-2 contains missense mutations in codons 23 and 61 (CCA → CTA and ATT → AGT, respectively), which encode for amino acids (Pro → Leu and Ile → Ser, respectively) in the CHS gene. Missense mutations were also evident in codons 80 and 100 (TTG → TTC and CCA → TCA, respectively), encoding amino acids (Leu → Phe and Pro → Ser, respectively) in the F3H gene of the same cultivar. Cultivar Iraqi-1 proved superior in vitamin C, quercetin, hibiscetin, and gossypetin, with average values of 37.87, 0.387, 0.386, and 0.186 mg g^-1, respectively. In fertilizer combinations, combination 6 excelled in all the above-mentioned traits, with averages of 44.42, 0.410, 0.451, and 0.250 mg g^-1, respectively. The interaction between the factors was significant for all the traits under study.

Keywords: Roselle (H. sabdariffa L.), NPK fertilizer combinations, cultivars, gene expression, biochemical compounds

Key findings: The NPK combination (175:150:150 kg ha^-1) excelled in almost all the characteristics of Roselle (H. sabdariffa L.). The cultivar Iraqi-1 of Roselle was significantly superior for the studied characteristics. Therefore, before application, it is crucial to determine the balance among the macronutrients.