Foliar application of selenium and humic acid changes yield, essential oil, and chemical composition of Plectranthus amboinicus (Lour.) plant and its antimicrobial effects

Background and objective Plectranthus amboinicus is an indigenous vegetable that can be freshly eaten. This plant is used for medicine to cure common illnesses such as cough, stomachache, headache, and skin infection. Materials and methods This study was conducted to study the effect of both selenium (2, 4, 8, 12, and 16 g/l) and humic acid (1.5 and 3.00 g/l), in addition to control, which was sprayed with water. Results and conclusion Generally, mass production of P. amboinicus (Lour.) plants has significantly increased as a result of application of different levels of selenium and humic acid treatments, compared with the control treatment. Essential oil percentage and yield (ml/plant) increased significantly as a result of selenium and humic acid treatments compared with control (S0H0). For essential oil constituents, the results clear that carvacrol (5.96–15.45%) is the first main compound followed by γ-Terpinene (6.74–11.80 %). The third main component is Limonene (3.23–11.32%), whereas the fourth one is α-Muurolene. Moreover, these treatments had a positive effect on selenium, total carbohydrates, photosynthetic pigments, and total phenolic content. Based on scavenging the stable ATBS [2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)] radical, all treatments increased significantly inhibition % especially S4H2 compared with untreated plants. Antibacterial and antifungal activities of P. amboinicus were studied.