Enhancing the Growth of Artemisia abrotanum by Magnesium and Tropaeolum majus Extract in a Field Experiment Along with the Antibacterial Activity of the Isolated Essential Oils

Enhancing the growth and productivity of ornamental and horticultural plants is a major function of plant extracts and macronutrient elements. The growth properties of Artemisia abrotanum plants were evaluated in two successive seasons as affected by the magnesium (Mg) fertilizer added to the soil in the form of magnesium sulfate at four concentrations of 0 (as a control), 4, 6, and 8 g/L as well as Tropaeolum majus aqueous leaf extract (ALE) at concentrations of 0 (as a control), 4, 6, and 8 g/L as a foliar application. The chemical components of A. abrotanum essential oils (EOs) were analyzed using the gas chromatography–mass spectrometry (GC-MS) apparatus. The studied parameters, including plant height, total fresh weight, number of branches/plant, EO percentages, chlorophyll-a content, chlorophyll-b content, and carotenoid content, were enhanced by the application of Mg or T. majus ALE or their combinations. The highest plant heights, 48.83 cm, and 48.5 cm, were observed in the plants treated with Mg (8 g/L)+T. majus ALE (8 g/L) and Mg (6 g/L)+T. majus ALE (4 g/L), in both seasons, respectively. The highest values of total fresh weight, 54.80 and 60.59 g, were recorded in plants treated with Mg (8 g/L)+T. majus ALE (4 g/L) and Mg (8 g/L)+T. majus ALE (4 g/L), in both seasons, respectively. The highest number of branches/plant, 60.33 and 73.33, were measured in plants treated with Mg (8 g/L)+T. majus LAE (8 g/L), in both seasons, respectively. The highest EO percentages, 0.477% and 0.64%, were measured in plants treated with Mg (8 g/L)+T. majus ALE (8 g/L), in both seasons, respectively. The total fresh weight in both seasons (r = 0.96), the number of branches/plant in both seasons (r = 0.97), the number of branches/plant in the first season, and the number of branches/plant in both seasons (r = 0.96), the total fresh weight in the second season and the number of branches/plant in the first season (r = 0.95) and the second season (r = 0.94), and the number of branches/plant and the carotenoids in the first season (r = 0.90) were all found to be significantly and positively correlated. The major compounds in the EOs were 7-methoxy-4-methylcoumarin (4-methylherniarin), cedrol, endo-borneol, and 7-epi-silphiperfol-5-ene. The antibacterial activity of the EOs was evaluated against the growth of Pectobacterium atrosepticum and Pectobacterium carotovorum subsp. carotovorum, which causes soft rot of potato tubers. The EOs were found to be effective against P. carotovorum subsp. carotovorum with the inhibition zones ranging from 1 to 5 mm at the concentration of 100 μg/mL, and no inhibitions were found against P. atrosepticum at the studied concentrations. The minimum inhibitory concentration against P. carotovorum subsp. carotovorum was found at 75 μg/mL. In conclusion, using the combination treatments of Mg and T. majus ALE is highly suggested to enhance the growth of A. abrotanum plants.