Enhancing the Growth of <i>Artemisia abrotanum</i> by Magnesium and <i>Tropaeolum majus</i> 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 <i>Artemisia abrotanum</i> 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 <i>Tropaeolum majus</i> 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 <i>A. abrotanum</i> 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 <i>T. majus</i> 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)+<i>T. majus</i> ALE (8 g/L) and Mg (6 g/L)+<i>T. majus</i> 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)+<i>T. majus</i> ALE (4 g/L) and Mg (8 g/L)+<i>T. majus</i> 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)+<i>T. majus</i> 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)+<i>T. majus</i> 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 <i>Pectobacterium atrosepticum</i> and <i>Pectobacterium carotovorum</i> subsp. <i>carotovorum</i>, which causes soft rot of potato tubers. The EOs were found to be effective against <i>P. carotovorum</i> subsp. <i>carotovorum</i> with the inhibition zones ranging from 1 to 5 mm at the concentration of 100 μg/mL, and no inhibitions were found against <i>P. atrosepticum</i> at the studied concentrations. The minimum inhibitory concentration against <i>P. carotovorum</i> subsp. <i>carotovorum</i> was found at 75 μg/mL. In conclusion, using the combination treatments of Mg and <i>T. majus</i> ALE is highly suggested to enhance the growth of <i>A. abrotanum</i> plants.