Response of growth, productivity, and active constituents of Hyssopus officinalis to irrigation and salicylic acid foliar application

Background As hyssop was recently introduced for cultivation in Egypt, it is recommended to know its optimal agronomic management practices, especially the irrigation management. Objective This work demonstrates the effect of the number of irrigation times per week and foliar spraying of different concentrations of salicylic acid and the interaction between them on the hyssop planted in sandy soil and under the drip irrigation system. Materials and methods In the 2-year experiment, three irrigation treatments, that is, once, twice, and three times per week, were applied with three concentrations of salicylic acid (0, 100, and 200 ppm). The growth parameters, photosynthetic pigments, antioxidant activity, total phenolics, proline content, essential oil percentage, and yield along with the main constituents of the essential oil were studied in hyssop herb to find out the relationship between these characteristics and the applied treatments. Results and conclusion It was observed that increasing the number of irrigation times from once to twice and three times per week increased growth, yield, essential oil percentage (%), content (ml/plant), and yield (l/ha) significantly in both seasons, except essential oil (%) from plants irrigated twice per week in the first season, which increased insignificantly. The essential oil showed the main compounds as 3-pinanone, cis in most treatments, except plants irrigated twice and three times per week and sprayed with tap water, where the main component was trans-3-pinanone (38.70 and 32.94 %, respectively). 3-pinanone, cis relative percent ranged from 40.81 to 63.47% in plants irrigated once per week and from 16.78 to 58.49 % in plants irrigated at twice per week, and then from 30.17 to 47.56 % in plants irrigated three times per week. Oxygenated compounds increased under water deficit (once per week) and decreased with increasing salicylic acid concentration. It may be concluded that hyssop plants that were irrigated twice per week and sprayed with 100 ppm salicylic acid produced the highest yield of both herb and essential oil.