How to Cite: Fouad, H., Elsayed, S. I. M., Fouad, R., Hendawy, S. F., & Omer, E. A. (2022). Influence of exogenous tryptophan application on production and carotenoids of Calendula officinalis under drip irrigation treatments. International Journal of Health Sciences, 6(S6), 10840– 10852. https://doi.org/10.53730/ijhs.v6nS6.12936 International Journal of Health Sciences ISSN 2550-6978 E-ISSN 2550-696X © 2022. Manuscript submitted: 9 May 2022, Manuscript revised: 18 July 2022, Accepted for publication: 27 August 2022 10840 Influence of exogenous tryptophan application on production and carotenoids of Calendula officinalis under drip irrigation treatments Hend Fouad Medicinal and Aromatic Plants Research Department, National Research Centre, 33 Elbouhouth St., Dokki, Giza, Egypt *Corresponding author email: hendfouad12@yahoo.com Shaimaa I. M. Elsayed Horticultural Crops Technology Department, National Research Centre, 33 Elbouhouth St., Dokki, Giza, Egypt Rasha Fouad Medicinal and Aromatic Plants Research Department, National Research Centre, 33 Elbouhouth St., Dokki, Giza, Egypt Saber F. Hendawy Medicinal and Aromatic Plants Research Department, National Research Centre, 33 Elbouhouth St., Dokki, Giza, Egypt Elsayed A. Omer Medicinal and Aromatic Plants Research Department, National Research Centre, 33 Elbouhouth St., Dokki, Giza, Egypt Abstract---Calendula officinalis L. is primarily cultivated as cut flowers plant and also regarded as a medicinal plant with a variety of therapeutic uses. Irrigation management results in reduction in irrigation requirements, water saving and conservation. Tryptophan has a major role in improving plant stress tolerance to environmental stresses such as water deficiency. This study investigated the response of C. officinalis cultivated under drip irrigation system to the number of irrigation times week -1 and tryptophan foliar application in two successive seasons. Three irrigation treatments (once, twice and three times week -1 ) were used as the main plots and four tryptophan treatments (0, 15, 30 and 45 mg l -1 ) were applied as subplots with three replicates. Increasing the number of irrigation times from once to twice showed the highest values of investigated growth parameters, while three times a week decreased them to lower values than those of once a week. The opposite was true for flowers production in which