Influence of exogenous tryptophan application on production and carotenoids of Calendula officinalis under drip irrigation treatments

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.