Effect of Arginine, Proline, and Glutamine Amino Acids on Morphological and Physiological Traits of Two African Marigold (Tagetes erecta L.) Cultivars

In addition to its ornamental and medicinal applications, marigold is considered an edible flower, too. To produce marigold with safe and non-chemical methods, a factorial experiment was conducted based on a completely randomized design with three replications and 20 treatments. The experimental treatments included two cultivars of marigold (‘Yellow’ and ‘Orange’) and three amino acids including arginine, glutamine, and proline at three levels (100, 500, and 1000 µM), as well as distilled water as the control treatment. The results showed that amino acids had positive effects on the recorded traits. The treatment of 100 µM arginine outperformed other treatments in increasing leaf number, flower diameter, shoot fresh weight, and shoot dry matter, reducing electrolyte leakage, and improving catalase activity in cv. ‘Orange’. In cv. ‘Yellow’, the highest leaf number, shoot fresh weight and root dry matter, the lowest polyphenol oxidase activity, the lowest electrolyte leakage, and the highest catalase activity were related to the treatment of 1000 µM proline. The highest total phenol was obtained from 100 µM arginine in two cultivar. With the application of amino acids, flavonoids were increased in both cultivars versus the control. Therefore, it is recommended to apply amino acids, especially arginine (100 µM) and proline (1000 µM), to produce marigolds ‘Orange’ and ‘Yellow’ in an organic way, respectively.