Effect of phenylalanine and tryptophan on morphological and physiological characteristics in colocynth (Citrullus colocynthis L.)

The medicinal plant bitter apple belongs to Cucurbitaceae family. To study the effect of phenylalanine and tryptophan amino acids on morphological and physiological characteristics of Citrullus colocynthis L., an investigation was conducted according to a completely randomized block design with four treatments and three replications in University of Zanjan, Iran. The studied factors were consisted of different levels of phenylalanine and tryptophan (0, 0.5, 1, 2 mM). According to the results, phenylalanine and tryptophan very significantly affected on the majority of studied traits including plant length, fresh and dry weight of foliage, seed yield, weigh of 1000 seeds, chlorophyll, total phenol and flavonoid contents (p≤ 0.01). The maximum content of total phenol and flavonoid were reached to 16.94 and 7.31 mg/100 g fresh weight in the concentration of 1 mM phenylalanine compared to control with 10.72 and 4.04 mg/ 100 g fresh weight respectively.  Also, yield of fruit and antioxidant activity were affected significantly by the amino acid treatments (p≤ 0.05). The maximum fruit yield was 8930.6 kg/ha at the concentration of 0.05 mM tryptophan compared to 6344.4 kg/ha in control. In conclusion, various levels of tryptophan and phenylalanine can effectively improve morphological and physioloogical characteristics and hence production of this crop. To achieve the best performance, application of 2 mM phenylalanine for maximum yield of foliage, 1 mM of the two amino acids for phytochemical characteristics and 0.5 mM of the two amino acids for fruit yield, depending on the aim, can be recommended.