Effect of L-phenylalanine foliar application on the growth, morphophysiological and phytochemical characteristics of red or chili pepper (Capsicum anuum) under different irrigation treatments

The aim of this study was to evaluate the effect of L-phenylalanine foliar application on morpho-physiological and phytochemical properties of red pepper under different irrigation treatments (type and amount) in the filed experimental at Goldaru Herbal Pharmaceutical Company, Isfahan as a split-split plot experimental in the randomized complete block design (RCBD) in 2018. Experimental factors included: moisture conditions (optimum and reduced irrigation), irrigation methods (drip and flood irrigation) and different levels of the foliar application (negative control; positive control or water as solvent; L-phenylalanine at 2000 and 4000 ppm). The results indicated that the highest the plant height was related to the application of 2000 ppm phenylalanine optimum irrigation (69.3 cm), the highest values of the fresh and dry fruit weights were related to 2000 ppm L-phenylalanine × reduced irrigation × drip irrigation (6.60 g/m2) and L-phenylalanine (at 2000 ppm) × optimum and reduced irrigation × drip irrigation (2.18 g/m2), respectively. Results of the biochemical traits showed that the highest degree of intensity was under L-phenylalanine (at 2000 ppm) × reduced irrigation × flood irrigation (449 g/m2). In addition, the maximum values of vitamin C and total phenol were related to the water foliar application × optimum and reduced irrigation conditions (0.82 and 0.72 mg/g dry weight) and the water foliar application × reduced irrigation × drip irrigation (2.15 mg GAE/ g dry weight), respectively. In general, the results of this study showed the negative effect of drought stress or reduced irrigation on the growth traits of red pepper, however, reduced irrigation enhanced the degree of intensity, vitamin C and total phenol. In conclusion, the foliar application of L-phenylalanine (at 2000 ppm) could improve the quality and reduced the negative effects reduced irrigation on the growth and yield of red pepper under arid and semiarid climate.