Foliar application of phenylalanine, tryptophan, and tyrosine in fragrant rice production: Aroma, yield, grain quality, and economic return

Phenylalanine, tryptophan, and tyrosine are amino acids that are important to the growth and development of crops. However, the application of these amino acids in fragrant rice (Oryza sativa L.) production has not been reported. The present study aimed to investigate the effects of exogenous amino acids on aroma, yield, grain quality, and economic return of fragrant rice. At the heading stage, phenylalanine, tryptophan, and tyrosine at 0.50, 1.00, and 2.00 g L−1 were foliar applied to fragrant rice plants respectively and the treatment sprayed with distilled water was taken as control. The results showed that the foliar application of these amino acids significantly increased grain yield and seed-setting rate of fragrant rice. The total return and net income of fragrant rice production increased due to amino acids and the highest or equally highest net income and benefit-cost ratio was recorded in phenylalanine treatments with 0.50 and 1.00 g L−1 and tryptophan with 1.00 g L−1. However, amino acids applied at 2.00 g L−1 significantly decreased the benefit-cost ratio. Foliar application of phenylalanine, tryptophan, and tyrosine significantly enhanced superoxide dismutase activity. Phenylalanine treatments also increased the chlorophyll content. Compared with control, phenylalanine and tryptophan treatments significantly increased the grain content of 2-acetyl-1-pyrroline (2-AP) which is the key volatile component of fragrant rice aroma. The increased 2-AP content was explained by enhanced activity of proline dehydrogenase which plays an important part in catalyzing the conversion from proline to 2-AP. In conclusion, foliar application of phenylalanine, tryptophan, and tyrosine improved yield formation and economic return of fragrant rice. Foliar application of phenylalanine and tryptophan also enhanced 2-AP biosynthesis in fragrant rice.