Foliar Application of Chitosan and Brassinosteroids on Glutinous Rice (‘RD6’): Alteration in Growth, Agronomic Trait, Antioxidant Capacity, Elemental Composition and Aroma Compound, 2-Acetyl-1-Pyrroline (2AP) in Rice Grain

Abstract

The ‘RD6’ glutinous rice (Oryza sativa L.), developed from the popular aromatic rice ‘KDML105’ through gamma irradiation, is a key economic cultivar widely consumed in Thailand and exported throughout Asia. However, cultivation of the ‘RD6’ faces challenges due to its low grain yield and growth performance. The objective of this study was to use biostimulant chitosan and brassinosteroids to promote growth performance, nutrition, and yield of the ‘RD6’ rice. Chitosan (2.5, 5.0, 7.5, and 10.0 mg L-1) and brassinosteroids (0.00005, 0.0005, 0.001, and 0.002 mg L-1) were sprayed twice at 40-and 75-d-old rice plants in paddy fields. The results demonstrated that foliar spraying with 7.5 mg L-1 chitosan can promote leaf growth of ‘RD6’ and improve grain yield by 24% as compared with the control. More pronounced effects were observed with 0.002 mg L-1 brassinosteroid, improving not only growth but also ‘RD6’ yield by 41.8% compared to the control. Moreover, 0.002 mg L-1 brassinosteroids can enhance antioxidant capacities (total phenolic contents), elemental K and Ca contents, and the aroma compound 2-acetyl-1-pyrroline (2AP) contents in the rice grains. Furthermore, the use of 0.002 mg L-1 brassinosteroids proved to be a financially sound investment, yielding superior net returns and an advantageous benefit-cost ratio compared with 7.5 mg L-1 chitosan. Therefore, the use of exogenous brassinosteroids on glutinous rice in this study offers promising advantages for promoting the growth and physiological performance of rice plants.