Growth, Physiological Response, and Phytochemical Composition of Mustard Plant as Affected by Light Intensity and Deficient Irrigation

Abstract

Mustard is a medicinal plant known in various civilizations for its distinctive properties. Enhancing the production of primary and secondary metabolites in medicinal plants depends on light intensity and irrigation. This study evaluated the effects of two levels of light intensity full sun light (no shade) and 50% of sunlight (50% of shade) and four levels of irrigation (40, 60, 80, and 100% of field capacity) on the growth, physiology, and phytochemical and antioxidant activity of mustard (Brassica juncea) using a randomized complete block design with three replications. Results showed a significant increase (P ≤ 0.05) in plant height, chlorophyll pigments (ab - b - a), stem dry weight, and seed yield at 50% of light intensity. Meanwhile, the quantification of total phenolic and flavonoids content (TPC and TFC), and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) significantly increased under low irrigation levels. Irrigation at 60% increased the TPC by 80.32% compared with 100% irrigation. High TPC and DPPH activity were observed at 40% irrigation. The RSR was significantly affected by high light intensity, increasing by 68.97% under full sunlight. Growth and chlorophyll pigments were more affected by light intensity than phytochemical compounds, which were more influenced by deficient irrigation. Under 50% of sunlight, the mustard plant allocated more biomass to the shoot system than to the root. In conclusion, the increase in seed yield is linked to optimal levels of lighting.