A Sharma, Y P Sharma, A Rani, P Thakur
Valeriana jatamansi Jones ex Roxb. is a medicinally important species widely used for its sedative and tranquillising properties, which are primarily attributed to iridoid ester compounds known as valepotriates. Escalating demand has resulted in excessive harvesting of wild populations, emphasising the need to optimise cultivation practices for sustainable production. The present study evaluated the effects of varying light intensities on plant growth, photosynthetic performance, pigment content, antioxidant activity and valepotriate accumulation in V. jatamansi under field conditions. Seed-raised plants were cultivated under full sunlight and four shade levels (35 %, 50 %, 65 % and 80 % shade). Moderate shade conditions (50–65 %) significantly enhanced vegetative growth and underground biomass accumulation, with the maximum rootstock biomass recorded under 65 % shade. High-performance liquid chromatography revealed that the total valepotriates content in the roots (4.93 %) and rootstock (4.12 %) was highest under 50 % shade, with statistically comparable values under 65 % shade, resulting in a higher valepotriates yield per plant at these light intensities. In contrast, plants grown under 80 % shade exhibited the highest photosynthetic rate, stomatal conductance and chlorophyll content, indicating enhanced photosynthetic efficiency under low irradiance; however, this did not translate into increased secondary metabolite accumulation. Plants exposed to full sunlight showed elevated phenolic and flavonoid contents and greater antioxidant activity, reflecting a stress-induced metabolic response. Overall, the findings demonstrate a distinct trade-off between photosynthetic performance, growth and secondary metabolite biosynthesis and identify 50–65 % shade as the optimal light regime for maximising both the yield and medicinal quality of V. jatamansi.