Modulation of leaf internal volatiles and essential oil contents in patchouli [<i>Pogostemon cablin</i> (Blanco) Benth.] by application of filtered solar spectra

<i>Pogostemon cablin</i> (Blanco) Benth. is a shade-loving aromatic plant popular for its rich aromatic essential oil. Photoselective shade nets allow plants to receive filtered solar spectra which have impact on growth and metabolism; besides, these nets help plants to tolerate biotic or abiotic hazards. Here, we assess the impacts of coloured shade nets on growth and essential oil accumulation in patchouli aiming to introduce this agricultural practice for cultivation of aromatic plants in subtropical climate of eastern India. In this study, the plants were cultivated under four different coloured shade nets, <i>viz</i>. green, blue, brown and black across three seasons (monsoon, winter and summer). Significantly larger and thinner leaves under all the shade nets were observed in every season with enhanced content of photosynthetic pigments. In contrast, small and thick leaves in open field with significantly lower pigment concentration were found when cultivated in open field. A range of variations was observed in concentrations of major sesquiterpenoid, patchouli alcohol along with other terpenoids under different experimental conditions. This suggests alteration in the physiology of patchouli plant under different coloured shade nets in different seasons. Green and brown coloured shade nets in all three seasons recorded higher essential oil content and essential oil yield than the other conditions. The highest concentration of patchouli alcohol was found under blue shade net in winter. Overall, green and brown coloured shade nets were found to be most suitable for patchouli cultivation to harvest high-quality essential oil throughout the year in Indian sub-tropical regions.