Irradiance stress and plant spacing effect on growth, biomass and quality of wild marigold (Tagetes minuta L.) - an industrial crop in western Himalaya

A study was carried out over 2 years (2009 and 2010) at the CSIR-Institute of Himalayan Bioresource Technology, Palampur, India, to investigate the effect of irradiance stress and plant spacing on growth, biomass yield, essential oil content and composition in wild marigold (Tagetes minuta L.). Four shade levels (0%, 25%, 50% and 75%) and three plant spacing (45 x 30, 45 x 45 and 60 x 45 cm) were tested as per split plot design. Heavy shading (50% and 75%) strongly reduced the total essential oil content in fresh leaves and flowers. The essential oil content of leaves, flowers and the total oil increased up to the 25% shade level and declined thereafter, with a decrease in irradiance level. Ocimene and dihydrotagetones concentration in leaf oil decreased with decrease in irradiance level; however, tagetone and ocimenone showed the reverse trend. In flower oil, ocimene decreased with an increase in shade levels. Fresh leaf, stem, flower, leaf + flower biomass, and total biomass was significantly higher in the 45 x 30 cm spacing level. Essential oil content in flowers of T. minuta grown in 25% shade at 45 x 45 and 45 x 30 cm spacing recorded significantly higher essential oil content than other treatments.