Irradiation and preparation of carrageenan: Solid material of k-carrageenan (Sigma-Aldrich, USA) was sealed in a glass tube with atmospheric air. The samples of carrageenan were irradiated in Co-60 Gamma Chamber, GC-5000 supplied by BRIT, Mumbai, India, at a dose rate of 2.4 kGy/h. The samples were irradiated to a total dose of 250 kGy. Different aqueous concentrations of IC were finally prepared as spray treatments using double distilled water. Experimental set up and growth analyses: Authentic seeds of fennel were procured from Central Institute of Medicinal and Aromatic Plants (CIMAP), Lucknow, India. The experiment was conducted in randomized block design in earthen pots (25 cm diameter × 25 cm height) in the naturally illuminated environmental conditions in the net house of the Department of Botany, Aligarh Muslim University, Aligarh (27° 53′ N latitude, 78° 51′ E longitude, and 187.45 m altitude). Different concentrations of gamma-irradiated carrageenan solution (40, 60, 80 and 100 mg/L) were applied. Each treatment was replicated four times and each replicate-pot contained two plants. Plants were sprayed three times with IC. The first spray was carried out at 40 days after sowing (DAS), while the second and third sprays were applied after one and two weeks, respectively. Control plants were sprayed with deionized water. Performance of the crop was assessed in terms of growth attributes, physiological and biochemical parameters, essential oil yield and main components of the oil. Growth, physiological and biochemical attributes were determined at flowering stage (70 DAS).

Among various concentrations, 80 mg/L of IC gave the best results regarding yield and main components of essential oil of fennel. As compared to the control, it maximally augmented the per-plant yield of essential oil (66.3%) and the contents of main constituents of essential oil, viz. anethole (86.0%) and fenchone (7.82%) at 150 days.