Fenugreek (Trigonella foenum-graecum) is an annual plant belonging to the family Fabaceae and has fodder, medicinal and spice uses, and is also used as an organic fertilizer. A total of 18 treatments including the combination of two light environments (with and without supplementary blue light), three concentrations of potassium iodate (0, 2 and 4 mg L⁻¹) and four concentrations of sodium selenate (0, 2 and 4 mg L⁻¹) were organized in a three-way factorial experiment to evaluate the growth characteristics, pigments, trigonelline and seed yield of fenugreek in a greenhouse. The application of 4 mg L⁻¹ of Se resulted in the highest carotenoid, anthocyanin, plant length, fresh weight, chlorophyll and relative water content. The fresh and dry weight of the shoot and the anthocyanin increased with the 2 h supplementation of sunlight with a blue spectrum; however, the fresh root decreased. The interaction of blue light with 0 mg L⁻¹ of Se significantly reduced the plant length. The content of trigonelline was significantly improved with the application of blue light supplementation without negatively affecting the seed yield. In general, 2 h supplementing of sunlight with blue light and feeding with 4 mg L⁻¹ of selenium and iodine are recommended to improve various traits, including trigonelline content.

Simultaneous biofortification of vegetable crops with selenium and iodine is necessary in areas where there is a lack of these two elements. The main reason for lack of selenium and iodine in humans is inadequate intake of these two elements from vegetable crops. Biofortification through various agricultural methods including artificial lighting is a pragmatic way of increasing the concentration of these elements in plants. This research was conducted as a three-factor factorial experiment arranged as completely randomized pots replicated thrice in the greenhouse during year 2022. Three levels of sodium selenate fertilizer (S1: 0, S2: 2, S3: 4 mg/l), three levels of potassium iodate (I1: 0, I2: 2, I3: 4 mg/L) and two additional blue light radiation levels (L1: radiation and L2: no blue light radiation) were applied and data was measured at two growth stages namely 40 and 80-days. The results showed that the highest (11.44 g) and the lowest (9.55 g) shoot dry weight values at the 40-day-stage were observed in the supplementary blue light and sunlight (control), respectively. Moreover,, under complementary blue light conditions, the highest and the lowest (5.85 and 3.38 mg/g leaf fresh weight) of leaf chlorophyll value at the 40-day-stage were recorded at sodium selenate 4 and 0 mg/l, respectively. The highest and the lowest (5.24 and 4.76 mg/g) fresh weight of leaf anthocyanin at the 40-day-growth stage were related to supplementary blue light and sunlight treatment (control), respectively. Under the supplementary blue light and 0 mg/l of selenium , the highest and the lowest value of shoot trigonelline (102.56 and 72.14 mg/100 g fresh weight) were obtained at 4 and 2 mg/L of iodine, respectively. Furthermore, in the same treatment, the highest and the lowest of seed trigonelline amounts (0.99 and 0.74 mg/g dry weight) corresponded with 4 and 0 mg/l of iodine, respectively.