Effect of colchicine-induced polyploidy on morphological characteristics and essential oil composition of ajowan (Trachyspermum ammi L.)

Polyploidy is an amazing evolutionary event that can be used in plant breeding to improve plant material. The present study was conducted to assess the effect of in vitro-induced polyploidy on different properties of Ajowan medicinal plant. Five different concentrations of colchicine, including 0.025, 0.05, 0.1, 0.2, and 0.5% (w/v), were applied to germinating seeds of ajowan in six different durations of exposure, including 6, 12, 24, 36, and 48 h. Chromosome counting showed successful duplication of chromosome number in tetraploid plants (2n = 4x = 36) in contrast with intact diploid plants (2n = 2x = 18). DNA content duplication in induced tetraploid plants was proved through flow cytometry analysis. The highest tetraploidy induction was achieved by applying 0.05% (w/v) colchicine for 24 h with 11.53% efficiency. The tetraploid plants achieved were larger than their diploid intact plants for plant height, leaf length, stem diameter, inflorescence length, peduncle length, and seed length characteristics. The length and width of stomata were increased in induced tetraploid plants, whereas stomata density was decreased, in contrast with initial diploid plants. Gas chromatography mass spectrometry (GC/MS) analysis showed significant increases in thymol content in essential oil of tetraploid plants (69.2%) in contrast with those of diploid plants (49.67%).