Hexaploidy induction improves morphological, physiological and phytochemical characteristics of mojito mint (Mentha × villosa)

Abstract

Mints are cultivated worldwide as annual herbs or perennial garden plants for their aromatic and therapeutic characteristics and they are sought after by a vast number of food, confectionery, pharmaceutical, and sanitation industries. The aim of this study was to investigate the possibility of polyploidizaion in the Iranian mint genotypes to improve the morpho-physiological traits and enhance the essential oil content. Different concentrations of colchicine (0, 0.0125, 0.025 and 0.05%) and soaking times of rhizomes (3, 6 and 9 h) and three mint genotypes including peppermint (M. × piperita ‘BLACK’, 2n = 6x = 72), mojito mint (M. × villosa, 2n = 3x = 36) and pineapple (M. suaveolens, 2n = 2x = 24) were studied in a factorial experiment design with three replications. The survival rate, mixoploidy and chromosome doubling percentage of plants were checked 2 months and 24 months after induction of treatments. The highest survival rate (90.90%) and mixoploidy (11.11%) were found after two months in M. × piperita ‘Black’ and M. × villosa accessions, respectively. The only and highest rate of polyploidization (15.27%) was observed after two months in M. × villosa (2n = 6x = 72) using 0.05% colchicine for 9 h, which after 24 months some mixoploidy conversion to higher ploidy level increased it to 18.05%. It demonstrated sturdy, thick, dark green leaves with greater stomata size and guard cells’ chloroplast number and lower stomata density. Essential oil yield of hexaploid mojito mint showed 64% increase, from 0.87% (w/w) up to 1.43%. The phytochemicals, α-pinene, sabinene, limonene, menthofuran, and borneol were newly synthesized in the induced hexaploid mojito mint, while 1,8-cineole and pulegone production indicated 53% and 84% increase, respectively. Comparison of the main essential oil constituents of triploid and hexaploid M. × villosa showed a great variation in 1,8-cineole (18.5–28.4%), menthofuran (0–28.51%), neomenthol (22.7–0%), and pulegone (10.8- 20.1%), respectively. These improved characteristics suggest a valuable variety of mojito mint for commercial production.