Oryzalin induces polyploids with superior morphology and increased levels of essential oil production in Mentha spicata L

Efficacy of oryzalin to generate novel genotypes of Mentha spicata L. with superior morphology and enhanced levels of essential oil via in vitro polyploidization was assessed. Micropropagated nodal segments were treated with oryzalin at 20, 40, and 60 mu M for 24 and 48 h. The survival rate of the nodal segments dropped significantly with the increasing concentration and duration of oryzalin. Further, the ploidy level of the survived plants was confirmed using flowcytometry and chromosome counting. A total of six polyploids (2 n = 6x = 72) and six mixoploid plants were obtained. The highest frequency of polyploids (8 %) was induced in treatment where 40 mu M oryzalin was applied for 48 h. The obtained polyploids exhibited significantly larger, thick, dark green leaves with elongated stomata compared with the control genotype. The polyploid plants also displayed higher moisture content and vigorous lateral growth. The essential oil yield of hexaploid M. spicata exhibited a 48.85 % increase, rising from 1.74 % in control to 2.59 % (v/w) in genotype P3. The major components of essential oils were carvone and limonene, which also increased significantly compared with the control genotype. The nutrient profile of the studied genotypes was influenced vastly and showed significant variations. Overall, the employed methodology using oryzalin as an antimitotic agent for polyploid induction in M. spicata was found to be effective. Despite relatively low polyploid induction frequency, the obtained polyploid genotypes demonstrated various superior agronomical traits. The genotypes obtained could serve to aid the commercial demands.