Effect of different photoperiodic regimes on growth, flowering and essential oil in Mentha species

Three major cultivated Mentha spp. (M. arvensis, M. citrata and M. cardiaca ) were grown under short-days, normal-days or long-days for 60 cycles. Subs equent to photoperiodic treatment, the plants were assessed for growth beha viour, essential oil content, oil composition and essential oil biosynthesi s. The species grew better under long-day conditions. The long-day treatmen t resulted in flowering in M. citrata, which normally does not flower under our conditions. The oil concentration and biogenesis was maximal in short- day plants. The photoperiodic treatment also affected the oil composition. The observations are discussed in relation to physiology of the oil biogene sis.