EFFECTS OF LIGHT-TEMPERATURE REGIMES ON PLANT-GROWTH AND ESSENTIAL OIL YIELD OF SELECTED AROMATIC PLANTS

The effects of different light-temperature conditions on leaf growth a nd essential oil yield and oil composition of Mentha x piperita L, M s picata L, M longifolia L, M rubra L and Chamomilla recutita (L) Rausch were studied in a biotron experiment. A majority of the Mentha L spec ies exposed to a 21-3 h photoperiod, simulating conditions typical of the July environment in northern Sweden, produced significantly higher concentrations of menthol than treatments with shorter photoperiods. Night temperatures had little effects on the menthol levels under the 21 h photoperiod regime. The total yields of menthol and menthone in t he Mentha L species were significantly higher in the third to fifth le af pairs compared to the topmost leaf pair position. The different env ironmental treatments had no evident effects on leaf growth (measureme nts based on the five topmost leaf pairs). The combination of 21-3 h p hotoperiod and 25-18 degrees C thermoperiod resulted in the highest le vels of alpha-bisabolol in C recutita (L) Rausch. Also, bud or flower formation was only induced in treatments with photoperiods greater tha n or equal to 17 h.