Articles
STEM ELONGATION AND GROWTH OF MENTHA ROTUNDIFOLIA IN VITRO AS INFLUENCED BY PHOTOPERIOD, PHOTOSYNTHETIC PHOTON FLUX, AND DIFFERENCE BETWEEN DAY AND NIGHT TEMPERATURES
Four nodal cuttings, each with two leaves, were cultured for 19 days on 0.6 x 10-4 m3 MS agar medium with no added sugar in a 3.7 x 10-4 m3 hexahedral polycarbonate box.
Each box had two holes and each hole was sealed with a round 10 mm gas permeable filter.
The average daily temperature in culture room was set the same at 23°C for all treatments, and CO2 concentration and RH were maintained at 400–500 μmol-1 and 50–70 %, respectively.
Stem and internode lengths were significantly suppressed by high PPF, and short photoperiod, especially under 0 and -9 DIF. Stem diameter, leaf area and number of leaves were significantly enhanced by long photoperiod.
Specific leaf area decreased with increasing PPF and with increasing photoperiod.
Leaf area and specific leaf area were significantly suppressed in the -9 DIF treatment.
Long photoperiod and high PPF led to an increase in the fresh and dry weights, especially those of roots, maintaining similar percent dry matter.
Under the same amount of integrated PPF, fresh and dry weights of leaf, stem, root, and whole plantlet were significantly higher under long photoperiod and low PPF than under short photoperiod and high PPF condition.
Because of suppressed root growth, T/R ratio significantly increased under short photoperiod, but was not affected by DIF. It is suggested that in micropropagation of mint plantlets under photoautotrophic conditions, a combination of high PPF, long photoperiod and small DIF to be used for plantlets with a sturdy short stem, and large DIF, low PPF and long photoperiod for plantlets with a slender long stem.