EFFECTS OF LIGHT-INTENSITY AND LIGHTING DIRECTION ON THE PHOTOAUTOTROPHIC GROWTH AND MORPHOLOGY OF POTATO PLANTLETS IN-VITRO

Photoautotrophic growth and morphological characteristics of potato (S olanum tuberosum L. cv. 'Benimaru') plantlets culture in vitro with si deward lighting were compared with those cultured with conventional do wnward (overhead) lighting at four different photosynthetic photon flu x densities (PPFDs) ranging between 30 and 120 mumol m-2 s-1. The shoo t length was about 20 mm shorter in the sideward lighting treatment th an in the downward lighting treatment at each PPFD. Dry weight, fresh weight and leaf area of the plantlets cultured in vitro photoautotroph ically for 21 days in the sideward lighting treatment were similar to those in the downward lighting treatment at each PPFD. They increased with increasing PPFD to about 90 mumol m-2 s-1, then leveled off. The shoot length of the plantlets decreased with increasing PPFD in both l ighting treatments. The sideward lighting system provided higher quali ty micropropagated transplants with reduced shoot length than the down ward lighting system at each PPFD.