Development of a Highly Efficient and Simple Micropropagation System for Phalaenopsis Using Elongated Protocorm-like Bodies Induced by Skotomorphogenesis under Dark Conditions

A highly efficient and simple micropropagation system for Phalaenopsis was developed using elongated protocorm-like bodies (ePLBs) obtained by skotomorphogenesis. When normal protocorm-like bodies (nPLBs) without growing point excision were cultured under different light conditions (dark: 0 mmol·m-2·s-1, low light: 2 mmol·m-2·s-1, high light: 80 mmol·m-2·s-1, of photosynthetic photon flux density respectively), PLB proliferation efficiency was higher under dark than high light and low light conditions. In addition, shoot formation percentage was lower under dark conditions (8.0%) than under low light (66.0%) and high light conditions (68.2%) and few PLBs developed shoots during culture under dark conditions. The Secondary ePLBs obtained after culturing under dark conditions were approximately twice as long as nPLBs. After acclimation under low light conditions for 2 weeks, the ePLBs were transferred to high light conditions after making a partial incision in their apical parts. Under high light conditions, a large number of secondary PLBs were obtained from ePLBs, 6 times as many as from nPLBs treated with the same partial incisions. The findings of this study showed that culturing PLBs in dark conditions suppresses shoot formation that might interfere with PLB proliferation, and that a large number of secondary PLBs could be obtained from these ePLBs compared with nPLBs after exposure to high light intensity.