Germination of immature embryos and multiplication of Malaxis acuminata D. Don, an endangered therapeutically important orchid, by asymbiotic culture in vitro

摘要

The effect of culture conditions and developmental stages of embryos on asymbiotic germination of immature seeds of Malaxis acuminata D. Don, an endangered therapeutically important terrestrial orchid, was investigated. Immature seeds of similar to 7-8 wk after pollination (WAP) were germinated on MS medium containing sucrose (3%, w/v) and alpha-naphthalene acetic acid (NAA; 4 mu M) under diffused light condition (20 mu mol m(-2) s(-1)), where about 85% seeds germinated after 135 d of culture. The full light condition (40 mu mol m(-2) s(-1)) did not support healthy germination. The germinated seeds converted into protocorm-like bodies (PLBs) and further differentiated into young plantlets on the same germination medium. The rooted plantlets with well expanded leaves and distinct pseudobulb were achieved on MS medium containing sucrose (3%), activated charcoal (AC; 0.3%, w/v), and NAA and benzyl adenine (BA) (3 mu M each in combination), where as many as 18 shoot buds/PLBs developed per subculture. Amongst the three different organic carbon sources and two basal media tested, only sucrose supported the optimum plant growth and culture proliferation when maintained on MS medium. Incorporation of AC (0.3%) in the regeneration medim accelerated the culture proliferation and distinct pseudobulb formation. The hardened plants transferred to potting mix and maintained in the polyhouse (75% shade) before transferring to the wild, where similar to 75% transplants survived after 2 months of transfer.