Plant regeneration through direct shoot bud formation from leaf cultures of Paphiopedilum orchids

Abstract

Leaf explants of Paphiopedilum phiIippinense hybrids (hybrid PH59 and PH60) directly formed adventitious shoots from wound regions within 1 month, when cultured on modified Murashige and Skoog medium (1/2-strength macro- and full-strength micro-elements) free of plant growth regulator in darkness. The combinations of 2,4-dichlorophenoxyacetic acid ((2,4-D) acid (0, 4.52 and 45.25 μM) and 1-phenyl-3-(1,2,3-thiadiazol-5-yl)-urea (TDZ) (0, 0.45, 4.54 and 22.71 μM) were used to test their effects on direct shoot bud formation from two types of explants (1.5-cm long intact leaf explants and 0.5-cm long leaf segment explants). In hybrid PH59, 4.54 μM TDZ increased mean numbers of shoots per explant with leaf segment explants. In hybrid PH60, 4.52 μM 2,4-D plus 0.45 μM TDZ promoted direct shoot bud formation from leaf segment explants. In addition, three treatments (4.52 μM 2,4-D, 22.71 μM TDZ, 4.52 μM 2,4-D plus 4.54 μM TDZ) gave a higher response than control on mean numbers of shoots per explant with intact leaf explants. Healthy plantlets each with one to three roots were obtained from leaf-derived shoots after transfer onto a hormone-free medium for 22 months. These plantlets were acclimatized in a greenhouse and grew well with 100% survival rate.