Subject: Re: Orchid somatic embryogenesis 
From: Agricell@AOL.COM 
Date: Wed, 3 May 2000 12:15:45 EDT 
Reply-To: Plant Tissue Culture <PLANT-TC@TC.UMN.EDU> 
Sender: Plant Tissue Culture <PLANT-TC@TC.UMN.EDU> 

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The following article appeared in the Feb. 2000 issue of Agricell Report

Ed Herman, Editor
Agricell Report

Micropropagation of Orchids from Stem and Leaf Tissues

In micropropagating endangered orchid species, repeated excision of 
shoot meristems may destroy the mother plant. It is therefore desirable 
to use other plant tissues as a source of explants. At the University of 
North Bengal, B. Kanjilal and coworkers have developed a stem disc 
culture technique for micropropagating the endangered orchid Dendrobium 
moschatum (Current Science 77(4):497-500, 1999).
Kanjilal et al. prepared transverse stem sections of 6 to 8-week-old in
vitro-raised seedlings of D. moschatum by cutting the stem with a sharp,
sterile surgical blade. The sections were cultured in Knudson C liquid 
medium supplemented with 15% coconut milk, 2 mg/liter NAA and 3 mg/liter 
BAP. Within six weeks, 13-14 protocorm-like bodies (PLBs) were produced 
on each explant with 92% of the explants surviving. The PLBs, which were 
green and healthy, were separated and subcultured. After 10-12 additional 
weeks of culture, the regenerated plantlets were removed, transferred to 
ex vitro conditions in pots, and acclimated under high humidity for two 
weeks. Most of the in vitro-grown roots died, but the plantlets were 
successfully rerooted by adding NAA to the potting mixture. Hardened 
plants with new roots showed a 48% survival rate upon transfer to the 
field.
The authors cite the following advantages of using stem sections of in
vitro-raised seedlings as explant sources: (1) the easy availablity of
explants without damaging the parent plant and (2) the availablity of
"aseptic" explants which minimizes contamination. They state, "The thin
section liquid culture method . . . is a highly efficient method for 
rapid micropropagation of . . . D. moschatum."

Academica Sinica scientists J.T. Chen, C. Chang and W.C. Chang report 
that, when cultured on a Gelrite-solidified half-strength Murashige-Skoog 
medium containing thidiazuron at a concentration of 0.3-1.0 mg/liter, 
explants derived from young leaves of Oncidium Gower Ramsey orchids 
produce clusters of somatic embryos directly from epidermal and mesophyll 
cells of leaf tips and wound sufaces without intervening callus formation 
(Plant Cell Reports 19(2):143-149, 1999). These embryos, which are 
produced within one month, generate additional embryos and develop into 
plantlets on the same culture medium. Chen et al. state that "further 
modification of the protocol for plant formation could be useful for the 
mass propagation and transformation of selected elite lines."

For further information:
B. Kanjilal, Molec. Cytogenetics & T.C. Lab., Dept. of Bot., Univ. of N.
Bengal, W. Bengal-734 430, India.

W.C. Chang, Inst. of Bot., Acad. Sinica, Taipei, Taiwan 115, Rep. of China.
Fax: 886 2 2782 7954. E-mail: wcchang@wcc.sinica.edu.tw