Fig. 1 Viable seeds of G. speciosum evaluated by TTC
staining; (a) a non-red stained embryo; (b) a red stained
embryo.
Table 1 Percentage of seed germination after 30 days of
culture.
Medium Germination (%)
½ B5 96.9a
½ MS 76.5b
ND 66.7c
F-test p 6 0.01
C.V. (%) 4.3
Means followed by different letters within a column are
significantly different by DMRT.
embryos, and then the seed coats were ruptured by
the emerging of germinated embryos, so the embryo
enlargement and the papillae appeared on the one
end of protocorms (Fig. 2a). Since seed viability
was high, the effects of ½ MS and ND media on
lower seed germination were confirmed. Hence ½ B5
medium is recommended for asymbiotic germination
of G. speciosum. Moreover, asymbiotic germination
technique is much easier than symbiotic germination.
Asymbiotic seed germination of orchid seeds is an
efficient propagation method for large-scale production
of orchid plants. However, ½ B5 and ND media
have never been applied to promote seed germination
in G. speciosum before. An in-depth review on in
vitro orchid seed germination was reported by Kauth
et al15. Many protocols for in vitro seed germination,
in orchids have been described14, 16. In those reports,
seed germination and development were significantly
influenced by capsule maturity and pretreatment of
seeds, medium compositions, culture conditions, culture
methods, as well as other conditions. Some experimental
results, such as the germination percentage of
seeds of the same species on the same medium, were
inconsistent or even contradictory16.
For propagation of G. speciosum in vitro, Sopalun
et al13 reported the induction of PLBs from shoot tips
in ½ MS liquid medium without any plant regulators
(PGRs). This study showed that the seeds germinated
Fig. 2 Germination of G. speciosum seeds after 30 days of
culture: (a) on ½ B5 medium which showed the enlargement
of embryos and papillae (arrow), (b) on ND medium, and
(c) on ½ MS medium.
well on ½ B5 solidified medium but the seeds cultured
on ½ MS medium resulted in a larger protocorm
enlargement after 3 months of culture. Similar results
were obtained by Abbas et al17 who reported successful
propagation of G. scriptum by seed germination in
vitro. The best medium for germination of G. scriptum
was Knudson C medium supplemented with 30% CW
and the best medium for seedling development was
½ MS medium supplemented with 40% CW. Moreover,
Zhang et al18 reported that full strength of MS
medium contains high ionic concentration of nutrient
salts; therefore, ½ MS could adequately support rapid
production of protocorms in orchids. Thus the ½ MS
medium was suitable for PLB induction in this study.