Micropropagation of the Thai orchid <Emphasis Type="Italic">Grammatophyllum speciosum</Emphasis> blume

Protocorm-like bodies (PLBs) were induced from shoot tips of Grammatophyllum speciosum, a Thai orchid. The highest frequency of PLBs (93%) were observed on explants incubated on 1/2-Murashige and Skoog (MS) liquid medium containing 2% (w/v) sucrose without any plant growth regulators (PGRs). Tests with different carbon sources compared to sucrose revealed that maltose promoted the highest relative growth of G. speciosum PLBs (7-fold increase), while trehalose and sucrose yielded 5-fold and 4-fold increases, respectively. In 1/2 MS liquid medium, addition of 15 mg/l of chitosan promoted a 7-fold increase in PLB growth while 25 mg/l promoted a 4-fold increase. However, the relative growth rate in solid culture was significantly lower than that in liquid culture. In addition, chitosan supplementation in solid medium promoted shoot formation but not rooting. Plantlet regeneration was induced using a combination of NAA and BA supplementation in 1/2 MS solid medium with optimum induction shoot and root formation at 2.0 mg/l NAA and 1.0 mg/l BA. Using this protocol, approximately 8 months was required to obtain a hundred plantlets from one shoot tip. The plantlets showed no changes in ploidy when tested by flow cytometry.