Increasing characteristic variations in Dendrobium orchids through acute irradiation
2005
Sakinah Ariffin | Nazir Basiran
Hybridization or cross-pollination in orchid breeding has proven to be very reliable technique for the production of a wide range of successful cultivars with attractive combinations of spray length, bud number, flower colour and form, vase life, fragrance, seasonality, and compactness. Inherently, however, it is limited by the availability of desirable genotypes and sexual compatibility of genetic sources. This report describes how mutagenesis may be used to create variations in the orchid to overcome these limitations. Mature seeds from self-pollinated Dendrobium "Sonia" were germinated and cultured in vitri on Murashige and Skoog (MS)medium, incubated at 26C under 12 h photoperiod until protocorms were formed. The protocorms were then irradiated at an acute dose of 35 Gy with gamma rays using the Gamma Cell (GC4000A) at MINT. After four periodic subcultures, the irradiated protocorms were allowed to regenerate into whole seedlings, transferred into pots and grown to maturity until flowering. Selection for induced mutants was based on variations in flower colour and form. Colour grading was based on the Royal Horticultural Society of London (RHS) colour chart. Flower size was determined by horizontal and vertical measurements of fully opened flowers. Numerous combinations of colour and shape variations in the petals, sepals and labella were observed. Single characteristics changes were also observed. One mutant for example, has totally white flowers but with similar flower shape to the control. Most mutants show a wide range of purple shades. The different colour variations are expressed as whole or in gradual distribution of intensity from pale to darker shade in petals or sepals. Intensity and uniformity of pigment distribution patterns may also vary in a single flower, resulting in coloured patches. Flower size of mutants can be 20% larger or up to 30% smaller than the control. One mutant produced a slight fragrance. These results provide a complementary method for orchid improvement.
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