Dendrobium Sonia-28 is an important ornamental orchid in the flower industry. In vitro mutagenesis by means of gamma irradiation can be used to produce economically improved mutants. Protocorm-like bodies (PLBs) of Dendrobium Sonia-28 were subjected to gamma irradiation at doses of 10 to 200 Gy gamma rays. Results showed that PLBs survival rate and weight were inversely related to the irradiation doses. In untreated PLBs, survival rate and weight were tenfold and fivefold higher as compared to

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... 00 irradiated PLBs. Results indicated that the radio sensitivity test (LD50) for the PLBs were approximately at 43 Gy. There were appreciable variations in plantlet structure and morphology relative to increase irradiation doses. Plantlets infected with low doses of gamma radiation had better development of the shoot and root as well as the foliage. SEM and TEM analysis disclosed severe surface and cell organelles damage and stomatal closure in protocorm-like bodies (PLBs) infected with the high irradiation dose. Therefore, the findings of this study have proven an efficient method of in vitro mutagenesis through gamma radiation. The results obtained in this study suggested that PLBs survival rate, growth rate percentage, morphological characteristics as well as techniques such as SEM and TEM may be used in early assessment of effectiveness and superiority of radiation dose to induce mutations. Moreover, Some RAPD markers clearly discriminated between selected and non-selected variants of Dendrobium Sonia-28, showing different banding patterns for each gamma irradiation doses.