Detection of DNA Instability Induced from Tissue Culture and Irradiation in Oryza sativa L. by RAPD Analysis

As a consequence of tissue culture of rice, RAPD analysis was peformed to determine whether extended culture periods as undifferentiated calli affected the subsequent genetic constancy, and whether any resulting DNA rearrangements could be detected between sibling plants produced from the same callus. Somaclonal variation was induced at the initial stage of tissue culture and it increased with the length of culture maintenance. Of the 192 total bands, the number of polymorphic bands was 22 (11.5%), 33 (17.2%), and 49 (25.5%) in the callus of 1,3, and 6 months culture, respectively. A significantly higher level of genotypic polymorphisms between regenerants from two different somaclones was also detected, although all the regenerants were derived from a single genotype. In comparison of DNA polymorphisms between regenerants from non-irradiated and from irradiated calli, a scope of variation spectrum by gamma ray irradiation was larger than that by tissue culture. Consideration must be given to this genomic variation where attempts are to be made to use desirable somaclonal variants for plant breeding purpose and in genetic engineering program.