Two Vietnamese rice mutants (M2-2 and M2-4 - second generation line 2 and line 4 respectively), induced
by gamma irradiation were examined and compared to their parent (TT), and the Australian cultivar Amaroo (Am) for
salt tolerance and genomic differences. Seedlings in tissue culture provided high yields and good quality DNA, especially
with young shoots. Changes in DNA of the mutants in comparison to TT and Am were successfully assessed
using RAPD-PCR (random amplified polymorphic DNA-polymerase chain reaction) and RAMP-PCR (random amplified
microsatellite polymorphism-polymerase chain reaction) molecular marker techniques. RAMP-PCR was better
than RAPD-PCR at disclosing genetic changes between closely related individuals, and only RAMP-PCR was able to
detect polymorphic bands between the two mutants. A measure of heterozygocity and genetic differentiation, the Gstatistic
demonstrated that comparisons between Am and TT, M2-2 or M2-4 showed moderate genetic differentiation,
but comparisons between TT and M2-2 or M2-4 showed low genetic differentiation. Percentage polymorphism between
TT, M2-2, M2-4 and Am detected by RAPD-PCR were similar to those detected by RAMP-PCR (about 10%).
DNA bands that were polymorphic between the two mutant lines were sequenced, two bands mapped on numerous
chromosomes of rice, while two other bands mapped on one or two chromosomes, and these DNA bands on the
whole coded for regulatory genes. The results showed that especially RAMP-PCR is a versatile, sensitive and cost effective
method for measuring genomic differences between closely related plants.