Physical mutagenesis is an effective mutational breeding method for improving various morphological characteristics
of agricultural and medicinal crops. The objective of the conducted experiment was determining the effective dose
of gamma radiation to induce mutations in Calotropis gigantea. Well matured seeds of C. gigantea were exposed to
Gamma irradiation using “Gamma chamber 1200 Cobalt-60” research irradiator and these treatments were carried
out at the Horticultural Crop Research and Developmental Institute at Gannoruwa, Sri Lanka. Mature seeds were
subjected to seven treatments as 150Gy, 300Gy, 450Gy, 600Gy, 750Gy, 900Gy and non-irradiation (0 Gy) as a
control to study their effect on germination percentage, survival rate and growth performances of C. gigantea.
Treated seeds were arranged under shade house condition in Completely Randomized Design with four replications
and each replication contained twenty-four seeds. The mutagenic treatments were tested for lethal dose of 50% and
the dose at which 50% of the survival at four months was considered as LD50 value. Data were analyzed by
ANOVA using Minitab 17 software and compared the treatment means using Dunnett’s test at 0.05 significant level.
The study revealed that the higher dosages of gamma irradiation was significantly decreased the germination
percentage, survivability and growth performances (P<0.05). Plant survivability, number of leaves and plant height
were significantly (P<0.05) reduced with the higher dosages of 450 Gy to 900 Gy. Lethality level of gamma irradiation
for Calotropis gigantea was found as 395 Gy at maturity stage and it could be concluded that the radiation below
395 Gy should be imposed to induce mutations in Calotropis gigantea.