Determination of lethal and mutation induction doses of gamma rays for gladiolus (Gladiolus grandifloras Hort.) genotypes

Gladiolus is a highly allogamous flower plant, but owing to the prolonged juvenile phase, asexual propagation is preferred, which acts as a barrier for the induction of natural genetic variability in gladiolus. Therefore, the induced mutagenesis could be utilized for the creation of desirable genotypes, without altering their basic agronomic features. An analysis of the optimum doses of γ radiation for the induction of fruitful mutations could be achieved in short period of time, compared with the conventional method of breeding. The objectives of this study were to perform radiosensitivity tests on various gladiolus genotypes using different doses of gamma rays and to determine the optimal dose of radiation dose for obtaining the greatest number of mutants. The present experiment was carried out during the winter-spring seasons, for the four consecutive years of 2017-18, 2018-19, 2019-20, and 2020-21. The seven genotypes of gladiolus were exposed to seven doses of gamma rays (⁶⁰Cobalt). Plants irradiated with radiation doses lower than 4.5 Kr (G₁) had greater plant survivability than the higher doses of gamma rays (≥5.0 Kr). The radiation of G₀ (0 Kr) result in highest plant survivability, while radiation dose of G₆ (6.5 Kr) resulted lowest survivability. LD₂₅ and BD₅₀ for all the genotypes were achieved except for V₅ and V₇, similarly the median lethal doses (LD₅₀) for V₃ and V₄ genotypes had been achieved. The highest flower blindness percent and percent abnormal plants were observed at G₅ and G₆ and between the 4.0 Kr (G₁) and 5.5 Kr (G₄) gamma ray doses, respectively. The flower colour mutation frequency was recorded highest in genotypes Tiger Flame at 5.0 Kr (V₇G₃), while the Flower colour mutation spectrum was identified between 4.0 Kr (G₁) to 5.5 Kr (G₄) in all the genotypes except for genotypes V₅ and V₇. For the generation of higher phenotypic variations, radiation dose between 4.0 Kr (G₁) and 5.5 Kr (G₄) were found the most prominent. Specifically the gamma rays radiation dose of 5.5 Kr (G₄) resulted in the highest flower colour mutation frequency. These isolated mutant lines will broaden the gladiolus gene pool and support future gladiolus breeding experiments.