Modulation of radiosensitivity with gibberellic acid (GA3) for cytogenetical, biochemical, seedling physiology and genetic variation was carried out in three chickpea (Cicer arietinum L) genotypes having different seed coat colours. Dry seeds of three genotypes namely Noor 91, Punjab 91, and C 141, were irradiated at dose level of 10,20,30,40, 50, 60, 70, 90, and 110 Kr. A part of the irradiated seeds were treated with 0.5 mM solution of GA3 for 16 hours prior to various experiments. Mitotic index decreased, while chromosomal anomalies increased with an increase of irradiation level. The chromosomal aberrations recorded were fragments, bridges, and laggards at anaphase. However, these anomalies were not observed upto 30 Kr in the three varieties. Post mutagenic application of GA3 increased the mitotic index and decreased the chromosomal anomalies and it was more pronounced at higher doses. Irradiation level of 10, 60 and 110 Kr was used to determine the effect on nucleolar volume and structure. Frequency of cells having greater nucleolar volume increased with an increase of irradiation, while the effect was reduced with the application of GA3.
Gamma irradiation decreased the fresh weight, protein, RNA and DNA contents with an increase of irradiation dosages except at lower doses where simulation as compared to control was observed. Application of GA3 modulated the radiosensitivity and fresh weight, protein, RNA and DNA contents increased at various irradiation dosages.
Peroxidase and catalase activity increased over the control upto 3rd and 5th day, respectively and then decreased for the following days at various doses of irradiation. Exogenous application of GA3 increased the catalase and peroxidase activity at various doses throughout the developmental period. IAA oxidase activity stimulated at lower doses of irradiation, while at higher doses it was decreased regularly with irradiation intensity. GA3 treatment increased this activity across various doses. Germination was inhibited regularly with an increase of gamma irradiation except at lower doses, while with GA3 treatment inhibitory effect was recorded only at higher doses of 60, 70, 90 and 110 Kr. Shoot length, root length and number of roots decreased consistently with an increase of gamma irradiation. Application of GA3 restored the growth and an increase was observed at various doses. From this study doses of 40, 50 and 60 Kr were considered as appropriate for induction of genetic variability.
Irradiated seeds at 40, 50 and 60 Kr of three genotypes along with the application of GA3 were sown at Barani Agriculture Research Institute (BARI), Chakwal. A wide range of genotypic variation was induced with gamma irradiation for all the characters like plant height, number of primary and secondary branches, pods per plant, seeds per pod, 100-seed weight, biological yield, grain yield, harvest index, days to 50% flowering and days to maturity. Application of GA3 changed the spectrum of induced variation either in positive or negative direction at various intensities of irradiation. Genotype-treatment revealed significant and highly significant interaction for all the characters under study in one or the other generation. Stimulating effect with GA3 were observed for seeds per pod, 100-seed weight, grain yield and harvest index in M2 and M3 population. It was, therefore, suggested that post mutagenic application of GA3 might be beneficial if utilized for grain yield enhancement.
Albina, xantha, chlorina and viridis chlorophyll mutants along with other morphological i.e., stem, branching, leaf, pod, seed, flowering and maturity mutants were obtained in M2 generation. Chlorophyll mutants decreased, while morphological increased with application of GA3
The results regarding correlation coefficients revealed a high magnitude of genotypic than phenotypic for most of the characters in M1, M2 and M3 generation. However, the association of grain yield with other characters changed in succeeding generations independently among the genotypes. Grain yield was positively correlated with pods per plant, seed per pod, and 100-seed weight in different populations of the three genotypes, while the association of other characters with grain yield was inconsistent. Harvest index and biological yield in variety Noor 91 had positive direct effect on grain yield in Ml, M2 and M3 population. In Punjab 91, harvest index and biological yield in Ml generation, while in M2 and M3 generation pods per plant, seeds per pod and 100-seed weight had strong positive direct effect on grain yield. In case of variety C 141, 100-seed weight and pods per plant had direct positive effect on grain yield in Ml, M2 and M3 generation. So harvest index and biological yield would be a reliable criterion in Noor 91 and pods per plant and 100-seed weight in variety Punjab 91 and C 141, in the selection of best genotypes of chickpea