Effect of different pre-treatments on seed germination of Prosopis juliflora and Dalbergia sissoo: a step towards mutation breeding

For improving the seed germination of Prosopis juliflora and Dalbergia sissoo different treatments were tested, including side cutting, abrasion, overnight soaking in boiling water, scalding in actively boiling water for 1 minute and immersion in 30%, 60% and 95% H2SO4 solution. Results showed that abrasion with sandpaper and side cutting were the most effective methods to break seed dormancy in both species, while scalding in actively boiling water for 1 minute, overnight soaking and different concentrations of H2SO4 gave low to zero seed germination. Based on the positive effects of scarification it was concluded that seed dormancy in both species was due to water impermeability of the seed coat. Mutation breeding involves the treatment of large quantities of seeds, therefore abrasion with sandpaper was the most efficient and less labour-intensive method; this method was subsequently used for determination of LD50 as it is a prerequisite in a mutation breeding program. Abrasion before irradiation had a positive effect on P. juliflora whereas it had a negative effect on D. sissoo seeds. Seeds of both species were exposed to different doses of gamma rays such as 0, 100, 200, 300, 400 and 500 Gy using a 60Co source. The LD50 for P. juliflora was 651 Gy based on the rate of seed germination indicating that P. juliflora had tolerance to irradiation and low radiosensitivity to gamma ray. A high LD50 of 1097 Gy was observed for D. sissoo, suggesting high tolerance to irradiation and very low radio sensitivity. These findings will help to initiate a mutation breeding program in both species to obtain desirable mutants with desirable characteristics such as thornless genotypes, better tree form, disease resistance and increased genetic diversity.