Effect of proton ion and gamma-ray irradiation on radiosensitivity of M1 seedlings in Brassica napus

This experiment was carried out to increase the cultivation area of rape (Brassica napus) and develop this plant as a biodiesel so dry seeds of 3 cultivars, 'Naehan', 'Hanla', and 'Tammi' were irradiated with proton ion and gamma-ray at range of 0 to 2,000 Gy and then radiosensitivity of M, generation were investigated. The germination rate were more than 95.3% regardless of radiation source, dosage and cultivar and emergence rate at 6 days after sowing were decreased by increasing dosage but those of 12 days as more than 91.7% were similar all together. Survival rate in 1,000 Gy and below at 7 weeks after sowing were similar but remarkably reduced 38.1 similar to 84.1% in 1,500 Gy and 2,000 Gy. The length and area of cotyledon, and hypocotyl length in all 3 cultivars were badly reduced with high significancy by increasing dosage of proton ion and gamma-ray irradiation and sensitive responses were showed in order of 'Naehan' 'Hanla', and 'Tammi'. On the other hand, there was hormesis that the length and area of cotyledon were more increased at 100 similar to 200 Gy in the proton ion than control in 'Tammi'. Chlorophyll content, number of true leaves and leaf area at I month after sowing were decreased by increasing radiation dosage regardless of radiation source so had high significancy. As the cotyledons at I month after sowing almost showed chlorosis in more than 800 Gy and chlorosis was especially serious in "Tammi'. The number of true leaves was about 2.3 in control and the low level of dosage but cotyledon didn't grow in the high level dosage of 1,500 Gy and over. And the dosage in which leaf area was reduced to 50% compared to that of control were 800 Gy in 'Nachan' and 1,500 Gy in 'Tammi' and 'Hanla' by proton ion and 400 Gy in 'Tammi', 1,500 Gy both 'Naehan' and 'Hanla' by gamma-ray. The fresh weight of top land than root was more sensitive so dosage in which fresh weight reduced to 50% compared to that of control were 600 Gy in 'Naehan' and 1,000 Gy both 'Tammi' and 'Hanla'. As the results, growth of seedling decreased over 50% in more than 1,000 Gy with high sensitivity to radiation and so it was appeared that proper dosage for mutation breeding in rape was 1,000 Gy and below.