Ionizing radiations as the mutagenic agent are tools that may have specific application in plant breeding even if they ate not expected to replace conventional techniques bait rather to be supplement to regular breeding pattern today. Research on the development of better mutagenic treatment is still in progress and the method is not yet known which of a number of possible procedures is best to follow. The most efficient use of ionizing radiation in the production of new plant forms requires a through understanding of plant radiosensitivity, and familiarity with those problems will help greatly to these engaged in radiation breeding and mutation experiments. The studies of radiosensitivity on Raphams sativus and Brassica pekineusin have initiated since 1960, like the works done on the other Korean native plants or species, by author at Brookhaven National Laboratory in U.S.A., and now, it is the first example in this kind of research conducted in Korea.
Both Raphanus sativus (Oriental radish) and Brassica pekinensis (Chinese cabbage) are the most outstanding and important vegetable kinds in this country. Many of the varieties are satisfactory improved by conventional breeding methods, and yet there are quite number of posibilities to be replaced by new mutagine with the use of radiation techniques, however, their response to radiation and the radiosensitivity has not been previousely investigated.
Nine varieties from the both kind of plant material and more than seven thousand of seeds and seedlings were irradiated by X-ray, γ-ray and thermal neutron at several different doses, and a part of plant samples were transplanted or exposured at the gamma field to observe their responses to acute car chronic exposure by dose rate through-out growing season.
Careful observations and analysis on the ten different subject of investigation as following sere made in the lab, or at fields for the comparisons of characteristics of radiosensitivity and some necessary biological effects by the treatments.
(1) By levels of water content.
(2) By kinds of radiation source.
(3) By gamma-ray and thermal neutron.
(4) By dosages of irradiation.
(5) By varieties and kinds of plant.
(6) By growth of stages.
(7) By doses of acute irradiation.
(8) By dose rate of chronic exposure.
(9) By chromosome aberrations.
(10) By mutations induction.
Through the experiments certain favourable facts were investigated and summarized in below.
(1) Remarkable differences were recognized by the levels of water content in seeds, and seedlings at the time of exposure.
(2) Raphanus sativus and Brassica pekinensis were classified as the most tolerant plant, and LD-50 by acute X- and γ-ray is about 60 kr. for Raphanus sativus and about 50 kr. for Brassica pekinensis, LD-50 by chronic exposure is about 3,000 r/d to 2,500 r/d.
(3) No significant differences between X-ray and γ-ray, but more abnormalities were found by thermal neutron treatment under reasonable dosage condition.
(4) Seedlings were two times more sensitive than seeds, and acute irradiation dosages were respectable to 3 hours thermal nuetron exposure at the unit of 10×10^(12)/sec/㎤.
(5) Practically same biological effects were observed between the kinds end among the varieties used.
(6) Enhanced or stimulated growth was checked out at the acute dose 10 kr. for the seed of Raphanus, and 10 kr. for Brassica, and less than 5 kr. for seedling treatment.
(7) Severe growth inhibitions or damages were shown by the increased dosage or dose rate, but reasonable limitation of dosage or dose rate for the purposes of general mutation experiment was expected lower than 40 kr. and 3,000r/d in both plant materials.
(8) Maximum dose for the survival of the used materials seemed somewhat up to 100 kr. in acute, and 5 kr/d in chronic exposure.
(9) Promising chromosome aberration was found in lower dosages and severe irregularities were observed at higher dosages. Some characteristic cytological effects by dosages were understood
(10) Many ecological variations and some profitable somatic mutations with the relationship to breeding practice were observed, and the large sources of ionizing radiation in breeding research is realized to possible for many practical field of application.
In conclusion, general radiosensitivity and effects of radiations in these plant kind and species are understood and practical, evaluation of the efficiency of mutation induction ire reviewed. The feasibility of the general concept of the application of radiation for the useful mutation production upon these plants and species or their relatives are became fairly predictive and advisable.
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