| Radiation mutation breeding is an important means to develop new varieties of crops. There are many features of radiation breeding, such as broad spectrum variation of radiation mutagenesis, high mutation rate, difficult to control in mutation trait and large random characters that an effective way of creating new germ-plasm and developing new varieties. Radiation mutation breeding in the agricultural field crops, vegetables, fruit trees and ornamental plant breeding has wide applications. In recent years, radiation breeding is developing rapidly, is being applied in a variety of plants more extensive and bringing great economic value. As an important method of radiation breeding,60Co-γ radiation has made a significant contribution to the country’s radiation breeding and has applied in a variety of agricultural crop breeding. Electron beam source as a new mutation has also some applications, but mainly concentrated in the ornamental plants, less application in the new vegetable varieties breeding. The appropriate radiation dose of radiation breeding is a difficulty problem, selecting the appropriate dose of radiation related to breeding success or failure.In this study, dry seeds and primed seeds by30%PEG (PEG-6000) of two tomato cultivars irradiated by different doses of60Co-y rays and electron-beam. We hope to determined the appropriate dose for tomato radiation breeding by the seed germination testing, seedling growth observing and physiological indicators measuring. The main results are as follows:In60Co-γ rays treatment:The inhibitory effect of60Co-y rays on germination of’1479’is much larger than ’yellow pot-cultivate’ that mainly manifested in the germination rate and germination process. Different germination status of seeds showed different sensitivity to irradiation,30%PEG primed seeds have a stronger sensitivity compared with dry seeds. Although high-dose radiation can not inhibit seeds germination completely, inhibited the growth of the seedlings significantly, mainly demonstrated by the differentiation and growth of radicle. After high-dose radiation, the survival rate of tomato seedlings declined rapidly.’Yellow pot-cultivate’is a variety that with high anti-radiation ability. According to the experimental data and previous tests, we can determine its appropriate60Co-y radiation dose should be400-600Gy, while’1479’is a more sensitive variety, its dosage should be suitable for300-500Gy.The cotyledon of tomato cultivar’1479’were irradiated by different doses of60Co-y rays. Its callus, embryogenic callus induction rate and the differentiation of embryogenic callus were affected significantly. Greater than50Gy radiation of60Co-y inhibited the formation of cotyledon callus significantly and had a significant impact on embryogenic callus formation and shoot regeneration rate, but had less impact on the root regeneration rate. According to semi-lethal dose (LD50), we have come to the appropriate60Co-y radiation dose to tomato cotyledon should be around50Gy.In electron beam treatment:The low-dose electron beam showed weak impact on germination rate of tomato seed,600Gy have a certain effect on the germination rate of ’yellow pot-cultivate’, however,’1479’showed stronger sensitivity to electron beam and began to appear low germination rate when reach500Gy. Electron beam affected the germination process significantly. After30%PEG primed seeds showed greater sensitivity and lower resistance to outside electron beam radiation than dry seeds that probably because of the different activity of various substances in different germination status. The differentiation and growth of radicle were inhibited significantly, we called it’short-fat root’, while up to600Gy.’Yellow pot-cultivate’has a stronger ability of anti-electron beam. According to the experimental data and previous tests, we can determine its appropriate electron beam radiation dose should be500Gy, while’1479’is a more sensitive variety, its dosage should be suitable for400Gy.Electron accelerator treatment had a serious impact to M1generation growth and development of seedlings. Treatment group plants grow slowly, plant height and stem diameter was significantly lower than the control group; electron beam treatment affected biomass accumulation of the seedling body; the number of lateral branches and lateral root of treatment group is much larger than the control group, and also produced a significant impact to the reproduction growth of the tomato. Seedlings subjected to radiation had a significant increase of osmoregulation substances and showed a visible change in antioxidant enzyme activity. As the dose increased, the osmoregulation substances of two varieties had a large number of accumulation, antioxidant enzyme activities also showed an upward trend. Two varieties of tomato showed different resistant ability to radiation with different seedling reactions. |
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