The Effects Of⁶⁰Co-γ Radiation On Growth And Development Of Watermelon

The main characteristics of watermelon varieties bred have little breakthrough, becauseour country have not rich germplasm resources that is the material bases of breeding work ofoffer broad base of resources for watermelon breeding. Therefore, collection and research ofwatermelon germplasm resources, and through various breeding techniques to create a newwatermelon germplasm resources is particularly important for watermelon breeding work. Atpresent, the mutation breeding as the main means of breeding, vary plant genetic traits wereselected by the physical, chemical, and biological factors, and according to the breedingobjective bred good varieties.⁶⁰Co-γ radiation is used most as a induce source to introduceradiation for mutation breeding, which is because the mutations frequence may create newtypes to speed up the process of breeding that can rich watermelon germplasm resources, sothat more and more people pay attention to use⁶⁰Co-γ radiation for mutation breeding. In thisexperiment, different seeds size （large seed thousand seed weight163²80g, medium seedthousand seed weight83⁹5g, small seed thousand seed weight47⁶7g） of watermelon ofdry seeds have been exposed in the radiation of200Gy,400Gy,600Gy,800Gy,1000Gy dosesof⁶⁰Co-γ radiation and three varieties of watermelon priming seeds have been exposed in theradiation of200Gy,400Gy,600Gy doses of⁶⁰Co-γ radiation. Through determining of theeffects of dosage in seeds germination, surviving seedlings, quality of fruit photosyntheticpigment content in leaves, stomatal conductances, net photosynthetic rate, evaporation rate,mutation rate to study the biological effect of radiation dose of⁶⁰Co-γ on watermelon are asfollow.1. With the increase of radiation dose, emergence of dry watermelon seed and plant growth（cotyledon area, plant height, stem diameter, tendril long）, fruit size（fruit weight, fruit verticaland transect diameter） decreases. Dry watermelon seed average emergence rate, cotyledonarea, plant height, stem diameter, tendril long, branch number, fruit weight, net photosyntheticrate were significant difference than contrast in600Gy doses.2. Under the condition of800Gy,1000Gy, dry watermelon seed seedling survival rate whichis25.8%,36.0%is too low. Thus, radiation dose should not be exceed800Gy. Combined withradiation on watermelon after emergence, seedling growth inhibition degree and mutageniceffect determine the watermelon seeds suitable for radiation dose in the range of600Gy⁸00Gy.3. The influence of⁶⁰Co-γ radiation for different size, different genotypes of dry watermelonseed emergence situation （emergence time, seedling emergence, seedling survival rate andseedling growth, cotyledon area, plant height, stem diameter, tendril long） and fruit size （vertical and horizontal diameter, fruit weigh）is that. The order of the radiation sensitivitywith watermelon different seed size was large seed> small seed> medium seed,and the orderof the radiation sensitivity with watermelon different genotype was hybrid seed>conventionalseed.4. Under the condition of200Gy big seeds （100%）, medium （39.3%）, small seed （4.8%）cotyledon can’t develop normally and finally death, so radiation dose of priming watermelonseed should be less than200Gy.In the radiation of200Gy, the medium seed （90.0%）, smallseed （89.3%） appear plant dwarf, lobation leaf, irregular of leaf shape, higher mutation rate,so priming seed is more suitable materials to do radiation mutagenic material. Combined withradiation on priming seeds of watermelon after surviving fraction, seedling growth inhibitiondegree and mutagenic effect determine the priming seeds watermelon suitable for radiationdose around200Gy.