Creation Of Citrus Mutant Through ⁶⁰Co Radiation

Radiation-induced mutation breeding has been an effective method for creating new fruit tree germplasms, which can greatly improve the mutation frequency of fruit tree genes and generate small quantities of mutants without changing the superb characteristics already existed. This is something beyond the achieve of traditional breeding methods. It will tremendously reduce the frequency of chimerism when radiation-induced breeding combines with in vitro culture, which is effective to select mutants form a large number of groups in limited space. The combined method can improve the selection and identification efficiency of new germplasm. In this experiment, ⁶⁰Coγ-ray is used to radiate scion and callus from Valencia and Jiangxi Seedless Ponkan. Here are the conclusions:1. The proper radiation dose of Valencia and Jiangxi Seedless Ponkan is about 45Gy and dose rate is 1.0Gy/min. After radiation, six Ponkan mutant were obtained, which exhibited pronounced variation in branch and leaf phynotype: lack of carved leaf margin,enlarged leaf size, enlarged opening angle of the branches in four mutants, decreased leaf index in five mutants.2. Six pairs of primers E01-MC01, E01-MC02, E01-MC03, E01-MC04, E01-MC05, E01-MC06 were used to analyze the genetic variation of the six Ponkan mutants. Results showed that: every pair of primers can detect the difference between the control and the mutants. The different lanes were 4, 3,4, 6, 7, 3.3. ⁶⁰Co radiation has effects on the growth and development of Valencia and Ponkan embryogenic calli. In Valencia, the growth rate and somatic embryogenesis frequency of the calli increased first, then decreased as the radiation dose increased continuously. The growth rate in Valencia reached 140% at the radiation dose 60Gy, but decreased to 54.8% at 90Gy, 38.8% at 120Gy. After 15 days' radiation at 60Gy, 72 embryoid per gram occurred, which was much higher than the control; after one month's radiation, the embryogenesis frequency was 589.3 per gram, which was similar to the control. Meanwhile, there was few embryoids occurred after radiation at 90Gy and 120Gy for 15 days; but after one month, the induced embryogenesis frequency were 300.3/g and 57.0/g respectively. The growth rate and somatic embryogenesis frequency of the calli in Ponkan displayed contrary tendency with the radiation dose. Regenerated buds after radiation was very difficult to generate roots. Most of buds were not capable of generate new roots. In vitro micro-grafting and bud grafting in greenhouse were used in this study to improve the survival rate of buds, and the survival rate were 24% and 35% respectively.4. Regenerated embryo of both materials were almost malformed. Five kinds of media were used to cultivate the regenerated embryo. The medium (1/2MT+1 .0mg/LBA+ 0.5mg/LKT+0.1mg/LIAA +40g/Lsucrose+7g/Lagar, pH5.8) had more buds than the rest of media after 40 days' cultivation and the leaves of the regenerated buds were normal in morphology with healthy growth.