Study Genetic Variation Of Majia Pomelo And Citrus Paradisi ’Grapefruit’ Lrradiated By ⁶⁰Co-γ

As the largest fruit in China,citrus has extremely high economic value.Majia pomelo is a distinctive and high-quality local citrus variety in Guangfeng County,Jiangxi Province,China,which has great popularization value.However,its unstable character and single variety structure restrict its development,which is of great significance for germplas m innovation of Majia pomelo.As an imported variety,Citrus paradisi‘Grapefruit’is very popular among growers and consumers because of its premature delivery,high and stable yield,sweet and juicy pulp.However,its fruit is multi-seeded,and the number of single fruit seeds can reach more than 30,which affects consumers’consumption.Therefore,new germplasm of Citrus paradisi‘Grapefruit’with no seeds or few seeds needs to be created urgently.Therefore,it is of great significance to innovate the germplasm of Majia pomelo and Citrus paradisi‘Grapefruit’for the development of citrus industry and the renewal of germplasm.Radiation mutation breeding is an important way to create new fruit germplasm,which has the advantages of short breeding time and wide mutation range.⁶⁰Co-γradiation source is widely used in the field of radiation mutation breeding,and it is a high-quality radiation source.In this study,the branches of Majia pomelo and Citrus paradisi‘Grapefruit’were irradiated with different gradient doses by ⁶⁰Co-γradiation source,and the suitable radiation dose range of them was obtained by counting the surviva l rate and phenotype of grafted plants.Mutant plants were screened by amplified fragment length polymorphism markers（AFLP molecular markers）and fruit quality analysis,and the strains with possible excel ent mutations were obtained,so as to provide some theoretical support for the innovation of citrus germplasm and radiation mutation breeding in China.The specific research results are as follows:（1）The steps of AFLP reaction system were simplified and optimized.This experiment simplifies the optimization steps of AFLP system.The key links such as enzyme digestion system,dilution multiple of pre-amplification and selective amplification were optimized,and the optimal conditions were obtained,namely,enzyme digestion DNA template 800 ng,37℃for 3 hours;The optimal dilut io n multiples of ligation and preamplification products are 5 and 20 times respectively.It provides a quick and simple method for the optimization of AFLP marker system.（2）The optimum radiation dose of Majia grapefruit and Citrus paradisi‘Grapefruit’ was obtained.The survival rate of radiation grafted plants of Majiayue and Grapefruit with Tail-tail decreased with the increase of radiation dose,and the plants mainly showed the phenomena of missing,forking,curling and weakened growth potential.The leaves of Majiayue showed a high leaf deformity rate.Taking the survival rate of radiation grafted plants of Majiayue and Grapefruit with Tail-tail as the evaluation index,the semi-lethal doses were about 163Gy and 55 Gy,respectively.（3）Genetic variation analysis of irradiated plants of Majia grapefruit and Citrus paradisi‘Grapefruit’Twenty-three pairs of primers were used to mark 81 survival plants of grapefruit s grafted by radiation.A total of 4 pairs of primers identified 5 plants with specific bands,and the amplified bands were clear,with the size of specific bands ranging from 60 to320 bp.By analyzing the fruits of the fruit-bearing plants in the first year,three plants with few seeds were obtained,namely,No.6,No.85 and No.91,with J9 seeds,J7 seeds and J9 seeds respectively,which was much lower than that of the control,about 30seeds per fruit.Because it is the result of the first year,further observation is needed.Besides,26 pairs of primers were used to mark 126 surviving plants of Majia pomelo by radiation grafting.A total of 23 plants were marked with specific bands,and the length of specific bands was between 65 and 400 bp.Among them,5 plants detected more differential bands,namely,plants M47,M60,M5,M50 and M7,and the marked differential bands were 13,11,9,10 and 6,and there is no obvious phenotypic difference in plants,which needs further observation.