Creation Of Poncirus Trifoliate Mutant Through ⁶⁰Coγ Radiation

Trifoliate orange [Poncirus trifoliate (L.) Raf.] is the most important citrus rootstock in China. However, it has incompatibility, low salt tolerance, susceptible exocortis and Huanglongbing disease, those weaknesses have become a prominent problem of restricting the citrus yield and quality improvement. Radiation-indueed mutation 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 achieve of traditional breeding methods. In this study, seeds of Poncirus trifoliate were used as the experimental materials. They were subjected to 60Co gamma rays irradiation treatments. Physiological mutation effects in terms of seed emergence, seedling growth and detected the proline content under drought stress were studied under different doses. These mutant seedlings screened at early stage were confirmed by the molecular using SSR, ISSR and SRAP markers. The specific mark straps by SRAP were reeovered and sequenced. The main results were as follows:(1) Effects of 60Co gamma rays on Poncirus trifoliate seeds were obvious, the seeds gerimination can significantly be promoted by low irradiation dose(30-60Gy), but inhibited by high irradiation dose. The average seeding height that irradiated by different dose of 60Co y-rays was not significance. Compare with CK, there was much difference among the leaves, thorns and plant types of Poncirus trifoliata that irradiated by 120Gy dose. It was found that effects of 120Gy on all above mentioned parameters were satisfactory to generate the variation and selection of plant materials for mutation breeding. Thus we concluded that 120 Gy was an appropriate dose of 60Co y-rays for Poncirus trifoliata seed mutation breeding.(2)Based on the phenotypic variation of 120Gy dose were screened the 100 seedlings proline content in Poncirus trifoliata leaves were measured for 20 days after drought stress, the content of proline in seedlings that irradiated by 120Gy changed from 358.16μg/g to 1372.96μg/g.(3) Selected after the self repair phenotype variation but still can induced plant normal growth and proline content in the top of the 50 Poncirus trifoliate seedings from the early screening. The essdings were amplified by PCR using 20 pairs of SSR,100 ISSR and 88 SRAP primer pairs. SSR markers failed to mark the specific bands. ISSR and SRAP were detected 34 strains of plant polymorphism of different degrees of difference with the control.(4) No thorns on the plant parts were amplified using 88 pairs of SRAP primers, screened 6 primers amplified 13 specific straps, the straps were were recovered, cloned and sequenced, got a number of different length fragments. The cloned fragments could found their higher homology sequences by proceeding Blast comparing Huazhong Agricultural University announced in sweet orange gene library, in order to suppose their protein function.