Agrobacterium Tumefaciens-Mediated Transformation Of Spermidine Synthase Gene MdSPDS1 And In Vitro Plant Regeneration Of Citrus

Citrus (Citrus spp.) is an economically important world fruit. However, the production of citrus is limited because of heavy losses due to biotic and abiotic stress (disease) such as cold and freezing damanage; high temperature injury; drough salinity of the soli. Although great efforts have been made through traditional breeding methods, citrus breeders have had limited success owing to many problems, i.e., nucellar polyembryony (apomixis), high heterozygosity, inbreeding depression and the long juvenile period. Genetic transformation, which opened up new avenues to develop citrus cultivars with new agronomic traits, is an alternative pathway used by breeders to overcome these problems.Aimed at creating new citrus types with enhanced multiple environment stress tolerance, embryonic callus of 9 citrus varieties and epicotyl segments of 'Bingtangcheng' orange and oval kumquat were used as receptor materials for transformation of MdSPDS1 mediated by Agrobacterium tumefaciens. Meanwhile, modification was made to improve in vitro regeneration efficiency of adventitious shoot from epicotyl segments of Bingtangcheng orange, adult axillary bud and citrus thin cell layer culture. The main results are as follows:(i) Kanamycin-resistant calli of 10 cultivars (5 cultivars were PCR-positive) and 23 PCR-positive oval kumquat plantlets were obtained, respectively.(ii) An intensive study on the effect of pH value of the co-cultivation medium on the kanamycin-resistant shoot rate was investigated. The result showed that the highest kanamycin-resistant shoot rate appeared after co-cultivated on the medium with pH 5.4. Genotype is another vital important influence on the kanamycin-resistant calli rate, according to a cursory calculate, compare with 9 cultivars used in this study, the transformation is easy with the material of Hongkong kumquat, Skagg's Bonanza navel orange and Red marsh grapefruit; and difficult with the material of Tarroco blood orange, Calamondin orange and Mexican lime; Anliucheng orange, Murcott tangor and Australian...