Preliminary studies for an efficient regeneration and transformation of Carica papaya L. var. Thailand red

Different tissues of Carica papaya L., var. Thailand red, were tested for their susceptibility to be transformed by the C-58-type oncogenic Agrobacterium tumefaciens strain and sensitivity to kanamycin (Km). The efficiency of transformation and the level of Km resistance depended on the type of tissue employed. For this purpose segments of hypocotyls, cotyledons, leaves and whole zygotic embryos were cultured on modified Murashige-Skoog (MS) media. Somatic embryos (SE) were obtained only from zygotic embryos, mainly from the apical dome, cultured on MS containing half-strength salts, full-strength vitamins, 6% sucrose and 5, 10 or 15 mg/l 2,4-dicloro-phenoxyacetic acid (2,4-D). Somatic embryos were noted after 30 days in cultivation and the highest efficiency (90-95) in embryogenic response was detected on the medium with 5 mg/l 2,4-D. Anatomical studies show that SE originated either from external or internal layers. Somatic embryos in different stages of development germinated and were micropropagated on two type of media. Rooted plants were grown in the greenhouse and transferred to the field. Transformed grown plants appeared morphologically normal. Present results indicate that this system is potentially appropriate in the transformation of C. papaya with both A. tumefaciens and microprojectile mediated gene transfer procedures.