GENETIC-TRANSFORMATION AND PLANT-REGENERATION OF WATERMELON USING AGROBACTERIUM-TUMEFACIENS

Adventitious shoots formed on the Proximal cut edges of different coty ledonary explants of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai; cvs. Sweet Gem and Gold Medal] cultured on Murashige and Skoog' s (MS) medium with 1 mgl-1 6-benzyladenine (BA). Light (16-h photoperi od, about 7 Wm-2 cool-white fluorescent lamps) was essential for shoot formation. To obtain transformed plants, cotyledonary explants of 'Sw eet Gem' were cocultured with Agrobacterium tumefaciens LBA4404, a dis armed strain harboring a binary vector pBI121 carrying the CaMV 35S pr omoter-beta-glucuronidase (GUS) gene fusion used as a reporter gene an d NOS promoter-neomycin phosphotransferase gene as a positive selectio n marker, for 48 h on MS medium with 1 mgl-1 BA and 200 muM beta-hydro xyacetosyringone. After 48 h of culture, explants were transferred to medium with 1 mgl-1 BA, 250 mgl-1 carbenicillin, and 100 mgl-1 kanamyc in and cultured in the light. Adventitious shoots formed on the explan ts after 4 weeks of culture. When subjected to GUS histochemical assay , young leaves obtained from the shoots showed a positive response at a frequency of up to 16%. Preculturing cotyledonary explants on MS med ium with 1 mgl-1 BA for 5 d enhanced the competence of the cells to be transformed by Agrobacterium Southern blot analysis confirmed that th e GUS gene was incorporated into the genomic DNA of the GUS-positive r egenerants. The transformed plants were grown to maturity.