Transgenic grapefruit plants obtained by Agrobacterium tumefaciens-mediated transformation

The economically important citrus crop plant, grapefruit, was genetically t ransformed, which has not been previously reported. Seedling epicotyl tissu e was infected with Agrobacterium tumefaciens carrying a T-DNA vector plasm id containing genes for the scorable marker, beta-glucuronidase (GUS) and t he selectable marker NPTII. Shoots that regenerated from epicotyl segments from nucellar seedlings in the presence of kanamycin were analyzed. Histoch emical staining verified expression of the GUS reporter gene in 43.5% of th e regenerated shoots examined; however, the majority were chimeric for GUS expression while 11.9% stained solid blue. Transgenic plants were recovered from regenerated shoots by direct rooting using a simple protocol. The pre sence of the transgene was confirmed in 25 regenerated grapefruit plants by histochemical staining, PCR and Southern hybridization.