FACTORS INFLUENCING AGROBACTERIUM-TUMEFACIENS-MEDIATED TRANSFORMATIONAND REGENERATION OF THE SAFFLOWER CULTIVAR CENTENNIAL

The effects of co-cultivation conditions on transformation efficiency and direct shoot regeneration from seedling explants of safflower cv. 'Centennial' were examined. Agrobacterium tumefaciens strain EHA105/p3 5SGUSInt was more infective than LBA4404/pBI121 as determined by numbe rs of sectors expressing P-glucuronidase activity. Compared to nontran sformed controls, efficiency of direct shoot regeneration was markedly decreased by co-cultivation with EHA105 and the decrease exacerbated by addition of acetosyringone, indicating that a hypersensitive respon se to bacterial infection may reduce organogenetic potential. Likewise exposure of cocultivated explants to kanamycin or geneticin in select ive media reduced regeneration efficiency. Addition of 500 mg l(-1) ca rbenicillin slightly increased numbers of regenerating shoots. Transfo rmed shoots were obtained only when kanamycin selection was initiated 1 or 2 days after co-cultivation. Presence of transgenes in geneticin- resistant shoots was confirmed using polymerase chain reaction and Sou thern hybridization assays.