GUS expression in blueberry (Vaccinium spp.): factors influencing Agrobacterium-mediated gene transfer efficiency

Several factors were investigated for their influence on the transfer of an intron-containing beta-glucuronidase (GUS) gene into blueberry (Vaccinium spp.) leaf explants during the early stages of Agrobacterium-mediated gene transfer, including days of cocultivation, strain of Agrobacterium tumefaci ens? explant age and genotype. The number of GUS-expressing leaf zones and calli were counted immediately and 2 weeks after cocultivation, respectivel y, to evaluate the gene transfer process. Agrobacterium tumefaciens strain EHA105 (pEHA105/p35SGUSint) was significantly more effective for transforma tion than strain LBA4404 (pAL4404/p35SGUSint). Four days of co-cultivation with A. tumefaciens strain EHA105 yielded about 50-fold more GUS-expressing zones than 2 days of cocultivation. Significant differences among cultivar s were observed for both GUS-expressing leaf zones and calli. For some cult ivars, explant age influenced the number of GUS-expressing leaf zones and c alli. In most cases, the number of GUS-expressing calli was highest in thos e cultivars where GUS expression in the leaves was high.