In this study the effect of Agrobacterium tumefaciens genotype of two strains AGL1 and LBA4404 was investigated in regard to the propensity for backbone integration during the transformation of potato for blight tolerance conferred by the resistant to blight (RB) gene carried by the vector pCLD04541. A PCR based walking approach was employed to identify left and right backbone sequences as well as for selected genes carried on the plasmid backbone. It was found that adjacent to the left border insertion site, the integration of backbone sequence was greater for AGL1 than for LBA4404; however, the opposite was observed with regards to the right border T-DNA junction. Considering both T-DNA borders LBA4404 was found to have a two fold greater integration potential for backbone than the AGL1. The possibility of only backbone integration in T-DNA negative plants was also investigated with the average rate of integration between the two strains calculated at 4.2% with LBA4404 recording a three fold greater occurrence of backbone integration than AGLI. In summary, evidence of Agrobacterium genotype dependency showed that LBA4404 has greater potential to integrate non-T-DNA vector sequence than AGLI and this should be taken into account when utilising the listed A. tumefaciens genotypes in generating transgenic potato. Additionally, the application of a PCR and primer walking, system proved to be reliable and allows for fine detailed studies of backbone sequence integration of transgenic plant. (C) 2008, The Society for Biotechnology, Japan. All rights reserved.