The introduction of binary plasmids intoAgrobacteriumhosts forAgrobacterium-mediated transformation of plants is most readily achieved by electroporation. However, occasionally, no transformed colonies are recovered and the transformation program is delayed. Poor transformation rates are commonly associated with particular combinations ofAgrobacteriumstrains and plasmid-selection markers. In order to avoid this problem, it is important for the bacteria to have a highly competent status for reception of plasmid DNA. It is also important to optimize the level of antibiotic for the selection of transformed colonies. In this article, we demonstrate that transformation competence is strongly related to the phase of growth at which a bacterial culture is prepared for electroporation, and we describe a simple procedure that allows the level of transformation-competent cells to be maximized. We have observed that there is significant variation between transformedAgrobacteriumstrains in the levels of antibiotic tolerance; we define the antibiotic levels that are appropriate for selection of threeArgobacterium tumefaciens(EHA101, LBA4404, C58) and twoArgobacterium rhizogenes(LBA9402, Ar2626) strains, transformed with three alternative resistance markers (spectinomycinres , kanamycinres , and gentamycinres ).
