Financial support: This project was supported by the Agencia Nacional de Promoción Científica y Tecnológica (PICTO Nº 08-13164 and 08-12925), Argentina.

Keywords: genetic transformation, kanamycin, selection, sunflower.

Despite of numerous publications in sunflower genetic transformation, there is no efficient or reproducible protocol with low number of escapes. The latter would indicate that the selection method is not effective. In this work we used Km as selective agent, Agrobacterium tumefaciens EHA105 strain and a vector with the nptII gene under the nos promoter and uidA gene under 35S promoter. The response of agroinfected (A) and control (C) explants during the in vitro culture was studied and in both cases in presence or absence of Km in order to assign a differential morphologic response between transformed and non-transformed plants. The characteristics analyzed were: height, colour/aspect of the plantlets, in vitro rooting and in vitro bud-flower development. Selection was applied from the third regeneration media. Among the A plantlets two were capable of rooting, being positive by PCR, whereas the C were unable to root in presence of Km. One of them gave 6 seeds and in these plants, it was determined the presence of the transgene by PCR and GUS staining. This work shows that in Km selection, colour/aspect of shoots is not useful as selection criteria whereas rooting is an effective selection method in which no escapes were obtained.