Abstract

Sweet potato is a major world crop and its behavior under in vitro culture is genotype dependent. We studied several factors infuencing the regeneration and transformation effciency of two recalcitrant cultivars: Jewel and CEMSA 78354. Growth regulators, explant preparation and removal of apical dominance were evaluated in order to optimize the regeneration steps. At the same time, the infuence of environmental conditions for the interaction between Agrobacterium tumefaciens and leaves were evaluated to obtain higher transformation effciencies. For Jewel, the best results were obtained when intact leaf explants were cultivated on MS medium supplemented with 0.5 mgL -1 indol-3-acetic acid for four weeks (Regeneration frequency, RF=2.02). However, for CEMSA 78354 the best results were obtained by culturing leaf explants on MS medium supplemented with 1.0 mgL-1 paclobutrazol and 1.0 mgL-1 naftalenacetic acid (RF=0.98). Optimal transformation conditions were obtained for both cultivars by co-cultivating leaf explants with Agrobacterium tumefaciens in liquid MS medium for 24 hours at 28°C in stationary cultures in the dark. Acetosyringone infuence on the transformation effciency was found to be dependent on the co-cultivation temperature but it did not increase the transformation effciencies. Molecular evidences by PCR, Southern blot and Dot blot demonstrated the effectiveness of the transformation procedure. The protocol described here is currently in use to produce transgenic sweet potatoes from different cultivars with high effciency.