Transformation of potato using mannopine and cucumopine strains of Agrobacterium rhizogenes

Mannopine and cucumopine strains of Agrobacterium rhizogenes were used for genetic transformation in two cultivars of potato (Solanum tuberosum L.). An overnight pretreatment of stem fragments with NAA prior to bacterial infection was necessary to induce root formation, otherwise very few roots were produced. Whatever the potato cultivar used, rhizogenesis induced by NAA pretreament depended on the bacterial strain. In fact, when explants from both potato cultivars were pretreated with 26.5 μM NAA, on average 84.4% and 71.9% produced roots after inoculation with the strains 2659 and 2659 GUS respectively. On the contrary, few rhizogenic responses (2.0–17.0%) or no response at all (0.0%) were obtained with the strains 15834 and 8196 GUS whatever NAA concentration used. Tests for confirming stable transformation of plant explants by examining both β-glucuronidase activity and the presence of opines showed that 85% of the selected roots were cotransformed. Most of the transformed roots were highly branched and grew rapidly, compared to non-transformed roots with no branching and poor growth. Transgenic plants were readily regenerated with a frequency reaching 80% of total explants tested for both potato cultivars.