DIRECT REGENERATION OF TRANSFORMED PLANTS FROM STEM FRAGMENTS OF POTATO INOCULATED WITH AGROBACTERIUM-RHIZOGENES

Mannopine and cucumopine strains of Agrobacterium rhizogenes were used for genetic transformation in two cultivars of potato (Solanum tuberi sum L.). An overnight pretreatment of internodes with alpha-naphthalen eacetic acid prior to bacterial infection was found to strongly inhibi t shoot formation. On the contrary, infection with bacterial strains e nhanced the frequency of shoot formation, compared with the controls, except for the strain 15834 which completely inhibited shoot formation in both potato cultivars. Shoots developed directly from the upper pa rt of both inoculated and control explants, at a frequency ranging fro m 1 to 5 shoots per fragment. Among 93 shoots regenerated, 9 were foun d to be opine positive, and exhibited an altered phenotype with shorte ned internodes. Histological study revealed that the transformed shoot s developed directly from cells of the internode sections, and not fro m induced roots. When grown in an insect-proof tunnel, the transformed plants had both altered and normal phenotypes and were able to produc e tubers.