From tumour to tuber; tumour cell characteristics and chromosome numbers of crown gall-derived tetraploid potato plants (Solanum tuberosum cv. 'Maris Bard').

Agrobacterium tumefaciens strains, known to induce tobacco crown galls that spontaneously develop shoots, were used to induce galls on cultured shoots of a tetraploid potato cultivar (Solanum tuberosum cv. 'Maris Bard'). Shoots also appeared spontaneously from the induced potato galls, although only after 2-4 months. The shoots were excised and cultured separately. Some of these frequently developed side-shoots from their axillary buds. They did not form roots and they produced opines, a strong indication that they were transformed and carried T-DNA. Grafts of the transformed plants were still able to develop tubers. Most of the tumour-derived shoots, however, formed roots, did not produce opines and were indistinguishable from the parental plants on the basis of morphology and chromosome numbers (48 chromosomes per cell). The results are discussed in relation to the origin of previously described variation among protoplast-derived potato plants and with respect to genetic engineering of tetraploid potato cultivars.