Somatic chromosome number doubling of selected potato genotypes using callus culture or the colchicine treatment of shoot nodes in vitro

Experiments were carried out to double the somatic cell chromosome numbers of a monoploid and dihaploid of Solanum tuberosum and a genotype of S. circaeifolium subsp. quimense. Colchicine was used in vitro On shoot nodes from which the axillary meristems had been removed. Plants with doubled chromosome numbers were obtained from shoots grown from the tertiary, sub-axillary meristems of all three genotypes. The callus culture of stem and leaf explants was found to produce more shoots with doubled chromosome numbers than the colchicine treatment in the case of the dihaploid and quimense genotypes but no shoots were obtained from callus culture of the monoploid. Fifty-two % of the shoots from the dihaploid and 63% from the quimense clone were ploidy doubled in the case of the best callus culture system. Using a sub-lethal dose of colchicine, the dihaploid yielded 37% ploidy-doubled shoots whereas all the shoots produced from the monoploid were doubled and the quimense clone produced 27% doubled plants. Callus culture was highly dependent upon the type of growth medium and other, unknown, factors. The colchicine treatment, although yielding fewer products, was more reliable for achieving ploidy doubling in selected clones if the number of plants produced is not important.