USE OF THE GROWTH RETARDANT TETCYCLACIS FOR POTATO-TUBER FORMATION IN-VITRO

The effects of the plant growth retardant tetcyclacis on in vitro tube r formation in potatoes was studied, using two different approaches: 1 . tuber formation in various lines that did not or hardly form tubers under control conditions, and 2. tuber formation by the variety Bintje , which readily forms tubers. The ABA-deficient (droopy) lines of S. p hureja hardly formed tubers without the addition of tetcyclacis. In th e presence of this growth retardant tuberization was nearly 100%, with in three weeks of in vitro culture, even in the absence of cytokinin. A series of somatic hybrids between S. tuberosum and S. brevidens, tha t did not form tubers in field and pot experiments, were tested. They all formed tubers in vitro in the presence of tetcyclacis. Stolonifero us shoots formed on single-node cuttings from in vitro grown Solanum t uberosum var Bintje plantlets were transferred to media containing a h igh level of sucrose. In the presence of tetcyclacis, tuber formation started after 4 days, reaching a maximum level of 80% at day 7. Tubers formed in the presence of tetcyclacis, accumulated starch and express ed several tuber-specific genes. These effects were fully antagonized by gibberellic acid. It is concluded that the growth retardant tetcycl acis is a potent tool in the study of tuber formation in potatoes.