Effects of light on in vitro tuberization of the potato cultivar Desiree and its relatives

Effects of different combinations of short days and dark treatment and diff erent light intensities during the short days on in vitro tuberization of t hree potato cultivars were examined. Tuberization in Desiree, Cleopatra and Gracia was induced by short-day-treatment after 4 weeks culture under long days. To preserve natural endogenous hormonal balance of in vitro plantlet s growth regulators were not added to the medium. The shorter the duration of short-days period the higher light intensity necessary for earlier tuber initiation. There was also a synchronizing effect of the high light intens ity on tuber initiation but it depended on photoperiod-treatments and genot ypes. The higher the light intensity during induction period the less favou rable the effect of light applied after the induction period.