Light and genotype effects on in vitro tuberization of potato plantlets

In vitro tuberization responses of eleven clones of potato were evaluated u nder different photoperiods and light intensities. No growth regulators wer e added to the medium to avoid the potential modification of the response t o the environmental stimuli. Plantlets were grown on MS medium containing 3% sucrose for four weeks unde r long days (16 h). Tuberization was induced by short days (8 h). Five phot operiodic combinations and three light intensity treatments were applied. Light applied after the tuber induction phase delayed or inhibited tuber in itiation (at proper photoperiods both at 111 and 55 mu mol m(-2) s(-1) ligh t intensities at 24/15 degreesC day/night temperature). Darkness following the induction stage accelerated and synchronized tuber initiation after hig h light intensity. However, these effects of dark treatment depended on lig ht intensity applied in short days before dark treatment. There was an inte raction between the duration of darkness applied in photoperiodic treatment s and the light intensity applied in short days on tuber initiation. No rel ationship was observed between the maturity groups of clones tested and the ir tuber initiation responses. Tight interaction (P less than or equal to0. 01) of treatments and clones was proved by statistical analysis. Reliable t uberization and high rate of tuberization (1.20-1.52) can be reached using these hormon-free systems.