Effect of different photoperiods on in vitro growth of Mr.S. 2/5 plum rootstock

Trials were conducted to study the effect of different photoperiods on in vitro growth of Mr.S. 2/5 plum rootstock. Three photoperiods - 16 h (control), 12 h and 8 h - were applied, with a PAR of 39/~mol m -2 sec 1. Tips collected from in vitro established shoots were used; growth medium was MS with BA at 2.7/xM, GA 3 at 0.7/xM and IBA at 0.3/zM. Shoot proliferation after 45 days of growth was not statistically different between 12 h and 16 h of light, while the 8-h photoperiod gave a much lower rate of shoot formation. Shoot quality did not vary noticeably among the three treatments. Chlorophyll content and leaf thickness were not significantly modified even by a 50% reduction in light application. Stomata number and opening increased under 12 h of light. Rooting percentage was reduced by shortening the photoperiod to 8 h while root length was positively influenced with a 12-h photoperiod.