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 μmol m-2 sec-1. Tips collected from in vitro established shoots were used;ggrowth medium was MS with BA at 2.7 μM, GA3 at 0.7 μM and IBA at 0.3 μM. 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.
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