LIGHT QUALITY OF THE IN-VITRO STAGE AFFECTS THE SUBSEQUENT ROOTING AND FIELD PERFORMANCE OF BETULA-PENDULA (ROTH)

The influence of irradiance and light quality on in vitro cultures was studied at the rooting stage, and subsequently as it affected the fie ld performance of birch (Betula pendula Roth.). Forty-five mumol m-2 s -1 during the rooting stage reduced the rooting time compared with 30 mumol m-2 s-1. The light quality treatments of the cultures, from whic h the microcuttings were harvested, had a larger effect on the rooting than the treatments during the rooting stage. The fastest rooting was observed in microcuttings pre-treated with blue light (6 days), and t he slowest rooting after treatments with red light (12 days), which al so, respectively, gave the highest (5.1) and lowest (3.5) mean number of roots per microcutting. The largest growth rate in the field was ob served in plantlets harvested from cultures subjected to blue and cool white light.