FORCED FLUSHING OF BRANCH SEGMENTS AS A METHOD FOR OBTAINING REACTIVEEXPLANTS OF MATURE QUERCUS-ROBUR TREES FOR MICROPROPAGATION

The aim of this study was to micropropagate mature Quercus robur I,. t rees when material retaining physiologically juvenile characteristics (stump sprouts, epicormic shoots) is not available. Branch segments fr om 70-300 year-old trees were force-flushed and the flushed, partially rejuvenated or reinvigorated shoots were used as a source of explants for establishment of cultures. In vitro establishment and multiplicat ion was achieved with seven of the eight selected trees. The prolifera tion capacity of cultures of vertically placed explants declined after several subcultures, but efficient shoot multiplication was achieved by culturing decapitated shoots placed horizontally on GD medium suppl emented with 0.89 mu M of B-benzyladenine, Reculturing the same horizo ntal explant several times allowed both higher multiplication rates an d a shorter subculture cycle (2 weeks). An initial dark period of 5 da ys generally improved rooting capacity, which ranged, depending on clo ne, from 15 to 46%.