Adventitious shoot regeneration fromFagus sylvatica leaf explantsin vitro

Adventitious shoots were induced on transversally divided expanding leaves fromFagus sylvatica shoot cultures of juvenile origin. Adventitious shoot buds formed mainly on callus that developed on the petiole stump or on the cut across the midrib of distal leaf halves. However, sometimes they arose directly from leaf tissue. An anatomical study confirmed both the direct and indirect origin of the adventitious buds. The best results were obtained by culturing proximal leaf sections on woody plant medium supplemented with 2.9 μM indole-3 acetic acid in combination with 8.9 μM benzyladenine or 2.3 μM thidiazuron (TDZ). Proximal explants were more responsive than distal explants in terms of both callus formation and bud regeneration, regardless of the induction medium or clone tested. Bud formation capacity was influenced by the genotype of the stock shoot culture and was enhanced by an initial 10 d darkness, but was inhibited by longer periods of darkness. Caulogenic competence was significantly affected by the duration of exposure to TDZ; in particular, adventitious shoot length was depressed by increasing the exposure period. Three weeks culture with TDZ was the most efficient treatment for shoot production and elongation. Further shoot development was promoted by subculturing the explants to the same medium used for the maintenance of the stock shoot cultures. Shoots so obtained were multiplied and rooted producing plantlets of adventitious origin.