Abstract:

The capability of different cytokinins (BA, kinetin, zeatin, 2iP) to stimulate the induction and development of adventitious buds was determined after single and repeated induction steps with hypocotyl explants. BA was the most effective cytokinin as far as it concerned the number of induced adventitious buds. Zeatin, although less effective for this pattern, promoted the elongation of buds even after repeated induction cycles contrary to BA. This is important to get propagating bud clusters with the ability to form elongating shoots. A five-year-old propagating clone line of adventitious bud clusters was used to study the influence of zeatin and ammonium nitrate on the shoot elongation. Three induction variants (6.84,13.68, 20.52 μmol·L^-1 zeatin, each with 0.69 μmol·L^-1 kinetin for 4 weeks) were tested. The highest zeatin concentration induced the largest number of elongating buds. The influence of one subculture step with an enhanced ammonium nitrate concentration during the growth regulator free shoot development period (4 subcultures) was tested. A subculture on a medium free of growth regulators with a low ammonium nitrate concentration (2.5 mmol·L^-1 ) followed the cytokinin containing induction medium. The next subculture medium was supplemented with 2.5, 7.5, 12.5 and 17.5 mmol·L^-1 ammonium nitrate. An 8-week period (2 subcultures) followed with 2.5 mmol·L^-1 ammonium nitrate. The treatment with 7.5 mmol·L^-1 ammonium nitrate formed the highest number of elongating buds. This was identical for all zeatin concentrations used for induction. Increased ammonium nitrate concentrations during this treatment (12.5 mmol·L^-1 and 17.5 mmol·L^-1 ) decreased the number of elongating buds.

Key words: Norway Spruce (Picea abies), adventitious buds, cytokinin, ammonium nitrate