© 1995 Heron Publishing—Victoria, Canada
Influence of environment, fertilizer and genotype on shoot morphology and subsequent rooting of birch cuttings
Margareta Welander
Swedish University of Agricultural Sciences, Department of Horticulture, Box 55, S-230 53 Alnarp, Sweden / Received June 30, 1993
Summary
Differences in rooting ability of birch (Betula pubescens J.F. Ehrh.) cuttings were observed as a result of differences in genotype and physiology of the stock plants. The uniformity
in response among cuttings from micropropagated plants compared with cuttings from seed plants confirmed the advantage of
using micropropagated plants to study environmental effects. Shoot morphology of the seed stock plants was influenced by both
photoperiod and thermoperiod. A day/night temperature of 15/25 °C reduced stem elongation compared with a day/night temperature
of 25/15 °C regardless of photoperiod, and a continuous light regime resulted in more shoots per plant in both temperature
regimes than a 16-h photoperiod. A reduction in the supply of macronutrients did not influence shoot morphology, but increased
rooting substantially and seemed to override the effects of environmental factors. In cuttings of seed plants, the highest
rooting percentage and number of roots were obtained in a 16-h photoperiod with a day/night temperature of 15/25 °C. In micropropagated
stock plants, there was a positive correlation between shoot length and number of leaves per shoot and topographical distribution
of light within the plants, but there was no correlation between these parameters and rooting ability of the cuttings. A rooting
temperature of 16 °C delayed the rate of root production compared with the rate at higher temperatures, but the final rooting
percentage was the same over the range from 16 to 28 °C. Root branching increased with temperature. At all temperatures, there
was a large increase in sucrose content at the base of the cuttings during rooting, whereas the concentration of nontranslocated
sugars remained constant. The carbohydrate content at the base of cuttings from micropropagated stock plants was three times
higher than at the base of cuttings from seed stock plants, but the higher carbohydrate content was not correlated with a
higher rooting potential.
Keywords:
Betula pubescens, hydroponic system, micropropagation, photoperiod, temperature, thermoperiod.
