Successful vegetative propagation techniques for the threatened African pencil cedar (Juniperus procera Hoechst. ex Endl.)

摘要

Rooting efficiencies of cuttings derived from three age class stock plants of African pencil cedar (Juniperus procera Hoechst. ex Endl.), were studied using eight different concentrations of indolebutyric acid (IBA), viz. 0.00, 0.05, 0.10. 0.20. 0.40. 0.80, 1.60 and 3.20%. The number of cuttings used in anyone treatment ranged from 60 to 70. IBA applied at either 20 mug per cutting (for cuttings derived from 5-month-old stock plants) or at 40 mug per cutting (for cuttings derived from 10-and 15-month-old stock plants) resulted in significantly higher rooting responses compared to the control (P < 0.001). Whereas callusing in cuttings derived from the 5-month-old stock plants declined with increasing IBA level (r = -0.78, P < 0.05), rooting increased up to only 0.2% IBA. There were significant differences (P < 0.001) among the rooting responses of cuttings derived from 5- and 15-month-old stock plants, as well as among those derived from 10- and 15-month-old stock plants. The number of rooted cuttings and the corresponding root number declined rapidly when cuttings were treated with IBA beyond the 0.4% level. None of the cuttings derived from any of the age classes survived the lethal effects of IBA when this was applied at a concentration of 160 and 320 mug per cutting. By far the most significant effect of IBA was on the total root number. Mean root number increased by over three-fold in cuttings derived from all the three categories of stock plants when these were treated with 40 mug of IBA per cutting. The effectiveness of applied IBA in inducing rooting and in increasing the total root number increased with the age of stock plants from which cuttings were derived. Cuttings derived from 15-month-old stock plants needed higher IBA concentration, and the magnitude of the response (relative to the control, and in terms of rooting ability) was higher compared to those derived from 5-month-old stock plants. Interestingly, a significant number of cuttings derived from the more mature stock plants tended to produce roots without undergoing tissue dedifferentiation. Conversely, more than 95% of the control cuttings derived from 5-month-old seedlings produced calli, hence developing the majority of their roots after tissue differentiation had taken place. Growth of stecklings was proportional to the number of roots and (provided that growing conditions are optimal) planting size stecklings could be produced within about 10 months after transplanting rooted cuttings from the rooting medium to potted soils. With an overall rooting success of 60-80%, and with a reasonably good growth rate of stecklings, production of planting material from juvenile stock plants of J. procera through vegetative means, and through use of low-cost propagators, offers opportunities for a cheaper, practically sound and technically less demanding alternative means of propagation.