According to Niina Stenvall's doctoral dissertation, as many as 200 stock plants per year can be produced with the root cutting method. For efficient rooting, root cuttings smaller than one centimetre in diameter were shown to be the most efficient.
The fast-growing hybrid aspen (Populus tremula L. x P. tremuloides Michx.) is needed in the paper industry for manufacturing of fine paper. Therefore, the number of forest plantations of hybrid aspen should be increased and seedling production should be developed and made more efficient to meet the needs of industry. However, there are considerable differences between the timber properties of individual hybrid aspens and not all of them comply with the quality requirements set by the paper industry.
Hybrid aspen can be regenerated both sexually (seeds) and asexually, through vegetative propagation (e.g. cuttings), but only the latter method can produce clones exactly like the parent tree and ones that fulfil the criteria of paper making. The aim of Nina Stenvall’s dissertation study was to develop an efficient and simple method of vegetative propagation for large-scale production of hybrid aspen seedlings for regeneration.
The results showed that the root cutting method is substantially more efficient than using stem cuttings. Depending on the clone, a two-year-old root-cutting stock plant can produce 81-207 plants, while the corresponding number by the stem cutting method is only 1-8 plants per year.
In practice, root cuttings taken from all parts of the hybrid aspen’s root system were shown to be capable of producing new shoots and roots, but roots smaller than one centimetre in diameter are the best, because rooting decreased when cuttings with a larger diameter were used. Increased soil temperature improved sprouting and rooting, as well as increased the sprouting rate. Cuttings sprouted faster when exposed to light, but on the other hand, rooting occurred better in dark.
Variation between the clones was considerable. Although the key criteria for selecting hybrid aspen clones are fibre properties and growth rate, the ability to regenerate efficiently is essential. The fact that the clones with the best sprouting results also rooted best facilitates clone selection for mass commercial propagation. For large-scale propagation it is important to select clones that produce a large number of cuttings per stock plant. As for the production costs, the regeneration capacity of the produced cuttings is even more important.
Publication: Stenvall, N. 2006. Multiplication of hybrid aspen (Populus tremula L. x P. tremuloides Michx.) from cuttings. Dissertationes Forestales 33.