Rooting of hybrid clones of Populus tremula L. ½ P. tremuloides Michx. by stem cuttings deri×ed from micropropagated plants.Propagation costs could be cut by replacing part of the micropropagation process with steps involving more traditional techniques. This study explored possibilities for improving existing vegetative propagation techniques for aspen using stem cuttings obtained from micropropagated plants. Vegetative propagation through stem cuttings was studied in 10 micropropagated hybrid aspen clones (Populus tremula L. ½P. tremuloides Michx). Cuttings containing one axillary bud were harvested from the same donor plants twice during the growing season: the rst harvest in May and the second harvest in July. Rooting percentage was correlated positively with root length, number of roots and height of cutting plant but negatively with length of rooting. The average rooting percentage was 53% in the rst harvest and 27% in second harvest. Indole-3-butyric acid treatments (1.2 mM) signi cantly improved rooting in the second harvest, but not in the rst harvest, suggesting different endogenous auxin levels in the cuttings. A signi cant variation for most traits related to rooting ability was found among the clones, indicating that clonal effects play an important role in the propagation of aspen. Thus, clones with a good response in shoot growth and rooting could be exploited in large-scale propagation using stem cuttings.

The ectomycorrhizal fungi, Pisolithus tinctorius (Pers.) Coker & Couch and three Paxillus involutus (Batsch) Fr. strains, were used to enhance in vivo rooting in fascicular shoots of 49 Scots pine (Pinus sylvestris L.) genotypes representing seed families from southern and northern Finland. Inoculation with specific fungi either increased the rooting percentage or accelerated root formation expressed as an increased number of adventitious roots per cutting. Only one of the six seed families gave no positive response. The relationship between the in vitro production of free and conjugated forms of indole-3-acetic acid (IAA) by the fungi and rooting was also investigated. Pisolithus tinctorius was the only significant producer of IAA in the absence of exogenous tryptophan. All the Paxillus involutus strains also synthesized both free and conjugated IAA but did that actively only from exogenous tryptophan. In vitro production of IAA did not correlate with root induction in vivo, but the rooting responses depended on the fungus strains and the Scots pine seed families and (or) genotypes within families. This indicates that in vitro IAA production capacity cannot be the only criterion when selecting ectomycorrhizal fungi for rooting in vivo and that specific genotype-genotype interactions play a key role in root initiation.

No abstract

No abstract

Rooting of hybrid clones of Populus tremula L. ½ P. tremuloides Michx. by stem cuttings deri × ed from micropropagate d plants.Propagation costs could be cut by replacing part of the micropropagation process with steps involving more traditional techniques. This study explored possibilities for improving existing vegetative propagation techniques for aspen using stem cuttings obtained from micropropagated plants. Vegetative propagation through stem cuttings was studied in 10 micropropagated hybrid aspen clones (Populus tremula L. ½P. tremuloides Michx). Cuttings containing one axillary bud were harvested from the same donor plants twice during the growing season: the rst harvest in May and the second harvest in July. Rooting percentage was correlated positively with root length, number of roots and height of cutting plant but negatively with length of rooting. The average rooting percentage was 53% in the rst harvest and 27% in second harvest. Indole-3-butyric acid treatments (1.2 mM) signi cantly improved rooting in the second harvest, but not in the rst harvest, suggesting different endogenous auxin levels in the cuttings. A signi cant variation for most traits related to rooting ability was found among the clones, indicating that clonal effects play an important role in the propagation of aspen. Thus, clones with a good response in shoot growth and rooting could be exploited in large-scale propagation using stem cuttings.