Conservation of Betula oycoviensis, an endangered rare taxon, using vegetative propagation methods

Abstract

Ojcow birch (Betula oycoviensis Besser) is a rare Central European tree taxon, micro-populations of which are found in only several localities. With a view to maintaining the B. oycoviensis gene pool, this study tested the species’ potential for micropropagation, grafting, and propagation by cuttings. Plant material for vegetative propagation was collected from ten genotypes in the Czech Republic. In vitro culture was established from axillary buds surfaces sterilized with 0.1% HgCl2 and cultivated on woody plant (WP) medium supplemented with 1 mg l-1 6-benzylaminopurine (BAP). Two genotypes of the species were successfully multiplied by in vitro propagation using WP medium supplemented with 0-2 mg l-1 BAP. The BAP concentration of 1 mg l-1 proved to be optimal, yielding 2.5 new shoots per explant in genotype 516 and 3.5 shoots per explant in genotype 545. The shoots were rooted on half-strength Murashige and Skoog (MS) medium supplemented with various concentrations of α-naphthylacetic acid (NAA) and indole-3-butyric acid (IBA). The highest rooting percentages (72.5% and 77.5% for genotypes 516 and 545, respectively) were achieved on the medium with the combination of both auxins at concentrations of 0.3 mg l-1. The rooted plants were transferred ex vitro in substrate composed of sand, peat, and perlite (1:1:1) and acclimated in the greenhouse. After 4 weeks, more than 90% of plants survived. Grafting was carried out in spring using Betula pendula as rootstock. The efficiency of this technique ranged from 0% to 50% across genotypes, and 4 out of 10 genotypes were successfully propagated by grafting. The cuttings were treated with commercial root stimulators Stimulax I and Stimulator AS-1, planted in a mixture of peat and sand (1:1) in the greenhouse, and watered regularly. This technique resulted in 0% rooting, however, and no cutting survived until the end of the vegetation period. The results of this study show that protocols for in vitro propagation and grafting can be employed for effective mass propagation of B. oycoviensis, although these processes show genotype-dependent responses.