Ojcow birch (Betula oycoviensis) is a rare and not very well-known taxon naturally occurring in only a few sites for example in Poland, the Czech Republic, southern Sweden or Ukraine. The only site with a confirmed occurrence of Ojcow birch in our country is a natural monument near Volyně near Výsluní in the Ore Mountains, where several dozen individuals grow. For this reason, in the Czech Republic, the Ojcow birch is classified in the Red List as a critically endangered species, although the taxonomic status of this birch has not yet been resolved.
Ojcow birch in Czechia shows a low reproductive capacity, which further threatens its already very small population. An "external assistance" in the form of vegetative methods of reproduction could represent a hope for saving this unique birch and its gene pool. These methods consist in separating part of the original plant and growing a completely new individual out of this part. Researchers from the Faculty of Forestry and Wood Sciences have set themselves the goal to find out, whether such a method of reproduction is possible with the Ojcow birch. Another goal was to assess whether vegetatively created individuals are viable and, if so, which method of vegetative reproduction is the most suitable for this species. Three methods commonly used in practice were applied in the research.
One of these methods was the so-called micropropagation, which belongs in in vitro techniques. The multiplication of individuals occurs from meristematic cells of the mother plant, because these cells have preserved their dividing capability. The main advantage of in vitro methods is that the whole process takes place under controlled conditions and the addition of various substances (such as phytohormones) to the nutrient medium can relatively well regulate the growth of a new individual. Each species has specific requirements for the composition of the nutrient medium, and a specific protocol has not yet been developed for the Ojcow birch. Therefore, the protocol originally developed for white birch with the addition of various amounts of growth-promoting phytohormones was used in this study. Rooting of individuals in the nutrient medium proceeded differently depending on the amount of phytohormones added. However, after transferring the rooting individuals to the substrate, it was found that the new individuals continued to thrive comparably regardless of the original nutrient medium and amount of phytohormones.
In addition to the in vitro method, propagation was also tested by cuttings, in which a part of the mother plant was removed and was subsequently treated with growth stimulators and placed in the substrate. Previous similar experiments have shown that this method is difficult for some birch species, it was effective only partially and only for a few species. This study came to a similar conclusion in the Ojcow birch. The condition of the cuttings was evaluated at the end of the growing season and it turned out that no roots developed on any of the cuttings and no callus development on the basal part of the cuttings was observed, regardless they were treated with root stimulators or not. Cutting is difficult in the case of Ojcow birch, especially if the cuttings are taken from older trees.
The third method tested was grafting. The most common way of grafting birches is a union of an early sprouted rootstock and a winter graft of two-year-old wood, which typically inoculates within 2-3 weeks. The choice of a suitable rootstock is crucial, as some tree species (including birch trees) are incompatible and the graft does not grow with the rootstock. In the case of this study, white birch was used as a rootstock. This method achieved a partial success. Growth was observed in several of the tested Ojcow birch genotypes, and new shoots and assimilation organs were formed. It was also interesting to note that the specific grafting technique used did not affect the final individual's survival.
This study thus confirmed that vegetative methods of propagation could indeed be a way how to save the gene pool of endangered Ojcow birch. However, as the authors state, further research will be needed to improve in vitro procedures as well as the methodology of cutting and grafting. So we can only hope that the Ojcow birch will be saved in the Czech Republic.
Ing. Jan Vítámvás, Ph.D.
Jan Vítámvás works at the Department of Forest Ecology and his research focuses on the growth of plants (such as various birch species, aspen, mulberry, spruce or orchids) in in vitro cultures. His work includes also studies of the effects of stress (especially drought) on growth of the forest trees. At the faculty he teaches subjects dealing with dendrology and he also does excursions in the Arboretum near Kostelec nad Černými lesy which belongs to the Faculty of Forestry and Wood Sciences.
Author: Dagmar Zádrapová