Assessment of the potential sources of reproductive material of woody plants

Within programme selection focused on woody plant species for landscape and urban greenery the following steps are essential: qualitative assessment of the potential gene pool of the particular taxon, identification of the appropriate sources of reproductive material in the natural conditions and inclusion of the selected components of the gene pool in the selection and breeding programme of woody plants for targeted utilization in landscape vegetation units, as well as in urban areas.

In Slovakia the sources of reproductive material have not yet been identified for Sorbus domestica and Pyrus pyraster. Therefore, we devote a targeted assessment of phenotypic traits of individuals (growing on the original stands in the landscape), that can be used as a qualified source of the reproductive material (Fig. 2 and 3). The identification of the phenotypes suitable for wider plant production is a significant assumption for systematic planting and use of the mentioned woody plant species.

So far, attention has been paid to a reliable method of phenotypic classification of Sorbus domestica on original stands. Options and tools of their interpretation for selection of the sources of reproductive material were also analysed within a field study in the cadastre of the village of Zemberovce (Paganova & Macekova 2011). The scale of quantitative and qualitative parameters was elaborated and confirmed in 2011. For individual trees several parameters were determined which represent tree habit, tree growth and volume production (Fig. 4) (Tab. 1).

Architectural traits, such as patterns of branching or clonal spread and production of terminal versus axial inflorescences, may also vary plastically in certain taxa. These traits provide very important insight into the structural and ultrastructural levels at which phenotypic adjustment takes place in the plant body (Wu & Stettler 1998). Therefore, we also apply them within the selection of indigenous woody plant species and their phenotypes suitable for urban landscapes and greenery.

Crown traits, such as branch diameter, branch angle and branch frequency, are also important determinants for the quality of woody plants and timber products (Bowyer et al., 2002). These characteristics also affect the utilization of woody plants in urban areas with limited space for tree growth. According to the literature, variability of the growth habit and other growth characteristics of woody plants has been the object of extensive research and represent a good basis for selection and tree breeding. In contrast, the crown architecture and structural characteristics of trees are less at the centre of interest and only rarely applied in breeding programmes. It should be noted that structural tree characteristics, such as crown shape, crown diameter, crown density, branch diameter, branch angle and leaf area, influence efficiency and magnitude of radiation interception and competitive interactions with other trees (Emhart et al., 2007). These characteristics have significant influence on the use of individual trees on particular stands and its competitiveness and ecological influence. The crown architecture and the active area covered by an individual woody plant have potential influences on the surrounding environment.

Several tree quantitative parameters are measured: tree height (h), stem girth at height 1,3 m (Оїд), deployment of living crown (a) – vertical distance between the first living branch (that is a part of the living crown) and horizontal plane of the stem base (URL1). Crown diameter (b) – average horizontal distance between opposite points of the crown projection. This parameter is usually measured in at least four ways (Smelko, 2000) using a densiometer. The shape and area of the crown projection is determined with GPS (global positioning system). The branch angle is determined in four categories (<30°, 30 – 60°, 60 – 90°, 90°< ) according to the deflection of tree branches from the vertical axis (Fig. 4).

In addition to these quantitative parameters, the crown shape, crown density and several other qualitative characteristics (trunk shape, trunk development and cross sectional shape of the trunk) were evaluated within field study. The photo documentation of tree habit was made for each of the evaluated genotypes of Sorbus domestica and Pyrus pyraster. The records will be used for other graphic processing. Within analytical data processing the other quantitative parameters of the tree habit were calculated: crown length, crown area projection and crown volume.

The relationship between parameters of the tree crown and stem were calculated for both woody plant species based on mentioned quantitative data, as well as the relationship between crown architecture and structural characteristics ^ regression analysis; we attempted to define a range of structural parameters of the trees, which are characteristic for high-quality phenotypes (plus trees) of Sorbus domestica and Pyrus pyraster. The multivariate statistical methods (discriminant analysis etc.) were used for assessment.

Preliminary data obtained within the field study documented distinctive variability of the phenotypic parameters of Sorbus domestica (Paganova & Macekova, 2011). Five basic crown shapes were found: conical, ovate, globular, parabolic and semi-globular (Fig. 5) within the population of trees growing in one location. Good phenotypic characteristics were confirmed for 12 individuals among the whole number of 35 individuals of Sorbus domestica which were evaluated according to the phenotypic classifications within the field study. These trees can be later (after additional testing and assessment) included under selected sources of the reproductive material of Sorbus domestica.

Location of the evaluated individuals on their original stand was determined using GPS, which will facilitate identification of the trees in the future. GPS was used also for determination of the shape and area of the crown projection within the field data collection.

The aim of the tree assessment is establishment of a database of genotypes for both woody plant species (Sorbus domestica and Pyrus pyraster) from the territory of Slovakia and selection of phenotypes suitable for landscape design and urban greenery. Selection of suitable sources for a reproduction (Drobna & Paganova, 2010) and breeding programme of the mentioned species was identified from the database of genotypes based on the classifications of the phenotypic characteristics (Fig. 6).