The search for growth-reducing rootstocks has produced selections of 'Oblacinska' sour cherry (Prunus cerasus L.) and European ground cherry (Prunus fruticosa Pall.). The methodological approach to germplasm collection was a compromise between a search for specific characters and random sampling of the population. On the principle of 19 variables in 27 accessions, this research brought valuable and diverse plant material into rootstock breeding. The vigour of adult trees on their own roots ranged from extremely weak, such as in selections of European ground cherry (SV1, SV3, SV4) and 'Oblacinska' sour cherry (OV31), to vigorous genotypes such as sour cherry (OV33 and OV34) and P mahaleb. The natural habit of untrained trees varied from upright (e.g., SV7) to dropping (e.g., SW). Internode lengths ranged from 1.36 cm (in SV8) to 4.11 cm (in SV4). Based on a PCA scatter-plot, six diverse sub-groups showing significant intra- and inter-species variability were distinguished. These findings were supported by high values of heritability, from 78.83-92.20%, implying the potential for successful selection of dwarfing genotypes based on their phenotypic characters in succeeding breeding activities. Preliminary field studies suggested that the 'Oblacinska' genotypes OV31 and OV32, as well as the European ground cherry genotypes SV1, SV2, and SV4, may represent rootstocks with the lowest vigour.
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