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A top-cross-mating design among 29 S 4 inbred lines and tester (cultivar 'Dukat') was carried out to study their breeding value in terms of general combining ability (GCA). The objectives of this study were to evaluate the acidity, soluble solids and dry matter contents in fruits of progeny F 1 in comparison with S 4 inbred lines as well as the cultivars (S 0 ); identify strawberry genotypes with high value of GCA for use in cultivar development; and determine mid-parent heterosis regarding S 4 inbred lines and cultivated strawberry. The 2-year observations showed statistically significant differences between tested genotypes in terms of the studied traits. The highest breeding value based on GCA was estimated for Chandler 123-5 for soluble solids and dry matter content, and Kent 7-6 for acidity. Estimated mid-parent heterosis had positive and negative values. The highest heterosis in terms of extract and dry matter content (26.71% and 17.50%, respectively) occurred in the offspring Chandler 123-5 9 'Dukat', but as regards acidity in hybrid Chandler 123-22 with cv. 'Dukat'. The study of genetic divergence by dendrograms may help to identify parents suitable for obtaining hybrids with higher heterosis effects.

Strawberries are a common and important fruit in human diet because of their high content of essential nutrients and beneficial phytochemicals, which have relevant biological activity in human health. In this study, six cultivars and 15 selected F1 hybrids between S4 inbred lines and tester (cv. ‘Dukat’) were evaluated in a field trial over a period of two consecutive years. The amounts of total anthocyanin, phenolics and vitamin C in fruits and antiradical activity were analysed. General combining ability (GCA) and mid‐parent heterosis were also determined for those characteristics. Among all the genotypes tested, the inbred lines of ‘Senga Sengana’ 17 showed the highest breeding value based on GCA for all studied traits. Estimated heterosis varied among genotypes tested. The highest heterosis in terms of vitamin C occurred in the offspring of clone 1387 18‐15 × ‘Dukat’, but with regard to phenols and antiradical activity in hybrid ‘Teresa’ 18‐15 with cv. ‘Dukat’. This study revealed that the differentiation in chemical composition of strawberry fruits between genotypes is clearly dependent on individual genotype combinations and demonstrated the presence of heterosis in phytochemical contents in some specific genotypic combinations.