Purpose. To reveal breeding and genetic peculiarities of modern spring barley varieties for the “number of grains per main ear” trait and identify genetic sources of increased combining ability for involving in hybridization.Methods. Investigations were carried out at the V. M. Remeslo Myronivka Institute of Wheat of NAAS of Ukraine. Modern varieties of domestic (‘Virazh’, ‘Talisman Myronivskyi’, ‘Komandor’) and foreign (‘KWS Aliciana’, ‘KWS Bambina’, ‘Zhana’, ‘Explorer’) breeding were involved in crossing for a full (7´7) diallel scheme. Parents and F1 were studied in field conditions during 2014–2016.Results. The analysis of variance of combining ability has shown a significant advantage in varying of general combining ability (GCA) effects. The mean square of specific combining ability (SCA) was significantly less than the GCA, but reliable throughout the years. The reciprocal effect was reliable only in 2014. Stably high effects of GCA during all years of investigations were noted in the varieties ‘KWS Aliciana’ (1.18–1.62) and ‘Virazh’ (1.33–1.48). The variety ‘KWS Bambina’ was characterized by lower but reliable positive effects of GCA (0.43–0.99) as compared to mentioned above. Non-allelic gene interaction was not found, that allowed to calculate the basic parameters of genetic variation. During all years of investigations, dominant effects of genes (H1 and H2) prevailed over the additive (D) ones in phenotypic expression of grain number per main ear. Mean degree of dominance in the experiment (H1/D) has shown overdominance. The same pattern was also distinctive for the index of mean degree of dominance in the loci . The dominance was reliably directed. Dominant effects of genes increased grain content, and recessive ones reduced it. At least 3–4 genes (groups of genes) have been revealed which determined the effects of dominance. At the same time, recessive genes (F<0) or gene effects were prevailed quantitatively in the varieties investigated. A high coefficient of heritability in broad sense (H2 = 0.98) has shown a significant determination of phenotypic variability with genetic factors. The coefficient of heritability in narrow sense (h2 = 0.66–0.68) confirmed that despite the advantage of dominant effects over the additive ones, the contribution of the latter was also significant.Conclusions. The prevalence of dominant effects of genes in the phenotypic expression of the number of grains per main ear causes the need for sufficient sample size of hybrid material and points to the expediency of conducting a more “rigid” selection for phenotype in later generations. At the same time, the considerable contribution of additive effects and high values of heritability indices give reason to predict the efficiency of selections aimed at increasing the trait in created hybrid material. The varieties ‘Virazh’, ‘KWS Aliciana’, ‘KWS Bambina’ should be used as effective genetic sources to increase grain content in combination breeding.

Purpose. To reveal breeding and genetic peculiarities of modern spring barley varieties for the “number of grains per main ear” trait and identify genetic sources of increased combining ability for involving in hybridization. Methods. Investigations were carried out at the V. M. Remeslo Myronivka Institute of Wheat of NAAS of Ukraine. Modern varieties of domestic (‘Virazh’, ‘Talisman Myronivskyi’, ‘Komandor’) and foreign (‘KWS Aliciana’, ‘KWS Bambina’, ‘Zhana’, ‘Explorer’) breeding were involved in crossing for a full (7´7) diallel scheme. Parents and F1 were studied in field conditions during 2014–2016. Results. The analysis of variance of combining ability has shown a significant advantage in varying of general combining ability (GCA) effects. The mean square of specific combining ability (SCA) was significantly less than the GCA, but reliable throughout the years. The reciprocal effect was reliable only in 2014. Stably high effects of GCA during all years of investigations were noted in the varieties ‘KWS Aliciana’ (1.18–1.62) and ‘Virazh’ (1.33–1.48). The variety ‘KWS Bambina’ was characterized by lower but reliable positive effects of GCA (0.43–0.99) as compared to mentioned above. Non-allelic gene interaction was not found, that allowed to calculate the basic parameters of genetic variation. During all years of investigations, dominant effects of genes (H1 and H2) prevailed over the additive (D) ones in phenotypic expression of grain number per main ear. Mean degree of dominance in the experiment (H1/D) has shown overdominance. The same pattern was also distinctive for the index of mean degree of dominance in the loci . The dominance was reliably directed. Dominant effects of genes increased grain content, and recessive ones reduced it. At least 3–4 genes (groups of genes) have been revealed which determined the effects of dominance. At the same time, recessive genes (F<0) or gene effects were prevailed quantitatively in the varieties investigated. A high coefficient of heritability in broad sense (H2 = 0.98) has shown a significant determination of phenotypic variability with genetic factors. The coefficient of heritability in narrow sense (h2 = 0.66–0.68) confirmed that despite the advantage of dominant effects over the additive ones, the contribution of the latter was also significant. Conclusions. The prevalence of dominant effects of genes in the phenotypic expression of the number of grains per main ear causes the need for sufficient sample size of hybrid material and points to the expediency of conducting a more “rigid” selection for phenotype in later generations. At the same time, the considerable contribution of additive effects and high values of heritability indices give reason to predict the efficiency of selections aimed at increasing the trait in created hybrid material. The varieties ‘Virazh’, ‘KWS Aliciana’, ‘KWS Bambina’ should be used as effective genetic sources to increase grain content in combination breeding.