Combinational ability of varieties and self-pollinated lines of industrial hemp for seed and oil use in the topcross system

Purpose. To determine the peculiarities of total combining ability (TCA) and variances specific combining ability (SCA) effects of maternal components and test varieties of intervarietal and linear-varietal hybrids of monoecious hemp on the basis of seed productivity and oil content, to determine the predominance of additive or non-additive gene effects and to identify components with the highest breeding value, to give a forecast of the effectiveness of selection in hybrid populations. Methods. Combining ability was determined in the system of complete topcrosses. The varieties ‘YUSO 31’, ‘Demetra’, ‘Artemida’, ‘Aphrodita’, ‘Harmoniia’, ‘Hlesiia’, ‘Hlukhivski 33’, ‘Hlukhivski 51’ and their self-pollinated lines of the fourth generation were used as maternal forms, which were crossed with three test varieties ‘Hliana’, ‘Aphina’ and ‘Mykolaichyk’ (48 hybrid variants in total). The results of measurements were interpreted by arithmetic mean, F-test (R. A. Fisher), least significant difference and ranked. Results. The study of hemp varieties and their self-pollinated lines by the parameters of combining ability as maternal components of crosses showed significant differentiation by the effects of TCA (from −22.60 to 21.40 by inflorescence length, from −10.35 to 15.15 by seed weight, from −3.91 to 3.23 by thousand seed weight, from −2.40 to 3.76 by oil content) and SCA variances (6.72–233.23; 3.25–78.29; 0.01–0.10 and 0.01–2.10, respectively). The highest SCA was observed in the maternal forms of ‘Aphrodita’, I4 ‘Aphrodita’, I4 ‘Demetra’ and I4 ’Hlukhivski 51’ and the tester variety ‘Aphina’. A comparison of the effects of TCA and SCA variances revealed that the ‘Aphrodita’ variety and its self-pollinated line I4 were the best crossing components. Conclusions. In the analysed crosses, the additive effects of genes prevail in terms of thousand-seed weight and oil content, indicating the feasibility of selecting for phenotype. In contrast, non-additive effects prevail in terms of inflorescence length and seed weight, indicating the need for genotype selection. To increase seed productivity and oil content through combination breeding, it is advisable to use linear-varietal crosses where the maternal components have either high TCA and high SCA or medium TCA and high SCA.