Ts. Radoukova1*, Y. Dyulgerski2, L. Dospatliev3
1Department of Botany and Teaching methods in Biology, Faculty of Biology, Plovdiv University “Paisii Hilendarski”, 24 Tzar Assen, 4000 Plovdiv, Bulgaria 2Tobacco and Tobacco Products Institute Markovo, 4108 Plovdiv, Bulgaria
3Department of Pharmacology, Animal Physiology and Physiological Chemistry, Faculty of Veterinary Medicine, Trakia University, 6000 Stara Zagora, Bulgaria
Abstract. The aim of the study was to investigate heterosis events and to establish the influence of the direction of crossing on them. Manifestations of real and hypothetic heterosis are studied regarding the height of plants and number of leaves of ten hybrid combinations with the participation of indigenous varieties and lines of Burley tobacco. Each of them is introduced with its straight and opposite crossing. The results show that with regard to the plant height and number of leaves in all hybrid combinations, the values of the real heterosis are lower than those of the hypothetical. Тhe results show that the heterosis effect is more vivid regarding the number of leaves than the height of plants. Use of heterosis to increase the number of leaves in variety group Burley tobacco is promising.The direction of crossing exercises influence on the activities of heterosis effect regarding the examined indices, particularly in relation to the number of leaves. It is of great significance whether the participation of the parental varieties, during the crossing is as a maternal or paternal component. This requires forward and reverse crossing to be used in selection practice in view of the difference in the values of individual indicators which often result from them.