In this study, the estimation of heterosis and the combining abilities for quantitative resistance against Blue Mould (Peronospora tabacina Adam) of eight oriental tobacco cultivars are presented. For this purpose, a half-diallel cross and its parents were arranged in four replications of a randomized block design. Symptoms of natural infestation of disease were observed and evaluated acording to CORESTA-methodology, during three years.
From the data presented on the combining ability and heterosis for quantitative Blue mould (Peronospora tabacina Adam) resistance in oriental tobacco, the following statements might be drawn:
- Significant general combining ability (GCA) was found, whereas the specific combining ability (SCA) was significant only in some individual crosses, and a great part of the general combining ability could be explained by variety effects. Significant variety heterosis was obtained too, and significant average heterosis was also obtained, but its effect was small.
- Among those selected for this study, "Bel 61-9’’ and ‘’Hicks- Rezistent" were the best for further crosses for tobacco resistance against P. tabacina Adam. | 
