Following research conducted using certain Oriental tobacco cultivars - Djebel in the seedbed, in vegetation pots and in the field in the period 1990-1999, it was found that among diseases affecting the seedling phase, the most frequent for the Oriental tobacco was black root rot, caused by the micromycete Chalara elegans (sin. Thielaviopsis basicola ). In the laboratory, in perfectly controlled conditions and using an original method of work, research was conducted using 10 Oriental tobacco cultivars - Djebel, on the role of nutritive elements in the germinative layer, the role of the chemical reaction of the soil (pH) and the role of soil moisture on the expression of tobacco resistance to black root rot. After obtaining the results we modified the scale of resistance to the disease caused by Chalara elegans , using marks from 1 to 9 (1 - lack of resistance; 2 - very sensitive; 3 - sensitive; 4 -moderately sensitive; 5 - sensitive to tolerant; 6 - tolerant; 7 - moderately resistant; 8 - resistant; 9 - very resistant). The study of the rhizosphere of the tobacco plantlets showed the important role of the bacterial microflora in limiting the attack of the micromycete Chalara elegans . The presence of bacteria from the genera Pseudomonas , Bacillus and Arthrobacte r reduced very significantly the number of spores of this micromycete. From the plurifactorial analysis of certain real causes which contribute to the expression of resistance of the Oriental tobacco cultivars to the attack of the pathogenic micromycetes in the seedbed, and especially of the species Chalara elegans (the role of the nutritive elements, the role of the chemical reaction of the soil and the role of the soil moisture) it was clearly proved that some cultivars resist to the attack of the diseases specific to the seedling phase even when the experimental factors are at their optimum for the pathogenic micromycetes. This is due to the genetic fund of the cultivar, which provides genetic resistance as it was noticed for the cultivars Djebel M 83, Djebel 252, Djebel 215, Djebel 144, Djebel 292 and Djebel 125, which will be used in the future as sources of genetic resistance in the breeding work, in order to obtain superior genotypes of Oriental tobacco.