Studies were conducted to assess the roles of the rhizosphere microflora and physical and chemical conditions in the seedbed on the resistance of some oriental tobacco cultivars to pathogens in particular Chalara elegans ( Thielaviopsis basicola ). The authors developed a laboratory device and made studies between 1994 and 1995 that established the influence of some factors on the resistance of certain oriental cultivars to black root rot. The factors were : a) Microflora in the rhizosphere; b) Nutrients in the seedbed; c) Soil reaction (pH); d) Soil moisture. The tobacco seedlings were produced in controlled conditions (in the laboratory) and were artificially inoculated with different doses of suspensions of Chalara elegans endoconidia, taken from infested plants and grown on nutritive medium. The resistance of each tested cultivar was monitored in relation with the controlled factors and the genetic basis of the cultivar. After the main symptoms of the disease appeared on the seedlings, the degree of infection of the tobacco plant roots was recorded. The growth rate of the small plants and duration of each phenological phase until the seedlings were ready to be transplanted were also recorded. Studies on the influence of the rhizosphere and edaphosphere on the resistance to black root rot were conducted. As a conclusion, the following cultivars proved to be resistant to black root rot : Djebel 252 (registered cultivar used in production), Djebel 267, Djebel 212 (a cultivar presently being registered), Djebel 125 and Djebel 145.