Resistance to the peanut root-knot nematode ( Meloidogyne arenaria Race 1) has been identified in tobacco ( Nicotiana tabacum L.) breeding lines, commercial flue-cured tobacco cultivars and in related Nicotiana species. The inheritance of resistance to this nematode found in breeding lines 81-RL-2K and SA 1214, and the commercial flue-cured tobacco cv. Speight G-28 was investigated. The genetic relationship of this resistance in Speight G-28 to the resistance of the same cultivar to Races 1 and 3 of M. incognita was studied. Crosses were made between the root-knot nematode susceptible flue-cured tobacco cv. NC 2326 and the three resistance genotypes. Parental, F₁, F₂, and backcross generations (BC₁P₁,BC₁P₂) were grown for each cross in randomized complete block designs with five replications in the greenhouse. Detached leaves from individual plants of parental, F₁ and F₂ also were inoculated with isolate NC 138 of the MSNR strain of potato virus Y (PVY). This virus strain produces necrotic lesions on M. incognita-resistant plants because of the pleiotropic effects of the single gene conferring the root-knot resistance. The data obtained showed that resistance to M. arenaria (Race 1) in the three resistance sources, 81-RL-2K, SA 1214 and Speight G-28 is conditioned by a single dominant gene. The correlation of the reactions of the detached leaves to the virus and of the corresponding plants to the nematode was perfect (r~1.0). This indicates that resistance to Races 1 and 3 of M. incognita and M. arenaria (Race 1) in Speight G-28 is controlled by the same gene. Also, there was a perfect positive correlation between reactions to the virus and to the nematode in plant of both tobacco breeding lines 81-RL-2K and SA 1214 and their corresponding progenies. These results, combined with the absence of segregation in the F₂ populations of the crosses between resistant parents 81-RL-2K x SA 1214, 81-RL-2K x Speight G-28 and SA 1214 x Speight G-28, suggest allelism of resistance among these genotypes.