Abstract: This study deals with the relationship between root knot nematode and blackshank disease of tobacco plants in order to solve the problem of disease control,Field experiment was carried out in Xuchang County,Henan Province in 1986.A resistant variety Speight G 140 was planted in a field where both pathogens existed abundantly and were distributed evenly.Ridoanil and Temik were used to control black shank and root knot respectively or used together to control both diseases.The untreated plots were used as checks.The results indicate that there is significant positive correlation between the incidence of tobaacco black shank and the existence of root knot nematods.The correlation coefficient equals to 0.755^**,and the determination coeffident r²,which means,in this experiment,57% of black shank disease was caused by root knot nematode.A regression equation was derved as Y=disease index of black X=disease index of root This epuation expresses the quantitative cxperimental both pathogens under experimental conditions mentioned above.It nematode relationship.Tt is helpful for us to make control decision.

Key words: Black shanks, Root knot neimatode, Resistibility