Resistance of Tobacco to Thielaviopsis basicola under Tissue Culture Conditions and Increased Susceptibility after Transformation with Agrobacterium tumefaciens T‐DNA

Tobacco callus cultures from a Thielaviopsis basicola (Berk. et Br.) Ferraris resistant cultivar were less severely colonized than callus cultures from susceptible cultivars by the pathogen at all concentrations of kinetin and α‐indoleacetic acid tested. However, at concentrations where these substances influenced the morphology of the callus cultures they also influenced the degree of colonization by the fungus. Incorporation of T‐DNA of Agrobacterium tumefaciens induced susceptibility in tissue culture of the resistant cultivar but did not significantly modify the reaction of the susceptible cultivar tested.