Acquired Systemic Susceptibility to Infection by Tobacco Mosaic Virus in Nicotiana glutinosa L

In Nicotiana glutinosa L. formation of local lesions on lower leaves inoculated with tobacco mosaic virus increased the susceptibility of the upper leaves to infection in a subsequent inoculation. The increase in susceptibility was detected as an increase of up to 3"5-fold in the number of lesions produced on the upper leaf and a corresponding increase in the amount of virus RNA synthesized. The concentration of endogenous abscisic acid in the upper leaves was negatively correlated with susceptibility to infection. This acquired systemic susceptibility to infection in N. glutinosa is in direct contrast to the acquired systemic resistance to infection reported to occur in hypersensitive varieties of Nicotiana tabacum under similar conditions. Mechanisms which might be involved in the acquisition of systemic resistance or susceptibility are discussed.