ACCUMULATION OF SCOPOLETIN IS ASSOCIATED WITH THE HIGH DISEASE RESISTANCE OF THE HYBRID NICOTIANA-GLUTINOSA X NICOTIANA-DEBNEYI

The high disease resistance of the amphidiploid hybrid of Nicotiana gl utinosa x Nicotiana debneyi is associated with high constitutive level s of two phenolic compounds as analysed by high-performance liquid chr omatography. The structures of these two compounds were elucidated by means of gas chromatography-tandem mass spectrometry, fluorescence- an d light-spectrophotometry to be those of scopolin and scopoletin. They reached levels of 4 nmol.(g FW)-1 and 35 nmol.(g FW)-1, respectively, in leaf tissues of the hybrid, about 10-50 times the amount found in the parental species. Scopoletin showed a direct antimicrobial activit y against Cercospora nicotianae, Phytophthora parasitica var. nicotian ae, Pseudomonas syringae pvs. tabaci and syringae and tobacco mosaic v irus when added to synthetic growth media, mixed with the inoculum or sprayed onto tobacco plants prior to inoculation. We postulate that th e high amount of toxic phenolics in the leaves of the hybrid N. glutin osa x N. debneyi contributes to its high disease resistance.