Meetings of the Royal Botanical Society of the Netherlands

Since July 1974 tobacco plants, which react hypersensitively to infection with tobacco mosaic virus (TMV), have occasionally been found to develop necrotic symptoms on non-inoculated upper leaves. A similar phenomenon was reported recently by Shimomura (Japan) who was unable to detect virus in the systemically reacting plant parts. In our laboratory systemic symptoms occurred on all hypersensitively reacting Nicotiana species tested by TMV inoculation: N. tabacum “Samsun NN”, N. tabacum “Xanthi nc” and N. glutinosa, although much less frequently in the last case. Varying percentages of “Samsun NN” plants developed systemic symptoms. A minimal dose of 0.2 pg TMV/ml was required for expression of the symptoms which increased in severity with higher virus doses. When either “Samsun NN” or N. glutinosa were grafted on “Samsun NN”, and the rootstocks were subsequently inoculated with TMV, systemic necrosis developed in the scions of both species. After re-inoculation with TMV of systemically infected leaves of “Samsun NN”, the usual systemic acquired resistance was expressed.