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Resistance

Evaluation of Systemic Resistance to Blue Mold Induced in Tobacco Leaves by Prior Stem Inoculation with Peronospora hyoscyami f. sp. tabacina. Yigal Cohen, Department of Plant Pathology, University of Kentucky, Lexington 40546, Present address of senior author: Department of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel; Joseph Kuc, Department of Plant Pathology, University of Kentucky, Lexington 40546. Phytopathology 71:783-787. Accepted for publication 12 November 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-783.

Conidia of Peronospora hyoscyami f. sp. tabacina (which causes blue mold of tobacco) applied to the stem-root interface zone of potted burley tobacco plants induced systemic protection of the foliage against the blue mold disease caused by the same pathogen. Neither heat-killed or sonicated conidia of P. hyoscyami f. sp. tabacina nor untreated inocula of three other tobacco pathogens or three nonpathogens induced protection against blue mold. Protection was associated with the necrosis that developed in the external phloem and cambium of the stem subsequent to the initial inoculation with P. hyoscyami f. sp. tabacina. Approximately 2 wk was required for development of ~50% protection and 3 wk for ~95%. Resistance in the leaves of protected plants was not confined to the epidermis; conidia infiltrated into leaf panels failed to produce normal lesions.