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The Effects of Plant Age and Leaf Position on the Susceptibility of Tobacco to Blue Mold Caused by Peronospora tabacina. M. Reuveni, Department of Plant Pathology, University of Kentucky, Lexington 40546; S. Tuzun(2), J. S. Cole(3), M. R. Siegel(4), and J. Kuć (5). (2)(3)(4)(5)Department of Plant Pathology, University of Kentucky, Lexington 40546, (3)Present address: Tobacco Research Board, P.O. Box 1909, Harare, Zimbabwe. Phytopathology 76:455-458. Accepted for publication 7 November 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-455.

A leaf disk assay was used to monitor susceptibility of greenhouse and field-grown tobacco plants to blue mold, caused by Peronospora tabacina. The susceptibility of leaf disks to the pathogen was influenced by the age of the plants and inoculum concentration. The area of lesions and sporangial production on leaf disks and attached leaves decreased with increasing age of plants. The position of the leaves on plants had less influence on susceptibility than did plant age. These data suggest the presence of a defense mechanism that appears to be dependent on the age of the plant but not the age of the leaves.

Additional keywords: Nicotiana tabacum.