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Physiology and Biochemistry

Soluble Carbohydrate Levels in Tobacco Systemically Protected Against Blue Mold by Stem Injection with Peronospora tabacina or Leaf Inoculation with Tobacco Mosaic Virus. S. Q. Pan, Department of Plant Pathology, University of Kentucky, Lexington, Kentucky 40546; X. S. Ye, and J. Kuc. Department of Plant Pathology, University of Kentucky, Lexington, Kentucky 40546. Phytopathology 83:906-909. Accepted for publication 25 March 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-906.

Susceptible tobacco plants were systemically protected against blue mold (Peronospora tabacina) by stem injection with sporangiospores of P. tabacina or inoculation of three to four lower leaves with tobacco mosaic virus (TMV). After stem injection (9–13 days), higher soluble carbohydrate levels were detected in stem tissues at the sites of injection and distant from the sites of injection in P. tabacina-injected plants as compared with control plants. Thirteen days after stem injection, higher soluble carbohydrate levels were detected in nonchallenged leaves of P. tabacina-injected plants than in those of control plants. The differences in carbohydrate levels between P. tabacina-induced and control plants increased as the protection against blue mold increased. After challenge with P. tabacina, the soluble carbohydrate levels in challenged leaves of both P. tabacina-induced and control plants decreased, but the levels in the induced plants remained higher than those in the control plants during the entire period after challenge. In contrast, there was no difference in soluble carbohydrate levels between TMV-induced and control plants in the inoculated lower leaves or uninoculated upper leaves before or after challenge. This suggests that soluble carbohydrates which accumulated in tobacco plants systemically protected by P. tabacina are unlikely to be important in either the induction of resistance or as resistance mechanisms.