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Physiological Changes in Pathogen-Free Tissue of Ulmus americana Induced by Ceratocystis ulmi. W. Ronald Landis, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823, Present address of senior author: Niagara Chemical Division, FMC Corporation, Middleport, New York 14105; John H. Hart, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823. Phytopathology 62:909-913. Accepted for publication 21 February 1972. DOI: 10.1094/Phyto-62-909.

The response of pathogen-free tissue of American elm, Ulmus americana, infected with the Dutch elm disease pathogen, Ceratocystis ulmi, was studied. Oxygen uptake of pathogen-free leaf discs began to increase 5 to 11 days after inoculation of trees, and reached a maximum between 11 and 22 days, when oxygen uptake was as much as 80% higher than in controls. Thereafter, oxygen uptake decreased until it was less than controls 20 to 26 days after inoculation. Increased oxygen uptake was not caused by water stress, since potted elms under water stress had lower oxygen uptake than did normally watered controls. Conductivity of aqueous leachates from leaves was greater for inoculated than for control plants; this increased loss of electrolytes was correlated with increased oxygen uptake until maximum oxygen uptake was reached. When oxygen uptake began to decrease, conductivity began a rapid increase, reaching over 300% of controls when oxygen uptake was at its minimum of 30 to 50% of controls. Reduction of triphenyltetrazolium chloride demonstrated that twigs from which the leaves were harvested for respiration and conductivity experiments contained living parenchyma. Increased respiration and changes in permeability in pathogen-free tissues from infected plants support the hypothesis of a translocatible toxin.