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Hydraulic Conductivity of Stem Internodes Related to Resistance of American Elms to Ceratocystis ulmi. J. B. Melching, Former Graduate Student, Department of Plant Pathology, Cornell University, Ithaca, New York 14853, Present address of senior author: 385-B Grant Road, Ft. Devens, Massachusetts 01433; W. A. Sinclair, Associate Professor, Department of Plant Pathology, Cornell University, Ithaca, New York 14853. Phytopathology 65:643-645. DOI: 10.1094/Phyto-65-643.

Segments of healthy internodes 3 or 4 years old from 32- to 36-year-old American elms previously selected as resistant to Ceratocystis ulmi, had significantly less capacity to conduct water than comparable segments from susceptible trees. Compared with noninoculated branches, water conductance 11 days after inoculation with C. ulmi was reduced 27% and 66% in resistant and susceptible trees, respectively. Ramets 2- to 4-year-old, of clones from resistant and susceptible trees showed no consistent differences in water conductance before or after inoculation with C. ulmi. Xylem pressure potentials of healthy clonal stock and clone-parent trees were not related to resistance.