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Water Relations in Safflower During Wilting Induced by Phytophthora Root Rot. J. M. Duniway, Department of Plant Pathology, University of California, Davis 95616; Phytopathology 65:886-891. Accepted for publication 20 March 1975. DOI: 10.1094/Phyto-65-886.

The possible causes of wilting in safflower plants infected with Phytophthora drechsleri were examined. Determinations of leaf water and solute potentials showed that wilting was due to water stress. The diffusive resistance of leaves to water vapor loss following inoculation was as high as, or higher than, the diffusive resistance of healthy leaves at the same water status and there was no alteration in the transpirational behavior of infected plants which could cause water stress. Measurements of recovery rates of plants from water stress were used to examine resistance to water uptake. Infection caused a marked increase in resistance to water uptake through root systems, but also caused a marked increase in resistance to water movement through the xylem of stems. The influence of infection on xylem resistance extended above the highest point of stem invasion by the pathogen.