VIEW ARTICLE

Physiology and Biochemistry

Effect of Phytophthora Root Rot on Na⁺ Uptake and Accumulation by Safflower. T. R. Weicht, Graduate student, Department of Plant Pathology, University of California, Davis 95616, Present address: Department of Plant Pathology, North Carolina State University, Raleigh 27695; J. D. MacDonald, Professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 82:520-526. Accepted for publication 17 December 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-520.

Experiments with healthy and Phytophthora cryptogea infected safflower plants grown in nutrient solution containing 0, 50, or 100 meq L^–1 of NaCl/CaCl₂ (in a 10:1 equivalent ratio) showed that the concentration of Na⁺ in leaf tissue after 35 days was positively correlated (P < 0.001) with root rot severity. Relative to healthy controls, foliar Na⁺ concentration was significantly higher in plants with ≥40% root infection. Pathogen-induced changes in Na⁺ transport were investigated in various accumulation and efflux experiments. After pulse exposures of 1–60 min, the rate of ²²Na⁺ accumulation and the final concentration in root and shoot tissues of diseased plants were significantly (P < 0.01) higher than in healthy plants. When roots were incubated in ²²Na⁺ solutions and then immersed in unlabeled, iso-osmotic solution, healthy roots lost 7–10% of accumulated ²²Na⁺ after 10 h, whereas diseased roots had a significantly higher rate of efflux and lost up to 55%. The efflux experiments suggested that increased Na⁺ uptake and accumulation by diseased plants was the result of Phytophthora-induced changes in root permeability to Na⁺.