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Influence of Corynebacterium insidiosum on Water Relations of Alfalfa. Rastri Dey, Graduate research assistant, Department of Biology, Utah State University, Logan 84322; Neal K. Van Alfen, associate professor, Department of Biology, Utah State University, Logan 84322. Phytopathology 69:942-946. Accepted for publication 7 March 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-942.

The effect of Corynebacterium insidiosum on the water relations of alfalfa was studied in a 6-yr-old stand of Ranger alfalfa. Stomatal conductance, xylem pressure potential, and root, stem, and leaf liquid flow conductance were measured periodically. At all times, the xylem pressure potential was more negative in diseased than in healthy plants. Stomatal function was not impaired in either diseased or healthy plants. A 60-fold decrease in liquid flow conductance through petioles and leaflet veins of diseased plants probably was the cause of water stress. Flow of water through other parts of the vascular system of diseased plants was only slightly impaired. No evidence of cellular membrane damage was found in water regain or electrolyte leakage studies. The location of impaired water movement was not correlated with the location of the largest numbers of bacteria.