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Effect of Chlorine on Peronospora trifoliorum Sporangial Production and Germination. P. M. Fried, Graduate Research Assistant, Department of Plant Pathology, Kansas State University, Manhattan 66506; D. L. Stuteville, Research Plant Pathologist, Department of Plant Pathology, Kansas State University, Manhattan 66506. Phytopathology 65:929-930. DOI: 10.1094/Phyto-65-929.

Tap water (500 ml containing 0.5 µg/ml chlorine) placed below, but not in contact with, infected alfalfa plants in a 12.5-liter airtight chamber apparently released chlorine and other unidentified volatile chemicals that reduced Peronospora trifoliorum sporangial production 83% and sporangial germination 40%. The tap water was nontoxic after addition of sodium thiosulfate, or 24 hours of exposure to air in a shallow tray. When chlorine gas was added to deionized water at rates of 0, 0.25, 0.5, and 1 µg/ml, 44, 28, 20, and 0 sporangia × 10³/plant, respectively, were produced that germinated 86, 78, and 62%, respectively.