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Effects of Simulated Acidic Rain on Host-Parasite Interactions in Plant Diseases. D. S. Shriner, Department of Plant Pathology, North Carolina State University, Raleigh, NC 27607, Present address of author: Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box X, Oak Ridge, TN 37830; Phytopathology 68:213-218. Accepted for publication 23 June 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-213.

The effects of simulated rain acidified with sulfuric acid were studied on five host-parasite systems. Plants were exposed in greenhouse or field to simulated rain of pH 3.2 or pH 6.0 in amounts and intervals common to weather patterns of North Carolina. Simulated acidic rain resulted in: (i) an 86% inhibition of the number of telia produced by Cronartium fusiforme on willow oak (Quercus phellos); (ii) a 66% inhibition in the reproduction of root-knot nematode (Meloidogyne hapla) on field-grown kidney beans (Phaseolus vulgaris ‘Red Kidney’); (iii) a 29% decrease in the percentage of leaf area of field-grown kidney beans affected by Uromyces phaseoli; and (iv) either stimulated or inhibited development of halo blight on kidney bean (caused by Pseudomonas phaseolicola), depending upon the stage of the disease cycle in which the treatments were applied. The effect varied as follows: (i) simulated acidic rain applied to plants before inoculation increased disease severity by 42%; (ii) suspension of bacteria in acidic rain resulted in no infection; and (iii) acidic rain applied to plants after infection inhibited disease development by 22%. Results suggest that the acidity of rain is an environmental parameter which should be of concern to plant pathologists and agricultural and forest ecologists.

Additional keywords: pollution effects.