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Interactions of Simulated Acidic Rain with Root-Knot or Cyst Nematodes on Soybean. S. R. Shafer, Research plant pathologist (USDA-ARS) and associate professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616; S. R. Koenning, and K. R. Barker. Research analyst, and Professor, respectively, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 82:962-970. Accepted for publication 18 May 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992. DOI: 10.1094/Phyto-82-962.

The influence of simulated acidic rain on interactions of root-knot (Meloidogyne hapla, M. incognita) or cyst (Heterodera glycines) nematodes with soybean plants (Glycine max) was investigated in greenhouse experiments. Seedlings inoculated with rhizobia were transplanted into pots of nematode egg-infested soil (one nematode species per pot) or noninfested soil. Three days later, plants and soil were exposed to simulated rain (2 cm in 1 h) adjusted to pH 5.3, 4.3, 3.3, or 2.3. After three rains per week for 8 wk, major effects on plants and nematodes (e.g., shoot dry weight and production of cyst nematode eggs suppressed by approximately 80 and 90%, respectively) occurred only after rains at pH 2.3 (relative to those exposed to rains at pH 5.3). Characteristics of polynomial dose-response relationships indicated that the effects of simulated acidic rain on plants and nematodes were nematode species-dependent; dose-response relationships for many dependent variables (plant biomass, nodulation, disease symptoms, nematode reproduction measurements) versus rain pH differed between cyst nematodes and root-knot nematodes, but most dose-response characteristics for the two Meloidogyne spp. were similar. Acid deposition can influence nematode-plant interactions, but the acidity of simulated rain required to cause major changes exceeded that known in the United States.

Additional keywords: acid deposition, acid precipitation, Bradyrhizobium japonicum, nodulation, pollutant-parasite interaction.