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Effects of Cations on Germination of Urediniospores of Uromyces phaseoli. C. Jacyn Baker, Microbiology and Plant Pathology Laboratory, USDA, Beltsville, MD; J. Robert Tomerlin(2), Norton Mock(3), Lynn Davidson(4), and John Melhuish(5). (2)Germplasm Quality and Enhancement Laboratory, USDA, Beltsville, MD; (3)Department of Plant Science, University of Delaware, Newark; (4)Botany Department, University of Maryland, College Park; (5)Forestry Service, USDA, Berea, KY. Phytopathology 77:1556-1560. Accepted for publication 9 July 1987. 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, 1987. DOI: 10.1094/Phyto-77-1556.

Urediniospores of Uromyces phaseoli races 39 and 40 germinated better in unpurified tap water than in ultrapure laboratory water. Experiments with freeze-dried residue of tap water dissolved in ultrapure water suggested that the tap water contained a component that stimulated spore germination. When ions were removed from the tap water with ion-exchange resins, only cation-exchange resins decreased spore germination. Analysis of the tap water demonstrated that the major inorganic cations present were Ca2+, K+, Mg2+, and Na+. Spores of both races were incubated for 34 hr with solutions containing varying amounts of these cations. Germination was measured with a microscope to view 100 spores for each of five replicates. Calcium, at concentrations between 0.1 and 3 mM, was found to have a stimulatory effect proportional to the amount of cation present. Concentrations of calcium greater than 3 mM had little or no additional effect on germination. Spore germination in the presence of Ca2+ was comparable to that of tap water. Magnesium had a lesser effect on spores with statistically significant increases in germination requiring higher cation concentrations of about 1 mM. Maximum germination in the presence of Mg2+ was about 30% that of calcium. The monovalent cations tested at concentrations of 0.1 to 8 mM had little stimulatory effect on germination.