Oxidation-Reduction Potential of Chlorine Solutions and Their Toxicity to Erwinia carotovora subsp, carotovora and Geotrichum candidum . P. G. ROBBS, Universidade Federal Rural do Rio Janeiro, Departemente de Technologia de Alimentos, Rio de Janeiro, Brazil. J. A. BARTZ, Plant Pathology Department, University of Florida, Gainesville; and J. K. BRECHT and S. A. SARGENT, Horticultural Sciences Department, University of Florida, Gainesville. Plant Dis. 79:158-162. Accepted for publication 7 November 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0158.

The toxicity of chlorine solutions to cells of Erwinia carotovora subsp, carotovora and conidia of Geotrichum candidum suspended in water at pH 6.0, 7.0, or 8.0 was correlated with the free chlorine concentration and oxidation-reduction potential of the solutions. The oxidation-reduction potential was directly correlated with the Log10 of the chlorine concentration at each pH. Cells of E. c. carotovora were 50 times more sensitive to chlorine than were conidia of G. candidum, with populations of 1 x 107 cfu/ml and 1 x 107 conidia per milliliter, respectively. Populations of E. c. carotovora were reduced below detectable levels (<102 cfu/ml) by approxi-mately 0.5, 0.5, or 0.75 mg of free chlorine per liter at pH 6.0, 7.0, or 8.0, respectively. In contrast, with conidia of G. candidum, 25, 25, and greater than 30 mg/L, respectively, were required to produce a similar level of efficacy. With both organisms, population reductions were associated with higher initial oxidation-reduction potentials at pH 6.0 than al pH 8.0.

Keyword(s): hypochlorite ion, hypochlorous acid, Postharvest diseases