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Ecology and Epidemiology

Effects of Temperature and Hydrogen Ion Concentration on Attachment of Macroconidia of Fusarium solani f. sp. phaseoli to Mung Bean Roots in Hydroponic Nutrient Solution. A. C. Schuerger, Senior plant pathologist, The Land, EPCOT Center, P.O. Box 10,000, Lake Buena Vista, FL 32830; D. J. Mitchell, Professor, Department of Plant Pathology, University of Florida, Gainesville 32611. Phytopathology 82:1311-1319. Accepted for publication 17 July 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-1311.

Hydroponically grown mung bean seedlings were inoculated with macroconidia of Fusarium solani f. sp. phaseoli to evaluate the effects of temperature (15, 20, 25, 30, and 35 C) and hydrogen ion concentration (pH 3, 4, 5, 6, and 7) on spore attachment to roots of Vigna radiata. Macroconidia of F. s. phaseoli attached to second-order roots with root hairs in greater numbers than to those without root hairs or to roots of other orders. Attachment of macroconidia to second-order roots was greatest at 2030 C and pH 4 but decreased by up to two orders of magnitude when the temperature of the nutrient solution was increased to 35 C or the pH elevated to 7. The binding reaction of macroconidia to roots was observed to be reversible when plants inoculated at 25 C and pH 5 were transferred to nutrient solutions maintained at 35 C or pH 7. Plant fresh weights of V. radiata decreased with increasing inoculum density when plants were inoculated and maintained at 20 or 25 C but not at 30 C. Differences in plant fresh weights of V. radiata between inoculated and uninoculated plants were greatest at 20 C, decreased at 25 C, and were not observed at 30 C. In a separate experiment, plant roots were exposed to inoculum for 24 h at 24 C and pH 4, 5, 6, or 7. The nutrient solutions of each treatment were then adjusted to and maintained at pH 6 for an additional 13 days. Disease was greatest when roots were inoculated at pH 4 as compared to pH 5 or 6. Plants inoculated at pH 7 were not different from uninoculated plants. Differences in disease among plants inoculated at different hydrogen ion concentrations are explicable when based on the effects of hydrogen ion concentration on the attachment of macroconidia to root surfaces. Differences in disease among plants inoculated at different temperatures between 20 and 30 C are not explicable when based on the effects of temperature on spore attachment to roots or on growth of the pathogen. We propose that differences in disease among plants inoculated between 20 and 30 C are due to the effects of temperature on host resistance.

Additional keywords: morphometrics, multiphase regression.