Effect of Rhizobium japonicum Nodulation on Severity of Phytophthora Root Rot of Soybean. Jean E. Beagle-Ristaino, Former Graduate Assistant, Department of Botany, University of Maryland, College Park 20742. Jane F. Rissler, Assistant Professor, Department of Botany, University of Maryland, College Park 20742. Plant Dis. 67:651-654. Accepted for publication 23 November 1982. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-651.

Phytophthora root rot of soybeans (Glycine max), caused by Phytophthora megasperma f. sp. glycinea (Pmg), is more severe on susceptible plants nodulated by Rhizobium japonicum than on plants not nodulated. Shoot growth and shoot and root dry weight means of inoculated Harosoy plants were lower and root rot scores were higher on nodulated plants than on those not nodulated. Disease severity of inoculated Harosoy 63 plants did not differ with or without nodulation. The Pmg-inoculated Harosoy plants had fewer nodules than did uninoculated Harosoy and Harosoy 63 plants, and Pmg colonized nodules of Harosoy but not Harosoy 63 soybeans.