Research Notes Common Bean Root Exudates Contain Elevated Levels of Daidzein and Coumestrol in Response to Rhizobium Inoculation. Felix D. Dakora. Department of Agronomy & Range Science, University of California, Davis 95616 U.S.A. Cecillia M. Joseph, and Donald A. Phillips. Department of Agronomy & Range Science, University of California, Davis 95616 U.S.A. MPMI 6:665-668. Accepted 11 June 1993. Copyright 1993 The American Phytopathological Society.

Root exudate of common bean (Phaseolus vulgaris) inoculated with symbiotic Rhizobium leguminosarum bv. phaseoli bacteria contained more of the phytoalexin coumestrol and its isoflavonoid precursor daidzein than did exudates of uninoculated plants. Both compounds induced transcription of a nodC::lacZ fusion in R. l. bv. phaseoli. Because coumestrol is elicited in bean by pathogens, these results indicate that parallel biochemical changes occur when this legume responds to symbiotic and pathogenic microbes.