P-396 - What is the host range of Cadophora gregata, causal agent of brown stem rot soybean?

Brown stem rot caused by Cadophora gregata is an important disease of soybean, mung bean and adzuki bean. This soil borne fungal pathogen damages stems and leaves and can cause significant yield losses. The host range of isolates of C. gregata from soybean is not well understood. A study was conducted with 21 legume species representing common crop and native plant species in the Midwestern U.S. Plants were inoculated in replicated studies with two types of C. gregata (A and B) via stem and root inoculation methods. Inoculated plants were maintained in a greenhouse and assessed for pathogen colonization and/or internal stem browning at 7 weeks post-inoculation. Colonization of plant stems by C. gregata was determined with a species-specific qPCR assay. Symptomatic hosts were those that developed typical internal stem symptoms of BSR in each experiment. Asymptomatic hosts did not develop typical internal brown symptoms but had levels of colonization by C. gregata similar to the levels measured in soybean, which was used as the positive control, in repeated experiments. The preliminary results suggest that some species of Phaseolus and Vigna are symptomatic hosts, and some species of Amorpha, Desmodium, Lespedeza, Phaseolus, Pisum, and Vigna are asymptomatic hosts. Thus, C. gregata appears to have a wider host range than previously reported, which may influence management and ecology of the pathogen.