Inoculation with Nonpathogenic Fusarium solani Increases Severity of Pea Root Rot Caused by Aphanomyces euteiches

Aphanomyces euteiches is an important root-rotting pathogen of pea. When recovering isolates of A. euteiches from infested soils in Wisconsin using pea as a bait host, isolates of Fusarium solani often were recovered. Experiments were established to compare disease symptoms of pea seedlings inoculated with isolates of A. euteiches and F. solani alone or in combination. Inoculation of pea seedlings with either of two isolates of A. euteiches produced typical root rot symptoms. However, inoculation of pea seedlings with an isolate of F. solani resulted in no disease symptoms, indicating that the isolate was nonpathogenic to pea. Co-inoculation of pea seedlings with A. euteiches and the nonpathogenic isolate of F. solani resulted in significantly (P = 0.05) greater disease severity than inoculation with A. euteiches alone. Both A. euteiches and F. solani could be reisolated, individually or together, from pea seedlings following individual or co-inoculations, respectively. Although the mechanisms of interaction between these two species are unknown, the synergism documented in this study indicates that the interactions of pathogens with nonpathogens may affect development of disease symptoms.