| Sumario: | This study evaluated the reactions of seven commonC4 grasses of the tallgrass prairie of theUSA GreatPlains to the economically important wheat pathogensPyrenophora tritici‐repentisandGaeumannomyces graminisvar.tritici(Ggt) isolated from wheat. TheP. tritici‐repentisisolates (race 1) were pathogenic on all grasses tested, but symptom severity was markedly low. Three of the grass species inoculated withGgt were highly susceptible, while four species exhibited no symptoms. Because measures of connectedness can provide a proxy for population processes, connectedness was evaluated within and among the seven grass species in representative tallgrass prairie environments for all potential pathogen‐sharing patterns.Andropogon gerardiiwas ubiquitous, so all plant species were well connected to it.Andropogon scoparius(=Schizachyrium scoparium),Sorghastrum nutansandPanicum virgatumwere fairly common but specialized to particular environments.Bouteloua curtipendulawas uncommon but occurred in all environments, whileBuchloë dactyloidesandBouteloua graciliswere uncommon and only occurred in upland sites. Co‐occurrence of plant species was generally not reciprocal in that, for many species pairs, speciesArarely occurred without potential exposure to inoculum from speciesB, while speciesBcommonly occurred without speciesA. The three grass species susceptible toGgt may act as sources of inoculum for each other within tallgrass prairie, with the potential to influence fitness, and tallgrass prairie and commercial wheat ecosystems in theGreatPlains also have the potential to share both pathogens.
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