Effect of Arrival Order on Co-infecting Pathogens

Multiple pathogens commonly infect a single host individual, and it is possible for microbial pathogens to interact within a host. These interactions can shape disease outcomes. The order in which distinct pathogens infect the same host can influence the overall outcome of the pathogens’ interactions on the amount of disease each pathogen causes. To determine how the arrival order of two pathogens on a shared host affect disease severity, tall fescue (Lolium arundinaceum) leaves were inoculated with Colletotrichum cereale and Rhizoctonia solani either simultaneously or sequentially both with detached leaves and whole host plants. It was hypothesized that a prior-arriving pathogen could influence the infection success of the second-arriving pathogen. On detached leaves, proportion leaf area diseased was measured daily, and, in the growth chamber, lesion lengths were measured daily. In the detached leaf assay, when R. solani arrived after infection by C. cereale, disease symptoms were more severe than when R. solani was inoculated simultaneously with C. cereale. In the growth chamber experiment, R. solani lesions were bigger when it was inoculated simultaneously with R. solani. Additionally, a survival analysis, a measure of host response to infection rather than pathogen response to infection, indicated that leaves inoculated with R. solani before C. cereale died more and died faster than in any other condition. These growth chamber results suggest that the order in which pathogens infect a host can determine disease outcomes, and the contrasting results from the detached leaf assay suggest the importance of using whole hosts to fully capture factors that can influence pathogen dynamics. The effect of arrival order on disease has implications for potential shifts in the relative timing of pathogen epidemics due to changing climate conditions.Bachelor of Scienc