P-171 - How do co-occurring pathogens influence disease dynamics of the focal pathogen?

Mixed infections by multiple pathogenic strains, species, genera or taxa are common in nature and the agricultural settings. As compared to infection with a single pathogen (monoinfection), mixed infections can alter disease dynamics mediated through modification of the host response by either pathogen, interactions among the co-existing pathogens, or through emergent responses to these multi-trophic interactions. We studied how co-occurring pathogens/pests, including pathogenic Pseudomonas syringae, parasitic root-knot nematode, and weakly pathogenic Xanthomonas arboricola and Pseudomonas cichorii, influence the fate of Xanthomonas and bacterial spot disease severity on tomato. We observed that the outcomes are variable in the mixed infections by co-occurring foliar pathogens, depending on the assemblage of pathogens and timing of colonization (simultaneous infections vs sequential infections), where early-arrival of pathogens altered host susceptibility to subsequent infection by other pathogens through priority effects. Simultaneous infection by root-knot nematodes and foliar Xanthomonas led to overall higher disease severity and compromise in resistance response against nematodes on Mi-resistant tomato varieties. These findings highlight the need to evaluate plant-pathogen interactions in the context of co-occurring pathogens.