Influence of Co-occurring Weakly Pathogenic Bacterial Species on Bacterial Spot Disease Dynamics on Tomato.

Mixed infections caused by multiple pathogenic and weakly pathogenic strains inhabiting the same host plants are common in nature and may modify pathogen dynamics. However, traditional plant pathogen studies have mostly focused on the binary interaction between a single host and a single pathogen. In this study, we have looked beyond this binary interaction and evaluated the impact of coinfection on disease dynamics on tomato using the bacterial spot pathogen (), the co-occurring weakly pathogenic strain of (), and the co-occurring potential weak pathogenic strain of (). Time-series coinfection experiments monitoring disease severity and within-host population dynamics revealed higher disease severity in coinfection by three species compared with infection by alone. However, coinfection by dual species, and , or resulted in lower disease severity compared with alone. Thus, coinfection outcomes depend on interacting species. Weak pathogens could exploit to colonize the host plant as indicated by their higher populations in coinfection. However, population dynamics were dependent on the coinfecting partner. While resource competition might be a possible explanation for lower population in dual coinfection, interaction of with the host was found to influence population. Interestingly, population was higher in the presence of three-species interaction compared with and coinfection, suggesting potential modulation of cooperative interactions among and in three-species coinfection rather than competitive interactions. Humidity played a significant role in population dynamics of the three species. Overall, this study highlighted the importance of coinfection dynamics in studying plant disease outbreaks.