Temporal and Spatial pattern of stigma microbiome and its affiliation with a phytopathogen Erwinia amylovora on apple flower

Flowers are important for agriculture as they are directly linked to reproductive output. The flower disease, such as fire blight, caused by a bacterial phytopathogen Erwinia amylovora on apples and pears and resulted in fruitless. Despite the bacterial community of the plant microbiome colonizing roots and leaves have been acknowledged, the microorganisms inhabited on flowers, especially colonized with a pathogen, has remained poorly understood. Here, we investigated the temporal and spatial pattern of microbial communities affiliated with E. amylovora on stigmas of single apple flowers. Temporal pattern analysis of stigma bacterial communities indicated that microbial diversity increased at the early blossom and decreased at the late blossom. During the flower blooming, Enterobacteriaceae and Pseudomonadaceae predominated Proteobacteria gradually occupied the flowers both absence and presence of E. amylovora. Compared to control, E. amylovora colonization did not affect the diversity but significantly changed the microbioal compositions along flower developmental pattern. Though with the strict experimental control of host and environmental factors, only a proportion of spatial separated flowers developed disease symptoms which harbored heavy absolute abundance of E. amylovora. Taxonomic analysis of community composition showed Proteobacteria phylum dominants these spatial dispersed flowers, which was predominated by representatives of Enterobacteriaceae and Pseudomonadaceae. No specific pattern was observed between the absolute abundance of E. amylovora and community diversity. The observed profile of microbial community and its affiliation with pathogen E. amylovora on flower stigmas improved our understanding of flower microbial ecology and the possible effects of microbes-pathogen-host interaction on flower health.