Summary Large populations of bacteria live on leaf surfaces and these phyllosphere bacteria can have important effects on plant health. However, we currently have a limited understanding of bacterial diversity on tree leaves and the inter- and intra-specific variability in phyllosphere community structure. We used a bar-coded pyrosequencing technique to characterize the bacterial communities from leaves of 56 tree species in Boulder, Colorado, USA, quantifying the intra- and inter-individual variability in the bacterial communities from 10 of these species. We also examined the geographic variability in phyllosphere communities on Pinus ponderosa from several locations across the globe. Individual tree species harboured high levels of bacterial diversity and there was considerable variability in community composition between trees. The bacterial communities were organized in patterns predictable from the relatedness of the trees as there was significant correspondence between tree phylogeny and bacterial community phylogeny. Inter-specific variability in bacterial community composition exceeded intra-specific variability, a pattern that held even across continents where we observed minimal geographic differentiation in the bacterial communities on P. ponderosa needles.

Succession is a widely studied process in plant and animal systems, but succession in microbial communities has received relatively little attention despite the ubiquity of microorganisms in natural habitats. One important microbial habitat is the phyllosphere, or leaf surface, which harbors large, diverse populations of bacteria and offers unique opportunities for the study of succession and temporal community assembly patterns. To explore bacterial community successional patterns, we sampled phyllosphere communities on cottonwood (Populus deltoides) trees multiple times across the growing season, from leaf emergence to leaf fall. Bacterial community composition was highly variable throughout the growing season; leaves sampled as little as a week apart were found to harbor significantly different communities, and the temporal variability on a given tree exceeded the variability in community composition between individual trees sampled on a given day. The bacterial communities clearly clustered into early-, mid-, and late-season clusters, with early- and late-season communities being more similar to each other than to the mid-season communities, and these patterns appeared consistent from year to year. Although we observed clear and predictable changes in bacterial community composition during the course of the growing season, changes in phyllosphere bacterial diversity were less predictable. We examined the species-time relationship, a measure of species turnover rate, and found that the relationship was fundamentally similar to that observed in plant and invertebrate communities, just on a shorter time scale. The temporal dynamics we observed suggest that although phyllosphere bacterial communities have high levels of phylogenetic diversity and rapid turnover rates, these communities follow predictable successional patterns from season to season.

Phytophthora, with 203 species, is a genus of high importance in agriculture worldwide. Here we present the online resource "IDphy" (Link) developed to facilitate the correct identification of species of Phytophthora using the type specimens from the original descriptions wherever possible. IDphy emphasizes species of high economic impact and regulatory concern for the United States. IDphy presents an interactive Lucid key and a tabular key for 161 culturable species described as of May 2018, including 141 ex-types and 20 well-authenticated specimens. IDphy contains SOPs for morphological and molecular characterization, as well as a glossary, image gallery, and numerous links. Each of the 161 factsheets includes access to nomenclature, morphological and molecular features, including sequences of ITS rDNA, COI (barcoding genes), YPT1, β-tub, EF1α, L10, HSP90 and other genes. IDphy contains an innovative in silico BLAST and phylogenetic sequence analysis using NCBI. The IDphy Mobile App, released in August 2021 (free for Android or iOS) (Link) allows users to take the Lucid key into the laboratory. IDphy is the first online identification tool based on the ex-types implemented for plant pathogens. In this manuscript, we also include information for 21 new species and one hybrid described after the publication of IDphy, the status of the specimens of the Types and ex-types at international herbaria and culture collections, and the status of genomes at the GenBank (currently 153 genome assemblies which correspond to 42 described species including 16 ex-types). The model's effectiveness of the IDphy online resource and the content of this manuscript could inspire other researchers to develop additional identification tools for other important groups of plant pathogens.