Comparative genome analyses suggest a hemibiotrophic lifestyle and virulence differences for the beech bark disease fungal pathogens Neonectria faginata and Neonectria coccinea.

Neonectria faginata and Neonectria coccinea are the causal agents of the insect-fungus disease complex known as beech bark disease (BBD), known to cause mortality in beech forest stands in North America and Europe. These fungal species have been the focus of extensive ecological and disease management studies, yet less progress has been made toward generating genomic resources for both micro- and macro-evolutionary studies. Here, we report a 42.1 and 42.7 mb highly contiguous genome assemblies of N. faginata and N. coccinea, respectively, obtained using Illumina technology. These species share similar gene number counts (12,941 and 12,991) and percentages of predicted genes with assigned functional categories (64 and 65%). Approximately 32% of the predicted proteomes of both species are homologous to proteins involved in pathogenicity, yet N. coccinea shows a higher number of predicted mitogen-activated protein kinase genes, virulence determinants possibly contributing to differences in disease severity between N. faginata and N. coccinea. A wide range of genes encoding for carbohydrate-active enzymes capable of degradation of complex plant polysaccharides and a small number of predicted secretory effector proteins, secondary metabolite biosynthesis clusters and cytochrome oxidase P450 genes were also found. This arsenal of enzymes and effectors correlates with, and reflects, the hemibiotrophic lifestyle of these two fungal pathogens. Phylogenomic analysis and timetree estimations indicated that the N. faginata and N. coccinea species divergence may have occurred at ∼4.1 million years ago. Differences were also observed in the annotated mitochondrial genomes as they were found to be 81.7 kb (N. faginata) and 43.2 kb (N. coccinea) in size. The mitochondrial DNA expansion observed in N. faginata is attributed to the invasion of introns into diverse intra- and intergenic locations. These first draft genomes of N. faginata and N. coccinea serve as valuable tools to increase our understanding of basic genetics, evolutionary mechanisms and molecular physiology of these two nectriaceous plant pathogenic species.

Genome Resources for Thelonectria rubi, the Causal Agent of Nectria Canker of Caneberry.

Thelonectria rubi is the causal agent of Nectria canker of Rubus spp. Here, we report a high-quality draft genome sequence for this pathogen, which also represents the first genome sequence for a Thelonectria species. The genome assembly was 44.6 Mb in size, assembled into 669 scaffolds and consisting of 12,973 predicted protein-coding genes. The availability of genome data for T. rubi provides a critical additional resource for an important plant pathogen and will be useful for fungal biology, comparative genomic, taxonomic and population studies of this and related species.

Exploration of stem endophytic communities revealed developmental stage as one of the drivers of fungal endophytic community assemblages in two Amazonian hardwood genera.

Many aspects of the dynamics of tropical fungal endophyte communities are poorly known, including the influence of host taxonomy, host life stage, host defence, and host geographical distance on community assembly and composition. Recent fungal endophyte research has focused on Hevea brasiliensis due to its global importance as the main source of natural rubber. However, almost no data exist on the fungal community harboured within other Hevea species or its sister genus Micrandra. In this study, we expanded sampling to include four additional Hevea spp. and two Micrandra spp., as well as two host developmental stages. Through culture-dependent and -independent (metagenomic) approaches, a total of 381 seedlings and 144 adults distributed across three remote areas within the Peruvian Amazon were sampled. Results from both sampling methodologies indicate that host developmental stage had a greater influence in community assemblage than host taxonomy or locality. Based on FunGuild ecological guild assignments, saprotrophic and mycotrophic endophytes were more frequent in adults, while plant pathogens were dominant in seedlings. Trichoderma was the most abundant genus recovered from adult trees while Diaporthe prevailed in seedlings. Potential explanations for that disparity of abundance are discussed in relation to plant physiological traits and community ecology hypotheses.

Impact of organic and conventional management on the phyllosphere microbial ecology of an apple crop.

Bacterial communities associated with the phyllosphere of apple trees (Malus domestica cv. Enterprise) grown under organic and conventional management were assessed to determine if increased biological food safety risks might be linked with the bacterial communities associated with either treatment. Libraries of 16S rRNA genes were generated from phyllosphere DNA extracted from a wash made from the surfaces of leaves and apples from replicated organic and conventional treatments. 16S rRNA gene libraries were analyzed with software designed to identify statistically significant differences between bacterial communities as well as shared and unique phylotypes. The identified diversity spanned eight bacterial phyla and 14 classes in the pooled organic and conventional libraries. Significant differences between organic and conventional communities were observed at four of six time points (P < 0.05). Despite the identification of significantly diverse microfloras associated with organic and conventional treatments, no detectable differences in the presence of potential enteric pathogens could be associated with either organic or conventional management. Neither of the bacterial genera most commonly associated with produce-related illness outbreaks (Salmonella and Escherichia) was observed in any of the libraries. The impressive bacterial diversity that was documented in this study provides a valuable contribution to our developing understanding of the total microbial ecology associated with the preharvest phyllospheres of food crops. The fact that organic and conventional phyllosphere bacterial communities were significantly different at numerous time points suggests that crop management methods may influence the bacterial consortia associated with the surfaces of fruits and vegetables.