Phylogenetic relationships and spatial distributions of putative fungal pathogens of seedlings across a rainfall gradient in Panama

The interaction of climate, plant, and soil factors drives putative soil fungal pathogen diversity and community structure in dry grasslands

Soil pathogens play important roles in shaping soil microbial diversity and controlling ecosystem functions. Though climate and local environmental factors and their influences on fungal pathogen communities have been examined separately, few studies explore the relative contributions of these factors. This is particularly crucial in eco-fragile regions, which are more sensitive to environmental changes. Herein we investigated the diversity and community structure of putative soil fungal pathogens in cold and dry grasslands on the Tibetan Plateau, using high-throughput sequencing. The results showed that steppe soils had the highest diversity of all pathogens and plant pathogens; contrastingly, meadow soils had the highest animal pathogen diversity. Structural equation modelling revealed that climate, plant, and soil had similar levels of influence on putative soil fungal pathogen diversity, with total effects ranging from 52% to 59% (all p < 0.001), with precipitation exhibiting a stronger direct effect than plant and soil factors. Putative soil fungal pathogen community structure gradually changed with desert, steppe, and meadow, and was primarily controlled by the interactions of climate, plant, and soil factors rather than by distinct factors individually. This finding contrasts with most studies of soil bacterial and fungal community structure, which generally report dominant roles of individual environmental factors.

Anamorphic chaetosphaeriaceous fungi from China

Chaetosphaeriaceae is one of the largest families in Sordariomycetes with its members commonly found on decaying leaf, fruit, branch, bark and wood in both terrestrial and submerged environment in nature. This paper reports our research result of diversity, taxonomy and phylogeny of anamorphic Chaetosphaeriaceae in China, which is based on a systematic study with an integrated approach of morphological observation and phylogenetic analysis for a large collection (> 1300 herbarium specimens and 1100 living strains). The family Chaetosphaeriaceae is expanded to accommodate 89 accepted genera, including 22 new genera and 10 newly assigned genera. Most of these genera (except for Chaetosphaeria and several other relatively large genera) are delimitated as monophyletic genera with well-defined diagnostic characters in morphology. The phylogenetic connection of non-phialidic Sporidesmium-like fungi is further confirmed and expanded to 10 different genera. The polyphyletic Codinaea/Dictyochaeta/Tainosphaeria complex is further resolved with a taxonomic framework of 28 monophyletic genera by redelimitation of Codinaea and Dictyochaeta with narrower concept, acceptance of the 16 established genera, and finally introduction of 10 new genera. Chloridium is phylogenetically redefined as monophyletic genus with narrower concept as typified by the type species, but a systematic review in both generic and species level is still needed. For biodiversity of chaetosphaeriaceous fungi, a total of 369 species in 76 genera, including 119 new species, 47 new combinations, and one new name, are documented. The identification keys are provided for most genera, especially the large genera such as Codinaea s. str., Codinaeella, Stilbochaeta, Cryptophiale, Thozetella, Dinemasporium and Pseudolachnella. In addition, ten known species were excluded from the family and reclassified. Systematic revision of several relatively large polyphyletic genera should be conducted in future studies, including Bahusutrabeeja, Ellisembia, Stanjehughesia, Cacumisporium, Chaetosphaeria, Chloridium, Craspedodidymum, Cryptophiale, Cryptophialoidea, Dictyochaetopsis, Minimidochium, and many published species of Codinaea and Dictyochaeta.

Host-generalist fungal pathogens of seedlings may maintain forest diversity via host-specific impacts and differential susceptibility among tree species

Host-specialized pathogens are credited with the maintenance of tropical forest diversity under the Janzen-Connell hypothesis. Yet, in diverse forests, selection may favor pathogens with broad host ranges, given their passive dispersal and the relative rarity of tree species. We surveyed the host associations of potential pathogens isolated from symptomatic seedlings in forests in Panama and used inoculations to assess the pathogenicity and host ranges of 27 fungal isolates, and differences among tree species in susceptibility. Thirty-one of the 33 nonsingleton operational taxonomic units (OTUs) isolated from seedlings are multi-host. All 31 multi-host OTUs exhibit low to moderate specialization, and we observed phylogenetically overdispersed host use for 19 OTUs. The pathogenicity of 10 isolates was experimentally confirmed; nine caused disease in seedlings in multiple families. However, the outcome of infection differs among tree species susceptible to a given multi-host pathogen. Furthermore, some tree species were seemingly resistant to all fungi tested, while others were susceptible to multiple fungi. Tree species adapted to environments with lower disease pressure were most likely to exhibit disease. Our results suggest that generalist pathogens contribute to the maintenance of local and regional forest diversity via host-specific impacts and the exclusion of disease-sensitive trees from disease-prone habitats.

Habitat type and interannual variation shape unique fungal pathogen communities on a California native bunchgrass

The role of infectious disease in regulating host populations is increasingly recognized, but how environmental conditions affect pathogen communities and infection levels remains poorly understood. Over 3 y, we compared foliar disease burden, fungal pathogen community composition, and foliar chemistry in the perennial bunchgrass Stipa pulchra occurring in adjacent serpentine and nonserpentine grassland habitats with distinct soil types and plant communities. We found that serpentine and nonserpentine S. pulchra experienced consistent, low disease pressure associated with distinct fungal pathogen communities with high interannual species turnover. Additionally, plant chemistry differed with habitat type. The results indicate that this species experiences minimal foliar disease associated with diverse fungal communities that are structured across landscapes by spatially and temporally variable conditions. Distinct fungal communities associated with different growing conditions may shield S. pulchra from large disease outbreaks, contributing to the low disease burden observed on this and other Mediterranean grassland species.

Root pathogen diversity and composition varies with climate in undisturbed grasslands, but less so in anthropogenically disturbed grasslands

Soil-borne pathogens structure plant communities, shaping their diversity, and through these effects may mediate plant responses to climate change and disturbance. Little is known, however, about the environmental determinants of plant pathogen communities. Therefore, we explored the impact of climate gradients and anthropogenic disturbance on root-associated pathogens in grasslands. We examined the community structure of two pathogenic groups-fungal pathogens and oomycetes-in undisturbed and anthropogenically disturbed grasslands across a natural precipitation and temperature gradient in the Midwestern USA. In undisturbed grasslands, precipitation and temperature gradients were important predictors of pathogen community richness and composition. Oomycete richness increased with precipitation, while fungal pathogen richness depended on an interaction of precipitation and temperature, with precipitation increasing richness most with higher temperatures. Disturbance altered plant pathogen composition and precipitation and temperature had a reduced effect on pathogen richness and composition in disturbed grasslands. Because pathogens can mediate plant community diversity and structure, the sensitivity of pathogens to disturbance and climate suggests that degradation of the pathogen community may mediate loss, or limit restoration of, native plant diversity in disturbed grasslands, and may modify plant community response to climate change.

Laboratory diagnostics, phylogenetic analysis and clinical outcome of a subcutaneous Mycoleptodiscus indicus infection in an immunocompetent cat

Background

Mycoleptodiscus indicus is a dematiaceous hyphomycete fungus found on plant leaves. It has been rarely reported as a cause of human or animal disease, possibly because it is difficult to culture and identify from clinical specimens. Infections are presumably acquired by traumatic implantation.

Case presentation

An 8-year-old non-immunosuppressed cat from Georgia, USA, presented with a left front leg swelling without lameness. Cytology from a fine needle aspirate revealed pyogranulomatous inflammation with both cytoplasmic and extracellular fungal elements. There were septate hyphae with irregularly sized segments, non-staining uneven walls, and rounded yeast-like forms from which longer hyphae arose in a hub-and-spoke pattern. A mold was isolated on agar from a fine needle aspirate collected 1 week later and identified as M. indicus by morphology, DNA sequencing and phylogenetic analysis. The cat recovered completely and uneventfully with antifungal treatment.

Conclusions

We report a previously undescribed presentation of M. indicus causing a subcutaneous infection in a cat with successful antifungal treatment. In this study we highlight the potential of M. indicus to infect immunocompetent animals, and the veterinary medical community should be aware of its unusual but characteristic clinical, microbiological and cytologic presentation.