Mosaic fungal individuals have the potential to evolve within a single generation

A Metagenomic Survey of Wood Decay Fungi in the Urban Trees of Singapore

Mature tropical urban trees are susceptible to root and trunk rot caused by pathogenic fungi. A metagenomic survey of such fungi was carried out on 210 soil and tissue samples collected from 134 trees of 14 common species in Singapore. Furthermore, 121 fruiting bodies were collected and barcoded. Out of the 22,067 OTUs (operational taxonomic units) identified, 10,646 OTUs had annotation information, and most were either ascomycetes (63.4%) or basidiomycetes (22.5%). Based on their detection in the diseased tissues and surrounding soils and/or the presence of fruiting bodies, fourteen basidiomycetes (nine Polyporales, four Hymenochaetales, one Boletales) and three ascomycetes (three species of Scytalidium) were strongly associated with the diseased trees. Fulvifomes siamensis affected the largest number of tree species surveyed. The association of three fungi was further supported by in vitro wood decay studies. Genetic heterogeneity was common in the diseased tissues and fruiting bodies (Ganoderma species especially). This survey identified the common pathogenic fungi of tropical urban trees and laid the foundation for early diagnosis and targeted mitigation efforts. It also illustrated the complexity of fungal ecology and pathogenicity.

A Nuclei-Based Conceptual Model of (Eco)evolutionary Dynamics in Fungal Heterokaryons

Filamentous fungi are characterised by specific features, such as multinuclearity, coexistence of genetically different nuclei and nuclear movement across the mycelial network. These attributes make them an interesting, yet rather underappreciated, system for studying (eco)evolutionary dynamics. This is especially noticeable among theoretical studies, where rather few consider nuclei and their role in (eco)evolutionary dynamics. To encourage such theoretical approaches, we here provide an overview of existing research on nuclear genotype heterogeneity (NGH) and its sources, such as mutations and vegetative non-self-fusion. We then discuss the resulting intra-mycelial nuclear dynamics and the potential consequences for fitness and adaptation. Finally, we formulate a nuclei-based conceptual framework, which considers three levels of selection: a single nucleus, a subpopulation of nuclei and the mycelium. We compare this framework to other concepts, for example those that consider only the mycelium as the level of selection, and outline the benefits of our approach for studying (eco)evolutionary dynamics. Our concept should serve as a baseline for modelling approaches, such as individual-based simulations, which will contribute greatly to our understanding of multilevel selection and (eco)evolutionary dynamics in filamentous fungi.

Evolution via somatic genetic variation in modular species

Somatic genetic variation (SoGV) may play a consequential yet underappreciated role in long-lived, modular species among plants, animals, and fungi. Recent genomic data identified two levels of genetic heterogeneity, between cell lines and between modules, that are subject to multilevel selection. Because SoGV can transfer into gametes when germlines are sequestered late in ontogeny (plants, algae, and fungi and some basal animals), sexual and asexual processes provide interdependent routes of mutational input and impact the accumulation of genetic load and molecular evolution rates of the integrated asexual/sexual life cycle. Avenues for future research include possible fitness effects of SoGV, the identification and implications of multilevel selection, and modeling of asexual selective sweeps using approaches from tumor evolution.

Epidemiology, Biotic Interactions and Biological Control of Armillarioids in the Northern Hemisphere

Armillarioids, including the genera Armillaria, Desarmillaria and Guyanagaster, represent white-rot specific fungal saprotrophs with soilborne pathogenic potentials on woody hosts. They propagate in the soil by root-like rhizomorphs, connecting between susceptible root sections of their hosts, and often forming extended colonies in native forests. Pathogenic abilities of Armillaria and Desarmillaria genets can readily manifest in compromised hosts, or hosts with full vigour can be invaded by virulent mycelia when exposed to a larger number of newly formed genets. Armillaria root rot-related symptoms are indicators of ecological imbalances in native forests and plantations at the rhizosphere levels, often related to abiotic environmental threats, and most likely unfavourable changes in the microbiome compositions in the interactive zone of the roots. The less-studied biotic impacts that contribute to armillarioid host infection include fungi and insects, as well as forest conditions. On the other hand, negative biotic impactors, like bacterial communities, antagonistic fungi, nematodes and plant-derived substances may find applications in the environment-friendly, biological control of armillarioid root diseases, which can be used instead of, or in combination with the classical, but frequently problematic silvicultural and chemical control measures.