Fusarioid community structure among conifer nurseries of the contiguous U.S.A. and virulence of conifer-associated Fusarium commune

Abstract

Fusaria can be introduced into novel landscapes through latent-infected nursery stock and cause seedling mortality. Molecular tools can rapidly identify and track Fusarioid pathogens to mitigate novel pathogen introductions by informing both pathogen composition and pathogenicity of different Fusarium spp. Understanding the community structure and population genetics of Fusarium spp. is a prerequisite for developing robust primers to detect pathogenic species. Accessory chromosomes have been identified in fungi that house virulence genes that can be horizontally transferred among species and populations. These accessory chromosomes and/or associated virulence genes are prime targets for developing diagnostic probes to identify conifer pathogens. Fusarium commune is an understudied species that can be pathogenic to both herbaceous crops and timber trees; however, its virulence mechanisms for conifers have not been elucidated. Fusarium annulatum has recently been described as a distinct species from F. proliferatum, a species that is a known pathogen of conifers. Subsequently, F. annulatum virulence to conifers is not well studied. Our work has three objectives: 1) evaluate Fusarioid fungal community structure in conifer nurseries across the U.S.A. by identifying host associations and geographic distributions, 2) evaluate virulence of conifer-associated Fusarioid isolates on ponderosa pine (Pinus ponderosa), loblolly pine (P. taeda), and Douglas-fir (Pseudotsuga menziesii) seedlings, and 3) use genomic tools to identify candidate virulence genes in host-pathogen interactions that allow design of diagnostic primers for rapid identification and tracking of Fusarioid pathogens. In this study, ca. 26 Fusarium spp., including F. commune and F. annulatum, were collected from conifer nurseries. Unique genomic regions and virulence genes of 15 Fusarioid fungal genomes were compared to identify diagnostic primer targets. Further, three conifer-derived F. commune isolates (two from Douglas-fir and one from ponderosa pine) were compared with two non-conifer F. commune isolates [from rice (Oryza sativa) and tomato (Solanum lycopersicum)] to identify genes involved in pathogenicity to conifer hosts (Figure 1). This work will identify virulence factors of Fusarium that determine host specificity and genomic regions for developing tools that quantify the inoculum density of Fusarium pathogen in conifer nurseries and/or track Fusarioid pathogens from nurseries to prevent/monitor their spread into the forest landscape.

Citation

Dobbs, John T.; Kim, Mee-Sook; Reynolds, Gregory; Wilhelmi, Nicholas; Klopfenstein, Ned B.; Stewart, Jane E. 2024. Fusarioid community structure among conifer nurseries of the contiguous U.S.A. and virulence of conifer-associated Fusarium commune. In: Brooks, Rachel K., compiler. Proceedings of the 68th Western International Forest Disease Work Conference; 5-9 June 2023; Rohnert Park, CA. Online: https://www.wifdwc.org. p. 119-120.