Analysis of digitized herbarium records and community science observations provides a glimpse of downy mildew diversity of North America and importance of continued digitization and collecting

Authors: DAVIS, WILLIAM - Orise Fellow; Crouch, Jo Anne

Submitted to: Fungal Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2021
Publication Date: 12/1/2021
Citation: Davis, W.J., Crouch, J.A. 2021. Analysis of digitized herbarium records and community science observations provides a glimpse of downy mildew diversity of North America and importance of continued digitization and collecting. Fungal Ecology. 55:101126. https://doi.org/10.1016/j.funeco.2021.101126.
DOI: https://doi.org/10.1016/j.funeco.2021.101126

Interpretive Summary: Downy mildew diseases cause significant crop losses globally. Herbarium collections provide an opportunity to develop a baseline census of the downy mildews that reside in North America; however, these resources are based on opportunistic collecting efforts, which might limit their usefulness. In this study, we analyzed the MyCoPortal digitized herbarium records of downy mildew specimens collected in North America between 1800 to present day. The majority of the collections came from the U.S., and 90% of all collections were made prior to the 1960s. Only 28% of the known downy mildews were present in the collections, and we identified 50–100 potentially undescribed species. Together, these results highlight the need for new and continued downy mildew collections, taxonomic research and digitization efforts. This information will be useful for mycologists and plant pathologists working to understand the distribution and diversity of downy mildews.

Technical Abstract: Downy mildew diseases caused by Peronosporaceae cause significant crop losses globally, with several emerging and resurgent threats in recent decades. Biodiversity data from digitized herbarium specimens provide an opportunity to develop a baseline census of species diversity, however, these resources are aggregations of nonrandom and opportunistic collecting efforts, which could lead to spurious results. Here, the MyCoPortal census of digitized herbarium records for downy mildew species collected from North America 1800 to present were analyzed. From 9838 unique records, 196 species were identified, reflecting just ~28% of known species diversity. Temporal and geographic collecting biases were observed, with 90% of the collections made prior to the 1960s and the efforts of six “super-collectors” accounting for 25% of the collections. The presence of 50–100 undescribed species in North America was inferred from the records. Together, these results highlight the need for continued downy mildew collections, taxonomic research and digitization efforts.