Geographical and seasonal dynamics and air trajectory modeling of air-borne cereal rust fungi: a case study in western Canada

Cereal rust diseases are caused by Puccinia spp. urediniospores that travel by air currents to cause losses in wheat, oat, barley, and rye. In western Canada, inoculum can arrive from the USA through the Great Plains or via a Pacific corridor west of the Rocky Mountains. In addition, climate and land use are known factors in Puccinia dissemination but their relative effects remain poorly understood. We investigated aeromycobiota in western Canada by weekly air-sampling over four growing seasons (2015-2018) three mixed-crop sites in British Columbia and one season (2018) at five Alberta sites. Metabarcoding via rust fungus-enhanced ITS2 amplicon generation and sequencing of sampled air-borne fungi and novel bioinformatic comparative analyses to known, especially curated cereal rust fungal sequences, was used for species identification. Focusing on plant pathogens and particularly cereal rust fungi, we correlated geographical and seasonal dynamics of rust communities with various climatic and land-use drivers. In addition, forward and reverse trajectory HYSPLIT model simulations were used to explore the potential sources of rust urediniospores and their pathways of movement modulated by air currents, through which some pronounced changes in the abundance of wheat rust pathogens were explained. This study paves the way for a potential application for pathogen monitoring and disease risk forecasting as part of the design and development of an early-warning system for enhanced biovigilance to crop diseases.