Characterizing Aerial Dispersal of Xanthomonas hortorum pv. carotae in Central Oregon Carrot Seed Production Systems During Harvest

Xanthomonas hortorum pv. carotae (Xhc) is a plant-pathogenic bacterium that causes bacterial blight of carrot. It impacts international trade due to little to no tolerance for the pathogen in carrot seed. Because the biennial crop has overlapping growing seasons and Xhc has been detected in the air in areas of carrot seed production, an improved understanding of the dispersion pathways is needed. Experiments (Airborne Xanthomonas Experiments- Madras [AXE-M]) conducted in central Oregon were designed to characterize the airborne transport and deposition of particles dispersing Xhc during harvest events. Debris samples were collected with a novel passive sampling device, the Cascade Settling Trap (CST), that sorted particles into size classes of interest as the particles were deposited out of the air column. CSTs were used during one harvest event in 2021 and three in 2022. Negative binomial regression analysis conducted on data collected in 2022 indicated that particle size and the distance from which particles were sampled can be predictive of the amount of Xhc detected. Burkard samplers were utilized in 2021 and 2022 to quantify airborne Xhc during the growing season and specific events of interest. Meteorological data, in conjunction with the use of optical particle counters, allowed for estimation of real-time airborne particle concentrations and their potential for transport. By developing a more detailed understanding of the aerobiology of Xhc, better risk assessment tools and pathogen management strategies can be employed to assess the potential for these particles to disperse Xhc across varying scales.