Detection and Occurrence of Airborne <i>Xanthomonas hortorum</i> pv. <i>carotae</i> in Carrot Seed Production Systems

Bacterial blight of carrot, caused by the plant pathogenic bacterium <i>Xanthomonas hortorum</i> pv. <i>carotae</i> (<i>Xhc</i>), is an important disease of carrot and carrot seed crops. Previous research demonstrated that airborne <i>Xhc</i> could be detected up to 1.6 km downwind of carrot seed fields being harvested, but more research is needed to identify dispersal periods of the pathogen during all stages of carrot seed production. The objective of this research was to quantify and characterize temporal dynamics of airborne <i>Xhc</i> during a biennial seed-to-seed carrot seed production season. During the 2018-2019 season, a Burkard volumetric air sampler was used to collect air samples on a total of 263 and 274 days in a carrot seed crop in each of two fields in central Oregon. Tape samples from the Burkard spore traps were subsequently subjected to a quantitative PCR assay to determine the number of <i>Xhc</i> genomes captured on a daily basis. <i>Xhc</i> was detected on 216 (82.1%) and 228 (83.2%) of sampling days, respectively. On average, 2.67 x 10³ and 4.28 x 10³ <i>Xhc</i> genomes/day were detected in the two fields over the period of sampling. The results from this study suggest that airborne <i>Xhc</i> inoculum likely contribute to the annual and apparently endemic presence of <i>Xhc</i> on carrot seed crops in the region.