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POSTERS: Pathogen dispersal and survival

Aerobiology of Xanthomonas hortorum pv. carotae in carrot seed crops of Central Oregon
Jeremiah Dung - Oregon State University. Jeness Scott- Oregon State University

Bacterial blight of carrot, caused by Xanthomonas hortorum pv. carotae (Xhc), is a common seed-borne disease of carrot. The biennial nature of seed-to-seed carrot seed production requires 13 months from planting to harvesting, resulting in a possible “green bridge” that facilitates Xhc survival from year to year. Consequently, the crop is potentially exposed to bacterial blight inoculum from the seedling stage until harvest. The objective of this research was to quantify airborne Xhc during the potential green bridge period in the biennial carrot seed cropping cycle. Burkard 7-day volumetric spore samplers were used to sample air continuously in three fields harvested in 2018 and two fields intended for harvest in 2019. DNA was extracted from Burkard samples and pooled into weekly samples for a quantitative polymerase chain reaction assay specific to Xhc. Xhc was detected in 52 out of 54 weekly air samples at levels ranging from 102 to 106 bacteria/week. Xhc levels in air samples increased from 102 bacteria/week in July to between 104 and 106 bacteria/week at harvest. In contrast, Xhc levels declined from 105 bacteria/week in August to 103 bacteria/week by November in air samples from one field and varied from 0 to 105 bacteria in air samples from another field. Leaves taken in November showed Xhc populations were between 103 and 104 bacteria/g leaf tissue, demonstrating that sizeable Xhc populations can be established on seed-to-seed carrot fields prior to winter.