Cruciferous Weeds Do Not Act as Major Reservoirs of Inoculum for Black Rot Outbreaks in New York State.

Cruciferous weeds have been shown to harbor diverse pathovars, including the agronomically damaging black rot of cabbage pathogen, pv. However, the importance of weeds as inoculum sources for pv. outbreaks in New York remains unknown. To determine if cruciferous weeds act as primary reservoirs for pv. , fields that were rotating between cabbage or had severe black rot outbreaks were chosen for evaluation. Over a consecutive 3-year period, 148 cruciferous and noncruciferous weed samples were collected at 34 unique sites located across five New York counties. Of the 148 weed samples analyzed, 48 isolates were identified, with a subset characterized using multilocus sequence analysis. All isolates originated from weeds belonging to the Brassicaceae family, with predominant weed hosts being shepherd's purse (), wild mustard (), yellow rocket (), and pennycress (). Identifying pathogenic weed isolates was rare, with only eight isolates causing brown necrotic leaf spots or typical V-shaped lesions on cabbage. There was no evidence of cabbage-infecting weed isolates persisting in an infected field by overwintering in weed hosts; however, similar cabbage and weed haplotypes were identified in the same field during an active black rot outbreak. weed isolates are genetically diverse both within and between fields, but our findings indicate that weed isolates do not appear to act as primary sources of inoculum for fields in New York.