First report of bacterial blight of Camelina sativa caused by Xanthomonas campestris in Minnesota

Camelina sativa is a short-season Eurasian annual cultivated in Minnesota, USA, as a winter intermediate oilseed crop for sustainable aviation fuel. In June and July of 2025, bacterial blight was observed in breeding trials grown at four MN locations: St. Paul (STP), Rosemont (RMT), Becker (BEC), and Grand Rapids (GRA). The symptoms were initially observed as water-soaked and dark spots on the lower leaves, then turned black with a yellow margin. As the disease progressed, dark lesions began to appear on the stems and seed pods. The severely infected pods were deformed, shriveled, and died prematurely (Fig. S1A, B). Disease incidence ranged from 0 to 30% across the locations. Symptomatic samples from each site were tested positive on the Xanthomonas ImmunoStrip® test (Agdia, Inc), and yellow, viscous colonies with entire margins were isolated on yeast-dextrose-carbonate medium (YDC) from the supernatant of surface sterilized leaf and stem homogenate (Basnet et al. 2024) (Fig. S1.E). A minimum of two isolates were collected from individual plants at each location (2 from STP, 3 from RMT, 4 from BEC, 3 from GRA). To confirm Koch’s postulates, 3-week-old vernalized C. sativa ‘Joelle’ seedlings, grown in a growth chamber (16-h photoperiod, 21°C day/18°C night; n = 9 plants per isolate), were inoculated by piercing the leaf midvein with sterile toothpicks dipped into bacterial suspension (OD600 = 0.1, ~1x108 CFUs/mL) or sterile phosphate buffer saline (mock-inoculated control). Plants were bagged for 48 h to maintain humidity. Two isolates per location and two assay replicates were used for infection assays. At 3 dpi, water-soaked lesions developed in the infected plants, while controls remained healthy (Fig. S1D). By 4 dpi, chlorosis and necrosis appeared; controls showed no symptoms. At 5 dpi, the pathogen was re-isolated. DNA was extracted using DNeasy UltraClean Microbial Kit (Qiagen Inc., Germantown, MD), and a section of the 16S rRNA subunit was sequenced for preliminary genus confirmation using the universal primers 27F (5′-AGAGTTTGATCCTGGCTCAG-3′) and 1492R (5′-TACGGYTACCTTGTTACGACTT-3′). All the sequenced isolates shared >94% identity with Xanthomonas when compared using NCBI BLASTn search. Hybrid Oxford Nanopore Technologies/Illumina sequencing was performed on one isolate per origin (STP XUMN-3, RMT XUMN-4, BEC XUMN-5, GRA: XUMN-6); all four had CheckM values ≥99.6% complete with 0.0% contamination. FastANI analysis (Jain et al., 2018) using complete whole genome sequences of representative Xanthomonas campestris (Xc) strains (Dubrow et al. 2022) and contigs from UW-Madison isolates sequenced as part of their recent first report (Basnet et al. 2024) revealed that these isolates are closely related to those reported to have caused bacterial blight in field pennycress in 2024 in Minnesota (Chiu et al., 2025), as FastANI estimates between them are >98.3%. Additionally, FastANI estimates show >99.0% similarity among camelina isolates and <98.5% similarity to pennycress isolates. While this pattern may suggest a clonal relationship among camelina isolates, this interpretation is based solely on ANI and should be treated as tentative. Camelina has attracted strong interest in the Upper Midwest and the EU for its role in decarbonization and ecosystem services (Berti et al. 2025; Buffi et al. 2026), highlighting the need to monitor emerging pathogens, such as X. campestris, to anticipate economic risks and inform disease management strategies.