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First Report of Bacterial Blight of Peony Caused by Xanthomonas hortorum in Ohio

    Authors and Affiliations
    • T. L. Klass1
    • J. J. Long2
    • J. A. Summers2
    • V. Roman-Reyna2
    • R. Koebnik3
    • J. M. Jacobs1
    • F. Peduto Hand2
    1. 1Department of Plant Pathology and Infectious Disease Institute, The Ohio State University, Columbus, OH 43210, U.S.A.
    2. 2Department of Plant Pathology, The Ohio State University, Columbus, OH 43210, U.S.A.
    3. 3Institut de Recherche pour le Développement, UMR Interactions Plantes Microorganismes Environnement, Montpellier, France

    Ohio is one of the top five producers of floriculture crops in the United States (USDA 2016). As a result, the detection and diagnosis of diseases impacting floriculture crops in Ohio, such as peony, is of high importance for the industry. In May 2013, leaves from 20% of approximately 250 Paeonia ‘Paula Fay’ plants in a commercial nursery in northeastern Ohio displayed necrotic, dark purple lesions. Two symptomatic plants were submitted to The Ohio State University Plant and Pest Diagnostic Clinic for diagnosis and analysis. Microscopic observation revealed bacterial streaming from symptomatic leaf lesions. Yellow-pigmented, mucoid, convex colonies typical of Xanthomonas were recovered from the lesion margins on yeast extract dextrose CaCO3 agar plates after incubation at 28°C for 3 days. To identify this bacterial isolate, DNA was extracted from single colonies of purified cultures and sequenced with an Illumina platform using the NEBNext Ultra II DNA Library preparation kit with TruSeq adapters. Average nucleotide identity (ANI) analysis was performed with the ANI-Matrix software Enveomics tool (Rodriguez-R and Konstantinidis 2016) using the sequenced genome (NCBI GenBank Biosample no. SAMN11831455). The identified bacterium was determined to be Xanthomonas hortorum when compared with other Xanthomonas species (hortorum, gardneri, euvesicatoria, and vesicatoria), as it had a 96% ANI with other X. hortorum. Multiple alignment of the sequenced gyrB fragment showed that this peony isolate was 100% identical to the peony-isolated Xanthomonas sp. reported in Virginia in 2012 (GenBank accession no. JX436475.1; Oliver et al. 2012; Parkinson et al. 2009). For Koch’s postulates, six individual leaves per plant from three Paeonia lactiflora ‘Sarah Bernhardt’ plants were infiltrated with 1 ml of a phosphate-buffered saline (PBS) bacterial suspension (5.3 × 108 CFU/ml) using a blunt syringe. Eight individual control leaves per plant from three control plants were similarly inoculated with PBS and compared with the bacterial treatment. Peony plants were maintained in a greenhouse at an average of 22°C and were covered with clear plastic bags for 2 days following inoculation to increase humidity and favor infection. Slight chlorosis was visible on leaves infiltrated with the bacterial suspension starting 7 days postinoculation (dpi). At 20 dpi, the chlorosis was much more pronounced. In contrast, no chlorosis or other symptoms were observed on the PBS-infiltrated control leaves. After 3 months of incubating in the greenhouse, the treated leaves developed purple spotting, likely as a result of the longer days and warmer weather. Bacterial infiltrations were repeated once using new peony plants maintained in a growth chamber at 23°C and 70% relative humidity. Purple leaf blight symptoms were pronounced after 1 week and progressed quickly. To complete Koch’s postulates, bacteria were reisolated from both the greenhouse and growth chamber treated plants and confirmed to be Xanthomonas through colony characteristics and 16S PCR and sequencing using primers E9F/E1541R (Baker et al. 2003). This is the first report of X. hortorum on peony in Ohio, which has implications for Ohio peony producers. In the near future, pathogen-specific primers will be designed so that diagnostic clinics can easily identify this peony pathogen and advise producers on how to best prevent and manage it.

    The author(s) declare no conflict of interest.


    The author(s) declare no conflict of interest.