High incidence of <i>Hyaloperonospora cardamines</i>‐<i>laciniatae</i> on <i>Cardamine concatenata</i> in Maryland, USA

In May 2022, a heavily diseased patch of the spring ephemeral, Cardamine concatenata, was observed in Gambrill State Park (39.46425° N, 77.49221° W) Frederick County, Maryland, USA. Symptoms included necrotic patches delimited by veins, with variable chlorosis (Fig. 1). Sparse grey sporulation visible on abaxial leaf surface. Disease incidence 10 × 20 m 100% and severity – individual plants. Morphological examination found hyaline, ovate sporangia (average 18.3 ×15.6 μm, length:width 1.18) borne singly curved to slightly sterigmata, typically arising from paired branchlets (Figs. 2, 3). Branchlets (mean 7.1 μm wide) extended sporangiophores mean primary width 11.7 μm. Oospores diameter 35.9 μm) were prominent cleared foliar tissue 4). Based these characteristics, geography, host, Hyaloperonospora cardamines-laciniatae hypothesised (Voglmayr et al., 2014). A voucher specimen deposited U.S. National Fungus Collection (BPI 911234). To confirm pathogen identity, DNA extracted 10–20 (FastDNA kit; MP Biomedicals, USA). Three regions (ITS, LSU cox2) amplified using DC6-ITS4 followed ITS4-ITS6 (Cooke 2000) semi-nested reaction; LR0R LR5 (Vilgalys & Hester, 1990); Cox2-F Cox2-R (Hudspeth 2000), respectively. Amplicons cleaned (ExoSAP-IT; Applied Biosystems, USA) bidirectionally sequenced (Eurofins Inc., Blastn analysis determined that obtained sequences had closest identity H. (Table Although downy mildew species are increasingly described narrow, one pathogen-one host concept, our data available literature indicate has at least three hosts, C. diphylla, laciniata (Goker 2004; Voglmayr concatenata is native understory plant eastern forests which above-ground parts only present for two months year. Native butterflies (Pieris spp.) depend spp. foliage complete their lifecycle (Augustine Kingsolver, 2018). It unknown whether this site would influence longevity or suitability Pieris oviposition. The earliest reports Iowa (1903) Ohio, USA (1908; Constantinescu, 1992). More recent diphylla 2003 2014; Voglmayr, pers. comm.). This first report cardamines-laciniatae-induced disease critical butterflies. research supported Department Agriculture, Agricultural Research Service. USDA an equal opportunity provider employer.