First Report of Downy Mildew Caused by Plasmopara halstedii on Black-eyed Susan (Rudbeckia fulgida cv. 'Goldsturm') in Maryland.

摘要: The North American perennial black-eyed Susan (Rudbeckia fulgida cv. Goldsturm) is an important nursery crop, prized by gardeners and landscapers for its persistent bloom ease of cultivation. In September 2013, disease symptoms characteristic downy mildew were observed from multiple R. plants at two commercial nurseries in the Maryland counties Howard Anne Arundel. Over 100 affected this both nurseries, rendering unmarketable causing a substantial financial loss. Plants exhibited dark necrotic lesions on adaxial leaf surface, sporulating masses white mycelium abaxial surface extreme infections. stunted with reduced number blooms. Microscopic visualization showed coenocytic mycelium, hyaline sporangiophores (length 261 to 904 μm; = 557 n 20) that straight monopodially branched right angles several terminal branchlets. Sporangia hyaline, ovoid ellipt...