Genetic and Pathogenic Relatedness of Pseudoperonospora Cubensis and P. Humuli
Mycology Genetic and Pathogenic Relatedness of Pseudoperonospora cubensis and P. humuli Melanie N. Mitchell, Cynthia M. Ocamb, Niklaus J. Grünwald, Leah E. Mancino, and David H. Gent First, second, and fourth authors: Department of Botany and Plant Pathology, third author: United States Department of Agriculture– Agricultural Research Service (USDA-ARS), Horticultural Crops Research Unit; and fifth author: USDA-ARS, Forage Seed and Cereal Research Unit, and Department of Botany and Plant Pathology, Oregon State University, Corvallis. Accepted for publication 6 March 2011. ABSTRACT Mitchell, M. N., Ocamb, C. M., Grünwald, N. J., Mancino, L. E., and in nuclear, mitochondrial, and ITS phylogenetic analyses, with the Gent, D. H. 2011. Genetic and pathogenic relatedness of Pseudoperono- exception of isolates of P. humuli from Humulus japonicus from Korea. spora cubensis and P. h u m u l i . Phytopathology 101:805-818. The P. cubensis isolates appeared to contain the P. humuli cluster, which may indicate that P. h um u li descended from P. cubensis. Host-specificity The most economically important plant pathogens in the genus experiments were conducted with two reportedly universally susceptible Pseudoperonospora (family Peronosporaceae) are Pseudoperonospora hosts of P. cubensis and two hop cultivars highly susceptible to P. humuli. cubensis and P. hu m u li, causal agents of downy mildew on cucurbits and P. cubensis consistently infected the hop cultivars at very low rates, and hop, respectively. Recently, P. humuli was reduced to a taxonomic sporangiophores invariably emerged from necrotic or chlorotic hyper- synonym of P. cubensis based on internal transcribed spacer (ITS) sensitive-like lesions. Only a single sporangiophore of P.
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