First Report of the Powdery Mildews Leveillula taurica and Podosphaera pannosa on Rose Periwinkle in the United States

In April 2013, unthrifty rose periwinkle (Catharanthus roseus (L.) G. Don) from a residential garden in Mililani, HI, was sent to the Hawaii Department of Agriculture. Symptoms, present on all plants, included leaf chlorosis, defoliation, and premature flower drop with necrotic spots on the adaxial side of leaves corresponding to patches of grayish mildew-like growth on the abaxial side. Samples were collected and sent to USDA PPQ National Identification Services (NIS) for confirmation. At NIS, stereoscope examination of the plants revealed two distinct powdery mildews. One, on the stems and leaves, had dimorphic conidia, with lanceolate primary (54 to 72 × 14 to 22 μm) and cylindrical secondary conidia (49 to 75 × 11 to 21 μm) (n = 25 for each), both with a reticulate surface. This fungus was identified morphologically as Leveillula taurica (Lév.) G. Arnaud (1). The second powdery mildew appeared confined to the sepals and petals. The external hyphae of this fungus produced upright chains of cylindrical to ovoid conidia (up to eight per chain), which contained fibrosin bodies and measured 22 × 12 μm (n = 50) with straight foot cells averaging 43 μm long, placing this fungus in the genus Podosphaera Kunze (1). Plants containing both fungi were accessioned as BPI892677 in the US National Fungal Collection. For molecular characterization, genomic DNA of the Podosphaera was obtained by scraping conidia from a petal and extracting with Thermo Scientific's Lyse and Go PCR Reagent. DNA of the Leveillula was extracted from 5 mm of infected leaf using Qiagen's Plant mini kit. The ITS region of each fungus was amplified and sequenced directly with primers ITS1F and ITS4. Each consensus sequence was created from manually edited chromatograms, searched against NCBI's GenBank using MegaBLAST and phylogenetically analyzed in MEGA5.2 under maximum parsimony (MP) in context with most similar hits and representatives from phylogenetic studies (2,3). Sequences from types of these fungi are not available for comparison. The resulting Podosphaera phylogeny grouped the Podosphaera suspect (GenBank KF703448) within a clade of P. pannosa (e.g., AB525938; bootstrap = 90). The Leveillula phylogeny grouped the Leveillula suspect (KF703447) within a clade (bootstrap = 88) of L. taurica (e.g., AB044346), L. chrozophorae (AB044346), and L. elaeagni (AB048350). Although the ITS sequences of these taxa are phylogenetically indistinguishable, morphological characters differentiate each