© 2003 Plant Management Network.
First Report of Powdery Mildew of Mahonia aquifolium Caused by Microsphaera berberidis (Erysiphe berberidis) in North America
Dean A. Glawe, Plant Pathologist, Puyallup Research and Extension Center, Washington State University, 7612 Pioneer Way East, Puyallup 98371-4998
Corresponding author: Dean A. Glawe. firstname.lastname@example.org
Glawe, D. A. 2003. First report of powdery mildew of Mahonia aquifolium caused by Microsphaera berberidis (Erysiphe berberidis) in North America. Online. Plant Health Progress doi:10.1094/PHP-2003-0206-01-HN.
Mahonia aquifolium (Pursh) Nutt. (syn. Berberis aquifolium Pursh) (Tall Oregon Grape) is a widely-grown plant in the coastal Pacific Northwest (3,4). Prized by landscapers for its holly-like leaves, upright growth habit, colorful berries, and fall foliage (3), it is a native species that was used by Native Americans for food, dye, and medicines (4). This report documents for the first time a powdery mildew on M. aquifolium in North America caused by a fungus fitting the description of Microsphaera berberidis (DC.) Lév. (1).
The most noticeable signs of the disease are whitish patches of mycelium, conidiogenous structures, and conidia typical of a powdery mildew. Younger leaves tend to exhibit the most severe symptoms, and they frequently are stunted (Fig. 1). Characteristics of the fungus include: amphigenous mycelium, primarily on adaxial side of leaf; white to grayish-brown colonies that are effuse to dense and form circular patches that often coalesce to cover the entire leaf surface; and nipple-shaped appressoria (Fig. 2). The anamorph of the fungus displays: conidiophores (Fig. 3) that are straight, with cylindric foot-cells; conidia (Fig. 4) that are generally borne singly, although occasionally adhering in short chains of 2-3 spores, and that are cylindric, generally with rounded ends, measuring (22-) 31-42 (-45) × (6.1-) 9-13 (-14) µm. The teleomorph is absent. A voucher specimen (collection originating from Seattle, King County, Washington) was deposited in the Mycological Herbarium at Washington State University (WSP number 70311).
The fungus described here resembles closely the anamorph of M. berberidis as treated by Braun (1, and references therein). Teleomorphs of powdery mildews seldom are found in western Washington, a situation common in regions with humid or warm climates (1). Braun (1) noted that the teleomorph of M. berberidis is frequently lacking. He listed M. berberidis as occurring on various species of Berberidaceae in Europe, Central Asia, Asia Minor, and South Africa, and he included several species of Mahonia as hosts of this fungus. Thus, it seems reasonable to identify the fungus in this report as M. berberidis. Braun and Takamatsu (2) recently suggested resurrecting the binomial Erysiphe berberidis DC for this fungus. The work they (2) cite to support this transfer provides interesting inferences on the evolution of powdery mildews and implications for genus-level taxonomy. Because Microsphaera is used so extensively in the phytopathogical literature it seems prudent in the present report to use M. berberidis while noting that E. berberidis may become the preferred name for designating this fungus if the nomenclatural change suggested by Braun and Takamatsu (2) becomes accepted by taxonomists. [* see Erratum]
The voucher specimen is from a plant that exhibited conspicuous powdery mildew symptoms for several consecutive years. While the diseased leaves are unsightly, the plant seemed to tolerate the presence of the fungus reasonably well, although this and other infected plants do seem to exhibit less vigor than uninfected plants.
1. Braun, U. 1995. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag.
2. Braun, U., and Takamatsu, S. 2000. Phylogeny of Erysiphe, Microsphaera, Uncinula (Erysipheae) and Cystotheca, Podosphaera, Sphaerotheca (Cystotheceae) inferred from rDNA ITS sequences-some taxonomic consequences. Schlechtendalia 4:1-33.
3. Brenzel, K. N., ed. 1995. Sunset Western Garden Book. Sunset Publishing Corporation, Menlo Park, CA.
4. Pojar, J., and MacKinnon, A., eds. 1994. Plants of the Pacific Northwest Coast. Lone Pine Publishing. Redmond, Washington.