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2003 Plant Management Network.
Accepted for publication 29 September 2003. Published 23 October 2003.


First Report of Powdery Mildew of Nandina domestica Caused by Microsphaera berberidis (Erysiphe berberidis) in the Pacific Northwest


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. glawe@wsu.edu


Glawe, D. A. 2003. First report of powdery mildew of Nandina domestica caused by Microsphaera berberidis (Erysiphe berberidis) in the Pacific Northwest. Online. Plant Health Progress doi:10.1094/PHP-2003-1023-01-HN.


Nandina domestica Thunb. (Berberidaceae) is a bamboo-like landscape plant grown widely in the Pacific Northwest. In 2000 through 2002, powdery mildew was observed on 17 landscape plants of N. domestica in cities in the Puget Sound region of western Washington. Diseased plants were collected from Seattle, Bothell, and Edmonds (King County); Everett and Brier (Snohomish County); and Gig Harbor and Tacoma (Pierce County). Microscopic features of the fungus present in these specimens fit those of Microsphaera berberidis (DC) Lv., previously reported from this host species in Scotland (4) and California (5), and on Mahonia aquifolium (Pursh) Nutt. (3). This report documents the presence of this fungus on N. domestica in the Pacific Northwest.

Conspicuous signs of the pathogen included white-colored patches on infected leaves composed of mycelium, conidiogenous structures, and conidia typical of a powdery mildew. Plants with green leaves sometimes, but not always, also developed reddish areas within infected parts of leaves. Such symptoms were not detectable on plants with leaves that were naturally reddish-colored. Characteristics of the fungus were as follows: Mycelium was amphigenous, primarily on the adaxial leaf surface; colonies were effuse or relatively dense (Fig. 1), often coalescing, and usually were white but became grayish to brown; appressoria (Fig. 2) were simple to nipple-shaped or lobed. Conidiophores (Fig. 3) included cylindric foot-cells that measured (19.5-) 20.5-28 (-31) (4.5-) 5-8 m; two to three cells occurred between the foot cell and the developing conidium. Conidia (Fig. 4) were borne singly although they sometimes appeared to be in chains of two to three spores if they failed to detach following maturation. Conidia were cylindric, generally with rounded ends, (21-) 27-43 (-45) (7.5-) 9.5-13 (-16.5) m. The teleomorph was absent. A voucher specimen (collected from Seattle) was deposited with the Mycological Herbarium at Washington State University (WSP 70310).


     
 

Fig. 1. Foliar symptoms of powdery mildew of Nandina domestica caused by Microsphaera berberidis.

 

Fig. 2. Appressorium formed by Microsphaera berberidis on Nandina domestica.

 

     
 

Fig. 3. Conidiophore of Microsphaera berberidis (by Differential Interference Contrast microscopy).

 

Fig. 4. Conidia of Microsphaera berberidis (by brightfield microcopy).

 

Anamorphic features resembled closely those of M. berberidis (1,3,4,5). Braun (1) noted that M. berberidis usually does not form the teleomorph on species of Mahonia in Europe, and the teleomorph has not been found on Mahonia aquifolium (Pursh) Nutt. in western Washington (3). None of the N. domestica specimens examined included the teleomorph. One of the plants studied was sampled repeatedly during different seasons of the year for three years but no evidence of the teleomorph was found. Earlier studies of M. berberidis on N. domestica in Scotland (4) and California (5) also failed to find the teleomorph. The present report follows the application of this name established in those earlier studies although it is recognized that further work, perhaps at the molecular level, will be important in characterizing more fully the fungi to which this name is applied. Owing to recent work on genus-level taxonomy of Erysiphales, Braun and Takamatsu (2) recently suggested resurrecting the binomial Erysiphe berberidis DC for this fungus.

The voucher specimen is from a plant that exhibited conspicuous powdery mildew symptoms for three consecutive years (2000 through 2002). Although the mildewed leaves were unsightly, the plant tolerated the presence of the fungus with no obvious symptoms of decline.


Literature Cited

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. Glawe, D. A. 2003. First Report of Powdery Mildew of Mahonia aquifolium caused by Microsphaera berberidis (Erysiphe berberidis) in North America. Plant Health Progress doi:10.1094/PHP-2003-206-01-HN.

4. Helfer, S. 1995. First report of powdery mildew on Nandina domestica (Berberidaceae) in Edinburgh (UK). Plant Dis. 79:424.

5. Saenz, G. S., Koike, S. T., and Scheck, H. J. 2000. First report of powdery mildew on Nandina domestica (Berberidaceae) in North America. Plant Dis. 84:705.