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© 2007 Plant Management Network.
Accepted for publication 11 October 2007. Published 17 December 2007.


First Report of Powdery Mildew of Stachys byzantina (Lamb’s Ear) Caused by Neoerysiphe galeopsidis in North America


Dean A. Glawe, Plant Pathologist, Department of Plant Pathology, Washington State University, and Professor, College of Forest Resources, Box 352100, University of Washington, Seattle 98195; and Steven T. Koike, Plant Pathology Farm Advisor, University of California Cooperative Extension, Salinas 93901


Corresponding author: Dean A. Glawe.  glawe@wsu.edu


Glawe, D. A., and Koike, S. T. 2007. First report of powdery mildew of Stachys byzantina (lamb’s ear) caused by Neoerysiphe galeopsidis in North America. Online. Plant Health Progress doi:10.1094/PHP-2007-1217-01-BR.


The genus Stachys (Lamiaceae) includes both invasive weeds and ornamentals and a number of species are reported hosts of powdery mildew fungi (Erysiphales). The taxonomy of powdery mildew fungi on North American species of Stachys is complicated by application of varied genus and species concepts to these fungi over many decades. In addition, the taxonomy of Stachys species also has undergone changes since some disease reports were made. North American records of Erysiphales on Stachys species in the database of the US National Fungus collection (4) can be interpreted to include the following: Erysiphe cichoracearum DC. [Golovinomyces cichoracearum (DC.) V.P. Heluta] on S. bullata Benth.; Neoerysiphe galeopsidis (DC.) U. Braun on S. chamissonis Benth. var. cooleyae (Heller) G. Mulligan & D. Munro (as both S. ciliata Epling and Stachys cooleyae Heller), S. floridana Shuttlew. ex Benth., S. mexicana Benth., S. palustris L., Stachys pilosa Nutt. var. pilosa (as S. scopulorum Greene), S. tenuifolia Willd., and undetermined Stachys spp.; Sphaerotheca humuli (DC.) Burrill on S. bullata and undetermined Stachys spp.; and Sphaerotheca macularis (Ehrh.) Magnus on S. bullata and S. mexicana.

Fig. 1. Signs of powdery mildew of Stachys byzantina caused by Neoerysiphe galeopsidis.

 

Records of G. cichoracearum on Lamiaceae likely referred to what is now regarded as N. galeopsidis (1,3). Braun’s world monograph of Erysiphales (1) does not include powdery mildews on Stachys spp. referable to Podosphaera, the genus name applied to species formerly classified in Sphaerotheca (3). Previous records of powdery mildews of Stachys species in California included E. cichoracearum and Sphaerotheca humuli on Stachys bullata and Sphaerotheca macularis on Stachys mexicana (4). During the summer of 2007 the authors encountered a previously unrecorded powdery mildew disease on several plants of the perennial ornamental plant Stachys byzantina K. Koch ex Scheele (common names: woolly hedgenettle, woolly betony, and lamb’s ear) growing in a plant bed near a commercial building in Salinas (Monterey Co.), California. This report documents the occurrence of N. galeopsidis on this host in North America.

Disease signs (Fig. 1) included conspicuous white to grayish patches of mycelia on leaves. Mycelia produced lobed appressoria (Fig. 2). Conidiophores (Fig. 3) formed foot cells that were straight, cylindrical, and measured (23-)29-56(-62 ) × 8-11 µm, and produced chains of conidia. Conidia (Fig. 4) lacked fibrosin bodies, were ovoid to cylindrical, hyaline, measured (27-)28-37(-39) × (12-)13-18(-20) µm, and upon germination formed a germ tube on a lateral surface of conidia. The teleomorph was not observed.


 

Fig. 2. Appressorium of Neoerysiphe galeopsidis formed on Stachys byzantina. Scale bar = 15 µm.

 

     
 

Fig. 3. Conidiophore of Neoerysiphe galeopsidis formed on Stachys byzantina. Scale bar = 25 µm.

 

Fig. 4. Conidia of Neoerysiphe galeopsidis formed on Stachys byzantina. Scale bar = 25 µm.

 

Based on morphological features of the anamorph, including the lobed appressoria, catenulate conidia, sizes of foot cells, sizes and shapes of conidia, and the lack of fibrosin bodies, as well as the host genus, the fungus was determined to be N. galeopsidis. Formerly designated Erysiphe galeopsidis DC., this fungus was reported previously from S. byzantina in Denmark, Germany, Poland, Romania, United Kingdom, and the former Czechoslovakia and USSR (2,4). It does not appear to have been reported on this host in North America.

Although it is uncertain whether this disease would contribute to premature death of the host, the conspicuous disease signs detracted significantly from the appearance of the infected plants. Because S. byzantina is a widely grown ornamental species, susceptibility to powdery mildew could be a significant concern to nurserymen, landscapers, and gardeners. The host range of Neoerysiphe galeopsidis includes numerous genera of Lamiaceae (1). Studies on the host range of the strain on S. byzantina would be useful to determine whether this host species could be a possible source of inoculum for powdery mildew of Lamiaceae in North America.


Literature Cited

1. Braun, U. 1987. A monograph of the Erysiphales (powdery mildews). Beih. Nova Hedwigia 89:1-700.

2. Braun, U. 1995. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Stuttgart.

3. Braun, U., Cook, R. T. A., Inman, A. J., and Shin, H.-D. 2002. The taxonomy of powdery mildew fungi. Pages 13-55 in: The Powdery Mildews: A Comprehensive Treatise. R. R. Bélanger, W. R. Bushnell, A. J. Dik, and T. L. W. Carver, eds. The American Phytopathological Society, St. Paul, MN.

4. Farr, D. F., Rossman, A. Y., Palm, M. E., and McCray, E. B. Fungal Databases. Online. Systematic Botany & Mycology Laboratory, USDA-ARS, Washinton, DC.