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© 2006 Plant Management Network.
Accepted for publication 6 October 2006. Published 27 November 2006.


First Report of Powdery Mildew of Omphalodes cappadocica Caused by Golovinomyces cynoglossi (Erysiphe cynoglossi) 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 91895; and Joseph F. Ammirati, Professor, Department of Biology, Box 351800, University of Washington, Seattle 98195


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


Glawe, D. A., and Ammirati, J. F. 2006. First report of powdery mildew of Omphalodes cappadocica caused by Golovinomyces cynoglossi (Erysiphe cynoglossi) in North America. Online. Plant Health Progress doi:10.1094/PHP-2006-1127-03-BR.


Omphalodes cappadocica DC (Boraginaceae) (common name: Navel Seed) is native to Asia Minor and is grown as an ornamental plant in the USA where it is valued for its bright blue flowers (2). During continuing studies of Erysiphales in the Pacific Northwest, powdery mildew was observed on specimen plants of O. cappadocica growing in a private garden in Seattle, King Co., WA in August 2006. Review of scientific literature revealed no published information on a powdery mildew fungus attacking a species of Omphalodes in North America. This report describes and illustrates powdery mildew of O. cappadocica as well as taxonomically-important features of the causal organism, determined to be Golovinomyces cynoglossi (Wallr.) V. P. Gelyuta.

The disease was found on each of eight plants of O. cappadocica observed during early senescence following anthesis. There were no visible symptoms or damage distinguishable from normal senescence. Signs of the disease (Fig. 1) included effuse to dense patches of white- to grayish-brown mycelia, primarily on adaxial leaf surfaces. The fungus formed superficial hyphae with nipple-shaped appressoria (Fig. 2); conidiophore foot cells that were cylindrical and measured (39.5-)60.5-86(-86.5) ◊ 9.5-12(-13) μm; and conidia that formed chains (Fig. 3) and were ovoid to cylindrical (Fig. 4), lacked fibrosin bodies, and measured (24.5-)28.5-41.5(-44.5) ◊ (8.5-)12.5-20.5(-23) μm. The teleomorph was not observed. A voucher specimen was deposited with the Mycological Herbarium of the Department of Plant Pathology at Washington State University.


     
 

Fig. 1. Signs of powdery mildew of Omphalodes cappadocica.

 

Fig. 2. Appressorium formed by Golovinomyces cynoglossi on Omphalodes cappadocica.

 

     
 

Fig. 3. Conidiophore with chain of conidia formed by Golovinomyces cynoglossi on Omphalodes cappadocica.

 

Fig. 4. Conidia formed by Golovinomyces cynoglossi on Omphalodes cappadocica.

 

Fungal morphological characteristics and host fit Braunís (3,4) descriptions for Erysiphe cynoglossi (Wallr.) U. Braun. That name is regarded as synonymous with Golovinomyces cynoglossi. Braun (3,4) distinguished G. cynoglossi from the morphologically similar E. cichoracearum DC, now known as Golovinomyces cichoracearum (DC.) V.P. Gelyuta. In his (3,4) system, G. cichoracearum restricted to members of the Asteraceae.

Golovinomyces cynoglossi occurs on species of various genera of Boraginaceae (3,4) and recently was found on Myosotis sylvatica Ehrh.: Hoffm. (Boraginaceae) in western Washington State (5). Although previous reports of G. cynoglossi on Omphalodes species are lacking for North America, the fungus is known to occur on O. cappadocica in Asia and Georgia (1), and on Omphalodes linifolia (L.) Moench in Estonia, Germany, Lithuania, and Switzerland (1,4).

Powdery mildew on O. cappadocica is unsightly and a diseased plant would be judged unacceptable by most home owners. However, in this occurrence the disease was observed on plants after the period of flowering and so did not detract from the appearance of the plants when they were showiest. The manifestation of G. cynoglossi during the period following anthesis resembles the disease development observed for powdery mildew of M. sylvatica in Seattle (5), where obvious fungal development also occurred late in the life cycle of the host.

The apparent ability of G. cynoglossi to infect a wide range of Boraginaceae (3,4) suggests that it could pose a threat to growers specializing in ornamental Boraginaceae. Information on host ranges of G. cynoglossi strains, based on cross-inoculation studies, would provide useful information for disease control.


Literature Cited

1. Amano, K. 1986. Host Range and Geographical Distribution of the Powdery Mildew Fungi. Japan Sci. Soc. Press, Tokyo.

2. Armitage, A. A. 1997. Herbaceous Plants: A Treatise on their Identification, Culture, and Garden Attributes. Stipes Publishing, Champaign, IL.

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

4. Braun, U. 1995. The Powdery Mildews of Europe. Gustav Fischer Verlag, Jena.

5. Glawe, D. A. 2004. First report of powdery mildew of Myosotis sylvatica (wood forget-me-not) caused by Golovinomyces cynoglossi (Erysiphe cynoglossi) in Washington State. Online. Plant Health Progress doi:10.1094/PHP-2004-1124-01-HN.