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© 2008 Plant Management Network.
Accepted for publication 16 October 2008. Published 12 December 2008.


First Report of Powdery Mildew of Periwinkle Caused by Golovinomyces orontii 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, WA 98195; and Steven T. Koike, Plant Pathology Farm Advisor, University of California Cooperative Extension, Salinas, CA 93901


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


Glawe, D. A., and Koike, S. T. 2008. First report of powdery mildew of periwinkle caused by Golovinomyces orontii in North America. Online. Plant Health Progress doi:10.1094/PHP-2008-1212-03-BR.


Periwinkle (Vinca major L., Apocynaceae) is a trailing, spreading evergreen plant used in landscapes as a groundcover. Beginning in 2005, a powdery mildew was observed on periwinkle in coastal (Monterey Co.) California. As reported herein, the causal agent was determined to be Golovinomyces orontii (Castagne) V.P. Heluta. This appears to be the first record of a powdery mildew species on Vinca spp. in North America.

Fig. 1. Signs of powdery mildew on Vinca major.

 

Signs of the pathogen included effuse patches of white mycelia primarily on adaxial leaf surfaces of older foliage (Fig. 1). Infected leaves developed gray lesions beneath fungal colonies. Mycelia were superficial, forming nipple-shaped appressoria (Fig. 2). Conidiophores formed foot cells (Fig. 3) that measured (38.5-)48.5-80(-90) × 9.5-12 µm, were enlarged slightly toward apical ends, and exhibited bases that frequently were curved to strongly bent. Conidia (Fig. 4) formed in chains, measured (26-)30-37(-39.5) × (13.5-)15-18(-18.5) µm, were hyaline, ovoid to short-cylindrical, and lacked fibrosin bodies. The teleomorph was not observed. A voucher specimen was deposited with the Mycology Herbarium of the Plant Pathology Department of Washington State University (herbarium designation: WSP).

The fungus was determined to be Golovinomyces orontii (Castagne) V.P. Heluta on the basis of conidial ontogeny, foot cell and conidial size and morphology, shape of appressorium, and host. Braun (2) listed two species of powdery mildews on Vinca spp., G. orontii and Leveillula taurica (Lév.) G. Arnaud. Farr et al. (3) listed no Erysiphales on Vinca spp. in North America, but listed reports of species referable to G. orontii, L. taurica, or O. vincae in current systems of classification (1,2) on Vinca species in Europe, Korea, and North Africa. The present fungus was distinguished easily from L. taurica which forms dimorphic conidia and internal mycelia. Bolay (1) reported two powdery mildew species occurring on Vinca species in Switzerland, G. orontii and Oidium vincae Bolay. The latter species formed lobed appressoria and conidiophores with single conidia, suggesting it likely is the anamorph of an Erysiphe species (1). The present report appears to be the first to document G. orontii on Vinca major in North America.

The disease was found on periwinkle in three of eight surveyed landscapes and in one of five commercial nurseries surveyed. In each case, incidence was limited to a small number of plants. Golovinomyces orontii is thought to be either a single species with broad host range, or a complex of morphologically similar species (1,2). The discovery of G. orontii on V. major in North America suggests this host may be significant in the epidemiology of diseases caused by G. orontii on other host plants in North America. On V. major the primary effect of the fungus seems to be the unsightly signs of the fungus and the foliar lesions associated with infections.


     
 

Fig. 2. Golovinomyces orontii appressorium formed on Vinca major. Scale bar = 15 mm.

 

Fig. 3. Golovinomyces orontii conidiophore formed on Vinca major, with chain of developing conidia and curved foot cell (arrow). Scale bar = 25 mm.

 

 

Fig. 4. Golovinomyces orontii conidia formed on Vinca major. Scale bar = 25 mm.

 

Literature Cited

1. Bolay, A. 2005. Les Oïdiums de Suisse (Erysiphacées). Cryptogam. Helvet. 20:1-176.

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

3. Farr, D. F., Rossman, A. Y., Palm, M. E., and McCray, E. B. 2008. Fungal Databases. Online. Systematic Mycology and Microbiology Laboratory, USDA-ARS, Washinton, DC.