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© 2004 Plant Management Network.
Accepted for publication 24 February 2004. Published 16 March 2004.


First Report of Powdery Mildew of Akebia quinata Caused by Microsphaera akebiae (Erysiphe akebiae) in North America


Dean A. Glawe, Plant Pathologist, and Jenny R. Glass, Extension Coordinator, 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., and Glass, J. R. 2003. First report of powdery mildew of Akebia quinata caused by Microsphaera akebiae (Erysiphe akebiae) in North America. Online. Plant Health Progress doi:10.1094/PHP-2004-0316-01-HN.


Akebia quinata (Houtt.) Decne. (chocolate-vine, five-leaf akebia) originated in Asia and is grown as a perennial ornamental vine in North America (1). During investigations of the Erysiphales in the Pacific Northwest, five collections were made from A. quinata plants in western Washington exhibiting symptoms of powdery mildew. The causal agent was determined to be Microsphaera akebiae Sawada. This report documents the presence of this fungus in North America for the first time, describes and illustrates the appearance of this fungus and the disease it causes, and reviews aspects of the taxonomy of the fungus and features useful in identification.

Signs of the disease included effuse regions of white mycelium on adaxial leaf surfaces (Fig. 1) which sometimes developed reddish-brown or black discoloration in the epidermis under the mycelium (Fig. 2). The fungus formed hyphae with lobed appressoria (Fig. 3). Conidiophores exhibited cylindrical foot cells and bore single conidia. Conidia were hyaline, with faint striations that became more pronounced when conidia dried and collapsed (Fig. 4) and measured (22-)30-42.5(-45.5) ◊ (12-)12.5-15 Ķm. A voucher specimen (WSP 70742) made August 13, 2003 from Seattle, King County, WA was deposited with the Mycological Herbarium of the Plant Pathology Department at Washington State University. Four additional specimens were studied: two from Seattle collected in 2003, one collected in 2003 in LaConner, Skagit County, WA, and another from Lakewood, Pierce County, WA made in 2002. The powdery mildews in each specimen were indistinguishable from one another.


 

Fig. 1. Symptoms of powdery mildew on leaves of Akebia quinata caused by Microsphaera akebiae.

 

Fig. 2. Close-up view of leaf surface showing reddish-brown discoloration of leaf surface on severely diseased leaf.


     
 

Fig. 3. Lobed appressorium of Microsphaera akebiae formed on Akebia quinata.

 

Fig. 4. Conidium of Microsphaera akebiae showing cell wall striations (photographed with bright-field microscopy).

 

Morphological features of the fungus fit those described for M. akebiae which has been reported from China, Japan, and Korea, but not North America (2). Braun and Takamatsu (3) recently proposed transferring this species to the genus Erysiphe and designated it as Erysiphe akebiae (Sawada) U. Braun & S. Takamatsu.

The plant from which the voucher collection was made exhibited symptoms of powdery mildew for more than one growing season without causing any apparent effect on plant vigor. The mildewed leaves detract from the appearance of the foliage, an unwelcome situation for growers who select this plant partly because of the attractive foliage. Further research would be necessary to determine if powdery mildew causes substantial damage to this host species.

Establishing the presence of the fungus at one site during 2002 and four sites in 2003 suggests that M. akebiae might be well-established in western Washington. Braunís monograph (2) lists only Akebia quinata and A. trifoliata Koidz. as hosts for M. akebiae, the only powdery mildew fungus reported from Akebia. Presumably the fungus was transported to Washington on live Akebia plants. Farr et al. (4) list only two fungi (species of Diplodia and Phoma) from A. quinata, and they do not include any fungi on other host species in the family Lardizabalaceae. It appears that plant pathologists and mycologists have paid little attention to fungi on Lardizabalaceae in North America. Research on Akebia species in other regions of the continent will be necessary to clarify more fully the distribution of M. akebiae.


Literature Cited

1. Brenzel, K. N., ed. 1995. Sunset Western Garden Book. Sunset Publishing Corporation, Menlo Park.

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

3. 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.

4. Farr, D. F., Bills, G. F. Chamuris, G. P., and Rossman, A. Y. 1989. Fungi on plants and plant products in the United States. American Phytopathological Society, St. Paul, MN.