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© 2005 Plant Management Network.
Accepted for publication 18 October 2005. Published 21 November 2005.


First Report of Powdery Mildew on Corylus avellana caused by Phyllactinia guttata in Washington State


Sierra Hartney, Graduate Research Assistant, Department of Plant Pathology, Washington State University, Pullman 98164; Dean A. Glawe, Plant Pathologist, Puyallup Research and Extension Center, Washington State University, 7612 Pioneer Way East, Puyallup 98371-4998; Frank Dugan, Research Plant Pathologist, USDA-ARS, Pullman WA 99164; and Joseph Ammirati, Professor, Department of Biology, 355325 406 Hitchcock Hall, University of Washington, Seattle 98195-5325


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


Hartney, S., Glawe, D. A., Dugan, F., and Ammirati, J. 2005. First report of powdery mildew on Corylus avellana caused by Phyllactinia guttata in Washington State. Online. Plant Health Progress doi:10.1094/PHP-2005-1121-01-BR.


Contorted hazelnut (Corylus avellana L., Betulaceae) is an ornamental tree introduced to North America from Europe and used for landscaping due to its unusually shaped branches. In the fall of 2004 and 2005, powdery mildew caused by Phyllactinia guttata (Wallr.:Fr.) Lév. was observed on contorted hazelnut (‘contorta’) located on the campus of Washington State University, Pullman, Whitman Co. Powdery mildew also was observed on several C. avellana trees (unknown cultivar) on the campus of the University of Washington, Seattle, King Co. There are previous reports of P. guttata occurring on C. avellana in Europe, Iran, and Canada (2), but within the U.S. P. guttata has been reported on this host only in Oregon (1). This report documents for the first time the occurrence of P. guttata on C. avellana in both eastern and western Washington.

Signs of the disease included white mycelial growth and accompanying chasmothecia on abaxial leaf surfaces. Symptoms included production of chlorotic areas visible on adaxial leaf surfaces. Chasmothecia (Fig. 1) were globose, convex on the ventral side, and nearly plane on the dorsal side; each with a gelatinous mass of penicillate cells (Fig. 2) and acicular appendages. Chasmothecia were (175-) 185-215 (-225) µm in diameter by 100-130 (-145) µm high; appendage length was (360-) 415-495 (-545) µm; penicillate cell bases were 29-48 (-62.5) × (7-) 9-17 (-20) µm and digitate processes were (27-) 32.5-48 (-50.5) × 1.5-3 (-4) µm. Asci (Fig. 3) were short-stipitate, clavate to nearly spindle shaped, 70-85 (-90) × 35-45 µm, and contained two ascospores. Ascospores (Fig. 4) were ellipsoid-ovoid, yellowish-orange, highly guttulate, and (29.5) 32-42 (-42.5) × (17.5-) 19.5-24 (-25) µm. Several conidia resembling those reported for this species (1) were observed but were in poor condition. Voucher specimens were deposited with the Mycological Herbarium (WSP) of the Plant Pathology Department at Washington State University.


     
 

Fig. 1. Chasmothecium of P. guttata produced on C. avellana. Arrow designates gelatinous mass formed by penicillate cells.

 

Fig. 2. Penicillate cell produced by P. guttata viewed with brightfield microscopy.

 

     
 

Fig. 3. Asci and ascospores produced by P. guttata viewed with brightfield microscopy.

 

Fig. 4. Ascospores produced by P. guttata viewed with differential interference contrast microscopy.

 

Phyllactinia guttata attacks a very broad range of deciduous trees (1) but the lectotype consists of material collected from C. avellana (1), the same host observed in the present study. Although too little anamorphic material was seen to characterize it, teleomorphic features, including morphology of chasmothecia, appendages, penicillate cells, asci, and ascospores, match known features for P. guttata (1). Phyllactinia guttata has been reported from other hosts, including Corylus spp., in Washington but not from C. avellana. Phyllactinia corylea (Pers.) P. Karst. also has been applied to fungi occurring on various hosts, including Corylus spp., in the U.S. but it is regarded as a synonym of P. guttata (1).

The fungus did not cause detectable damage to host plants observed in this study. The fungus was observed on one plant in Pullman during the summers of 2004 and 2005. The fungus was observed on the same C. avellana landscape plants in Seattle for many years without being conclusively identified, and the plants showed no sign of significant damage. These observations are consistent with the behavior of this fungus on trees in commercial hazelnut orchards in Oregon where the disease it causes is regarded as not serious enough to warrant control (3,4). Although it is possible that under environments conducive to disease development this pathogen could cause cosmetic damage, the disease appears unlikely to threaten the long-term survival of infected plants.


Literature Cited

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

2. Farr, D. F., Rossman, A. Y., Palm, M. E., and McCray, E. B. 2005. Online. Fungal Databases, Systematic Botany & Mycology Laboratory, ARS, USDA.

3. Pscheidt, J. W., and Ocamb, C. M., eds. 2005. Pacific Northwest Plant Disease Management Handbook. Oregon State Ext. Serv., Corvalis, OR.

4. Teviotdale, B. L., Michailides, T. J., and Pscheidt, J. W. editors. 2002. Compendium of Nut Crop Diseases in Temperate Zones. American Phytopathological Society, St. Paul, MN.