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2012. Plant Management Network. This article is in the public domain.
Accepted for publication 7 January 2012. Published 27 February 2012.


First Report of Erysiphe knautiae (Erysiphales) on Lomelosia caucasica (Caucasian Pincushion Flower) in North America


Frank M. Dugan, USDA-ARS Western Regional Plant Introduction Station, Washington State University, Pullman, WA 99163-6402


Corresponding author: Frank M. Dugan.  fdugan@wsu.edu


Dugan, F. M. 2012. First report of Erysiphe knautiae (Erysiphales) on Lomelosia caucasica (Caucasian pincushion flower) in North America. Online. Plant Health Progress doi:10.1094/PHP-2012-0227-01-BR.


Lomelosia caucasica (M. Bieb.) Greuter & Burdet (synonym Scabiosa caucasica Bieb., Caucasian pincushion flower) is a perennial ornamental plant native to Turkey and the Caucasus region. Traditionally classified in the Dipsacaceae, Lomelosia and Scabiosa are distinct clades in the Scabioseae s. str., separate from Dipsaceae, Knautieae, and other tribes (2). On 22 September 2011, the author collected a specimen at Manito Park Perennial Garden, Spokane, WA. The specimen displayed faintly diffuse powdery mildew infection, primarily on adaxial leaf surfaces, with colonies approximately 5-10 mm in diameter or confluent. Because Scabiosa is amongst the genera in the USDA-ARS National Plant Germplasm System collection at Pullman, the specimen was examined.

The garden label designated the plant as Scabiosa caucasica, pincushion flower, variety ‘House Hybrid.’ The plant keyed to S. caucasica in a comprehensive key that included species later assigned to Lomelosia (4). The powdery mildew had conidiophores ranging ca. 88-140(-175) μm long, with foot cells ca. 33-70(-104) × 7-10 μm and with typically 1-2 cells above the foot cell (Fig. 1). Conidia were elliptical to elongate ovoid to sub-cylindrical, usually 33-46 × 15.5-19.5 μm, lacking fibrosin bodies, and borne individually or in false chains (Fig. 2). Appressoria were lobed (Fig. 3). The teleomorph was not observed. The specimen is deposited as WSP 72104.


 

Fig. 1. Conidiophore with foot cell (arrow) and conidia of Erysiphe knautiae. Differential interference contrast. Bar = 40 μm.

 

     
 

Fig. 2. Fresh conidium of E. knautiae, illustrating absence of fibrosin bodies. Differential interference contrast. Bar = 15 μm.

 

Fig. 3. Germinating conidium with germ tube ending in lobed appressorium. Differential interference contrast. Bar = 10 μm.

 

The powdery mildew keyed to Erysiphe knautiae Druby (1). The other powdery mildews on Scabiosa (incl. Lomelosia) are Leveillula taurica (LÚv.) Arnaud (with strongly dimorphic conidia), and Sphaerotheca dipsacearum (Tul. & Tul.) Junell, (with conidia in true chains and with fibrosin bodies) (1). The specimen conformed to the description of E. knautiae (1) regarding usual variation in conidial length and width, but differed by slightly diminished ranges for maxima and minima. About 80% of the foot cells of the specimen also conformed to the description, but a minority of foot cells were longer than described. GenBank records are lacking for E. knautiae, although some records for Oidium sp., intriguing if not conclusive, are mentioned below. Identification was performed on the basis of host and morphology.

Print or online references typically note powdery mildew of pincushion flower (sometimes specifying host species), and occasionally make management recommendations, sometimes including fungicides. No such references were located documenting species or even generic identity of powdery mildew (other than ‘Oidium,’ which may denote anamorphs of Erysiphe, Golovinomyces, Neoerysiphe, Podosphaera, or other genera). GenBank includes a record for Oidium sp. on Scabiosa columbaria L. from New York, having high sequence similarity to an Oidium sp. from Knautia arvensis (L.) J.M. Coult. in the Netherlands; the original report assigned the Netherlands Oidium to E. knautiae on unspecified criteria, and summarized sequence similarities of the Oidium isolates to Oidium on other hosts (3). The host-fungus record documented herein appears novel for North America. This or other species of powdery mildew are recorded on L. caucasica in Europe, Armenia, or the former USSR (3). Erysiphe knautiae has been reported from Washington State on S. columbaria L., and “Erysiphe polygoni” (probably not E. polygoni DC, restricted to the Polygonaceae) has been reported on Scabiosa sp. and S. atropurpurea L. in the United States (1,3).


Literature Cited

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

2. Carlson, S. E., Mayer, V., and Donoghue, M. J. 2009. Phylogenetic relationships, taxonomy, and morphological evolution in Dipsacaceae (Dipsacales) inferred by DNA sequence data. Taxon 58:1075-1091.

3. Farr, D. F., and Rossman, A. Y. 2012. Fungal Databases. Online. Systematic Mycology and Microbiology Laboratory, USDA-ARS, Washinton, DC.

4. Matthews, V. A. 1972. Scabiosa L. Pages 602-621 in: Flora of Turkey and the East Aegean Islands, Vol. 4. P. H. Davis, ed. Edinburgh Univ. Press, Edinburgh, Scotland.