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İ 2009 Plant Management Network.
Accepted for publication 5 June 2009. Published 10 August 2009.


First Report of Podosphaera alpina f. alpina on Tolmiea menziesii in Washington State and British Columbia


Lydia S. Putnicki, College of Forest Resources, Box 352100, University of Washington, Seattle, WA 98195; and Dean A. Glawe, Department of Plant Pathology, Washington State University, Pullman 99164, and College of Forest Resources, Box 352100, University of Washington, Seattle, WA 98195


Corresponding author: Lydia Putnicki.  ltymon@u.washington.edu


Putnicki, L. S., and Glawe, D. A. 2009. First report of Podosphaera alpina f. alpina on Tolmiea menziesii in Washington state and British Columbia. Online. Plant Health Progress doi:10.1094/PHP-2009-0810-01-BR.


Tolmiea menziesii (Pursh) Torr. & A. Gray (Saxifragaceae, piggyback plant) is an understory species typically sold as an ornamental houseplant. Sphaerotheca mors-uvae (Schwein.) Berk. & M. A. Curtis was reported on T. menziesii in Oregon in 1955 (5). That fungus, currently designated Podosphaera mors-uvae (Schwein.) U. Braun & S. Takam. (3), now is regarded as occurring only on Ribes species (Grossulariaceae) (2) so the earlier determination is doubtful. We recently made several collections of T. menzii in Washington and British Columbia with powdery mildew symptoms and determined the causal agent to be Podosphaera alpina f. alpina (U. Braun) U. Braun & S. Takam. This is the first report of this fungus on T. menziesii in Washington and British Columbia.

Four collections of powdery mildew were characterized. Specimens were collected in 2008 from a residential garden in Seattle, King Co., WA; the Washington Park Arboretum, Seattle; and Van Dusen Botanical Garden in Vancouver, BC, Canada. Another specimen was collected in 2004 from a residential garden in Puyallup, Pierce Co., WA. Voucher material was deposited in the Mycology Herbarium, Department of Plant Pathology, Washington State University.

Fig. 1 Nipple-shaped appressorium (arrow) formed by Podosphaera alpina f. alpina. Scale bar = 15 µm.

 

Signs included white colonies on adaxial leaf surfaces. Appressoria (Fig. 1) were nipple-shaped to indistinct. Conidia (Fig. 2) were produced in chains, contained fibrosin bodies, were ovoid to sometimes ellipsoid in shape, and were (23.5-) 29.0-34.0(-41.5) × (12.5-)14.5-19.0 (-23.5) µm. Conidiophore foot cells (Fig. 2) were straight, cylindrical and (63.0-) 64.0-90.0 (-114.0) × (7.0-) 9.0-14.5 (-16.0) µm. Chasmothecia initially were yellowish, black at maturity, and (63.0-) 72.0-95.0 (-121.0) µm in diameter. Chasmothecial appendages (Fig. 3) were mycelioid, variable in length and 0.5 to 6 times the diameter of the ascocarp; peridial cells were (3.5-) 25.0-47.0 (-63.0) µm and irregular in outline. Each chasmothecium contained one sessile ascus (Fig. 4) that was ellipsoid to subglobose and (63.0-) 72.0-95.5 (-121.0) × (62.0-) 70.0-90.0 (-104.5) µm. Each ascus contained six to eight ascospores measuring (12.5-) 14.0-20.0 (-25.0) × (11.0-) 13.0-14.5 (-20.0) µm.


   

Fig. 2. Conidia containing fibrosin bodies (left arrow) and conidiophore (right arrow) formed by Podosphaera alpina f. alpina. Scale bar = 50 µm.

 

 

Fig. 3. Mycelioid chasmothecial appendages formed by Podosphaera alpina f. alpina. Scale bar = 25 µm.

 

Fig. 4. Ascus and ascospores formed by Podosphaera alpina f. alpina. Scale bar = 25 µm.


Based on host and anamorph and teleomorph features, this organism was determined to be Podosphaera alpina f. alpina (1,2). Braun (2) distinguished two forms of P. alpina f. alpina with ascospores ca. 13-22 × 10-16 µm, and f. macrospora U. Braun with ascospores 18-30 × 11-18 µm. Collections in this study fit his concept of f. alpina. Podosphaera astilbicola (Z.Y. Zhao) U. Braun & S. Takam. is another species reported from Saxifragaceae, but it forms considerably smaller chasmothecial peridial cells (2). There are no reports of P. astilbicola from T. menziesii.

Braun (2) listed various saxifragaceous hosts (Heuchera, Saxifraga, Tellima, and Tiarella) and Bolay (1) included Tolmiea in the host range for Switzerland. The US National Fungus Collection (4) holds specimens of P. alpina on Tellima grandifora from Alaska, British Columbia, and California, and on Heuchera sp. from Colorado. The host range suggests that P. alpina f. alpina could have potential to cause economic losses in a greenhouse propagation facility, although to date it has not been reported as a serious pathogen.


Literature Cited

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

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

5. Loring, L. B., and Nicholson, H. 1955. Powdery mildew on Tolmiea menziesii. Plant Dis. Rep. 39:334.