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2003 Plant Management Network.
Accepted for publication 14 April 2003. Published 12 May 2003.


First Report of Powdery Mildew of Magnolia Caused by Microsphaera magnifica (Erysiphe magnifica) in the Pacific Northwest


Dean A. Glawe, Plant Pathologist, 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. 2003. First Report of powdery mildew of Magnolia caused by Microsphaera magnifica (Erysiphe magnifica) in the Pacific Northwest. Online. Plant Health Progress doi:10.1094/PHP-2003-0512-02-HN.


Magnolia liliiflora Desrousseaux in Lamarck (orthographic variant: M. liliiflora), a species thought to have originated in China (3), is used as a landscape plant in North America. In August 2002, Microsphaera magnifica U. Braun was collected from three plants of M. liliiflora in the Magnolia collection at the Washington Park Arboretum, University of Washington, Seattle. This report documents for the first time a powdery mildew disease of a Magnolia species in the Pacific Northwest, and the first finding of M. magnifica in the western United States.

Conspicuous signs of the disease were effuse to dense, white patches of mycelium (Fig. 1) on infected leaves. By late September, infected plants were largely defoliated. Mycelia were found to include appendaged ascocarps and conidiogenous structures typical of a species of Microsphaera. Characteristics of the fungus were as follows: Mycelium was amphigenous, primarily on adaxial side of leaf surface; colonies were effuse to dense, forming conspicuous patches that often coalesced, and were generally white to grayish to brown. Anamorph features included conidiophores that were straight with cylindric foot-cells. Conidia (Fig. 2) usually were borne singly, although they occasionally adhereded in chains of 2 to 3 spores and were cylindric with flattened to slightly convex ends, collapsing, with roughened to reticulate surfaces roughened to reticulate, and were (24-) 26.5-31.5 (-32.5) (12-) 14-15.5 (-16.5) m. Teleomorph features included ascocarps (Fig. 3) that were scattered, becoming black at maturity, 75 to 156 m in diameter, with dichotomously branched appendages, producing several asci per ascocarp. Asci (Fig. 4) were saccate to sphaeroidal, 47 to 63 40 to 48 m, and each containing 3 to 6 ascospores. Ascospores were ellipsoid-ovoid, subhyaline to pale yellow, and 21 to 27.5 12 to 17 m. A voucher specimen was deposited in the Mycological Herbarium at Washington State University (WSP number 70314).


     
 

Fig. 1. Symptoms of powdery mildew on Magnolia liliiflora.

 

Fig. 2. Conidium of Microsphaera magnifica.

 

 

Fig. 3. Ascocarp and ascospores of Microsphaera magnifica.

 

Fig. 4. Ascocarp and developing asci of Microsphaera magnifica.


Teleomorphic features of the fungus described herein closely resemble those included in Brauns (1) description for M. magnifica. Braun did not include information on the anamorph. Conidial production in examined material was sparse and in rather poor condition, as evinced by the collapsed conidia, compared to the robust appearance of ascocarps and their contents.

The host range of M. magnifica reported by Braun (1) consists of several species of Magnolia, including M. liliiflora, but the geographical distribution described for the fungus included only Japan and mid-Atlantic and southern states of the United States. Farr et al. (4) reported M. magnifica only from M. acuminata (L.) L. in Pennsylvania, but listed additional Magnolia species and U.S. states in the host and geographical range for M. penicillata (Wallr.: Fr.) Lv. In contrast, Braun (1) restricted M. penicillata, morphologically resembling M. magnifica, to species of Alnus. The present report, and information presented by Braun (1), suggest that M. magnifica is a more widespread and important pathogen of Magnolia in North America than is reflected in the North American literature.

Owing to developments in genus-level taxonomy of Erysiphales, Braun and Takamatsu (2) recently proposed transferring this fungus to the genus Erysiphe as E. magnifica (U. Braun) U. Braun and Takamatsu.

The voucher specimen (WSP 70314) is from a plant that, according to Arboretum staff member Dean Powell, exhibited conspicuous powdery mildew symptoms for several consecutive years up to and including the 2002 growing season. The Magnolia collection of the Arboretum includes 34 species. Magnolia liliiflora was the only species on which powdery mildew was observed, suggesting that it may be more susceptible than other species in the collection.


Literature Cited

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

2. 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.

3. Hunt, D., ed. 1998. Magnolias and their allies. Int. Dendrology Soc. and the Magnolia Soc. Sherborne, UK.

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.