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© 2003 Plant Management Network.
Accepted for publication 6 November 2003. Published 10 December 2003.


First Report of Powdery Mildew of Ligustrum japonicum (Japanese Privet) Caused by Microsphaera syringae (Erysiphe syringae) in North America


Jennifer S. Falacy, Irrigated Agriculture Research and Extension Center, Washington State University, Prosser 99350-8694; and Dean A. Glawe, Puyallup Research and Extension Center, Washington State University, 7612 Pioneer Way East, Puyallup 98371-4998


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


Falacy, J. S., and Glawe, D. A. 2003. First report of powdery mildew of Ligustrum japonicum (Japanese privet) caused by Microsphaera syringae (Erysiphe syringae) in North America. Online. Plant Health Progress doi:10.1094/PHP-2003-1210-01-HN.


The woody shrub Ligustrum japonicum Thunb. (Japanese privet) is used widely as a landscape plant. The only published report (4) of powdery mildew on this host in North America was based on an anamorphic fungus in Louisiana regarded as a possible species of Microsphaera. The Plant Clinic at Oregon State University houses an unpublished record, dated August 30, 1961, of a powdery mildew on this host in Portland, Multnomah County, Oregon (Jay Pscheidt, personal communication); that fungus was recorded as Microsphaera alni but no voucher specimen or morphological description exists. In August 2002, powdery mildew was collected by Master Gardener Marilyn Tilbury from L. japonicum in Seattle, King County, Washington. The authors determined the causal agent to be Microsphaera syringae (Schw.) Magn. The present report documents for the first time the occurrence of M. syringae on L. japonicum in North America, and presents information on the taxonomy and identification of this fungus.

Signs of the fungus included white mycelium consisting of hyphae, conidiophores bearing single conidia, and brown to black ascocarps. Distinguishing characteristics included lobed appressoria (Fig. 1); ascocarps (85-) 90-113 (-116) µm with dichotomously branched appendages (Fig. 2), short-stipitate asci (Fig. 3) 50-60 (-64 ) × 27-42 (-45) µm each with 4 to 8 oval to phaseoliform ascospores 18-22 (-23) × 10-11  (-12) µm; conidiophores with short cylindrical foot cells and cylindrical conidia (Fig. 4) (26-) 27-35 (-41) × (11-) 12-14 (-15) µm. A voucher specimen (WSP 70743) was deposited with the Mycological Herbarium, Department of Plant Pathology, Washington State University.


     
 

Fig. 1. Appressorium of Microsphaera syringae formed on Ligustrum japonicum.

 

Fig. 2. Ascocarp appendages of Microsphaera syringae formed on Ligustrum japonicum.

 

     
 

Fig. 3. Asci with ascospores formed by Microsphaera syringae on Ligustrum japonicum.

 

Fig. 4. Conidium of Microsphaera syringae formed on Ligustrum japonicum.

 

Morphology of appressoria, conidiophores, conidia, ascocarps, ascocarp appendages, asci, and ascospores, as well as the host genus, fit the description for M. syringae provided by Braun (1). Farr et al. (3) listed Microsphaera penicillata (Wall.: Fr.) Lév. on Ligustrum amurense Carriére, L. vulgare L., and Ligustrum sp. They (3) listed an unidentified Microsphaera species on L. japonicum, citing Holcomb’s (4) report as the source for the record. Braun (1), however, determined that M. penicillata occurs only on Alnus spp. He included M. alni (Wallr.) Wint. (the name in the Oregon State University Plant Clinic records) as a synonym of M. penicillata. Braun (1) reported M. syringae to be widespread on species of Oleaceae in North America. We frequently find M. syringae on Syringa spp. (lilac) in the Pacific Northwest, where in the past it has been identified as M. penicillata. Although we are following Braun’s use of M. syringae in applying it to the fungus described herein, the morphological similarity of this fungus to M. penicillata suggests that studies on host ranges and molecular data would be useful in refining the taxonomy of these species. Braun and Takamatsu (2) suggested synonymizing Microsphaera with Erysiphe, based on ITS sequence data. If this proposal becomes accepted, the name applied to this fungus will be Erysiphe syringae Schw. (2).

The collection of this fungus in Seattle on L. japonicum, and possible findings of it on this host in Portland and Louisiana, suggest that M. syringae may be broadly distributed on this host in North America. Further studies on its taxonomy and host and geographical ranges appear warranted.


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. 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.

4. Holcomb, G. E. 1976. Powdery mildew, a new disease of Ligustrum japonicum. Plant Dis. Rep. 60:346-347.