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© 2006 Plant Management Network.
Accepted for publication 2 March 2006. Published 5 April 2006.


First Report of Powdery Mildew of Coreopsis Species Caused by Golovinomyces cichoracearum in the Pacific Northwest


Dean A. Glawe, Plant Pathologist, Puyallup Research and Extension Center, Washington State University, 7612 Pioneer Way East, Puyallup 98371-4998; Gary G. Grove, Associate Plant Pathologist / Extension Plant Pathologist, and Mark Nelson, Research Tech Supervisor, Irrigated Agriculture Research and Extension Center, Washington State University, Prosser 99350-8694


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


Glawe, D. A., Grove, G. G., and Nelson, M. 2006. First report of powdery mildew of Coreopsis species caused by Golovinomyces cichoracearum in the Pacific Northwest. Online. Plant Health Progress doi:10.1094/PHP-2006-0405-01-BR.


The genus Coreopsis (Asteraceae) includes various species of perennials and annuals grown in landscapes throughout North America. Powdery mildew diseases caused by several species of Erysiphales are recorded from Coreopsis species in the USA and Canada (2), but Sphaerotheca macularis (Wall.: Fr.) Lind is the only species reported previously on Coreopsis species in the Pacific Northwest (2). During the summer of 2005 we encountered a previously unreported powdery mildew disease of Coreopsis verticillata L. (whorled tickseed) ‘Zagreb’ and Coreopsis auriculata L. (lobed tickseed) ‘Nana’ in central Washington and determined the causal agent to be Golovinomyces cichoracearum (DC.) VP Gelyuta. This report documents the occurrence of G. cichoracearum on Coreopsis species in the Pacific Northwest, and describes diagnostic features of the disease and causal agent.

Disease signs (Fig. 1) included whitish accumulations of conidiophores and conidia typical of powdery mildew. Hyphae were superficial, produced nipple-shaped appressoria, conidiophores (Fig. 2) with foot cells measuring 23.0-52.5 × 10.5-13.5 µm, and chains of conidia. Conidia were hyaline, short-cylindrical to ovoid, lacked fibrosin bodies, and measured 26.5-40.5 × 12.5-18 µm. The teleomorph included sphaeroidal chasmothecia (Fig. 3) measuring 125-220 µm with mycelioid appendages, and multiple short-stipitate asci (Fig. 4) measuring 49.0-58.0 × 29.5-43.5 µm. Ascospores were subhyaline to pale yellow, ellipsoid-ovoid, two per ascus, and measured 24.5-31.5 × 16.0-21.0 µm.


     
 

Fig. 1. Powdery mildew signs caused by G. cichoracearum on C. auriculata.

 

Fig. 2. G. cichoracearum conidiophores.

 

     
 

Fig. 3. G. cichoracearum chasmothecia.

 

Fig. 4. G. cichoracearum asci.

 

Golovinomyces cichoracearum has been reported (as Erysiphe cichoracearum DC) from Coreopsis species in Europe and New Zealand, as well as from California, Illinois, Maryland, Minnesota, New York, and Wisconsin (2). None of those records included the host species documented in the present study. The only powdery mildew fungus reported previously from Coreopsis in the Pacific Northwest is S. macularis on an unidentified Coreopsis species in Washington (2). It is unclear which fungus was the subject of that record since S. macularis is regarded as specific to Humulus species by Braun (1). Sphaerotheca species exhibit fibrosin bodies and chasmothecia with single asci and thus can be distinguished readily from Golovinomyces species, which lack fibrosin bodies and produce chasmothecia with multiple asci (1).

The diseased plants grew in a commercial field for cuttings used in propagation. Disease incidence was evaluated October 20, 2005. Determining disease incidence was complicated by production practices including removal of cuttings from the field and foliar applications of fungicides. In two plots of C. verticillata ‘Zagreb,’ 84% and 100% of plants exhibited signs of the disease.

The discovery of the teleomorph suggests that it may overwinter to produce primary inoculum on Coreopsis species in central Washington. Golovinomyces cichoracearum occurs on a wide range of Asteraceae (1), so infected Coreopsis species might serve as a source of primary inoculum for other Asteraceae in the region.

Although not observed in the present study, Leveillula taurica (Lév.) G. Arnaud also occurs on Coreopsis species in the USSR (1) and occurs on Gaillardia (Asteraceae) in Washington (3). That fungus and Golovinomyces orontii (Castagne) V.P. Gelyuta (in the past confused with G. cichoracearum [1]) co-infect potato (Solanum tuberosum L.) plants in Washington (4). Diagnosticians should be aware that L. taurica and G. cichoracearum might also co-infect Coreopsis species in the Pacific Northwest.


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. Glawe, D. A., Grove, G. G., and Nelson, M. 2006. First report of powdery mildew of Gaillardia × grandiflora (blanket flower) caused by Leveillula taurica in North America. Online. Plant Health Progress doi:10.1094/PHP-2006-0112-01-BR.

4. Glawe, D. A., du Toit, L. J., and Pelter, G. Q. 2004. First report of powdery mildew on potato caused by Leveillula taurica in North America. Online. Plant Health Progress doi:10.1094/PHP-2004-1214-01-HN.