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© 2010 Plant Management Network.
Accepted for publication 16 March 2010. Published 28 April 2010.


First Report of Leaf Smut of Gaillardia × grandiflora Caused by Entyloma gaillardianum in North America


Dean A. Glawe and Tess Barlow, Department of Plant Pathology, Washington State University and School of Forest Resources, Box 352100, University of Washington, Seattle, WA 98195; and Steven T. Koike, University of California Cooperative Extension, Salinas, CA 93901


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


Glawe, D. A., and Barlow, T., and Koike, S. T. 2010. First report of leaf smut of Gaillardia × grandiflora caused by Entyloma gaillardianum in North America. Online. Plant Health Progress doi:10.1094/PHP-2010-0428-01-BR.


Fig. 1. Symptoms of leaf smut of Gaillardia × grandiflora.

 

In the summer of 2009, a leaf spot disease occurred on 100% of about five thousand plants of Gaillardia × grandiflora cv. Goblin in a commercial nursery in coastal California (Monterey Co.). Nearly all of the affected plants were unsalable, resulting in a loss of approximately $20,000 (retail value). Diseased plants developed adaxial spots on leaves that first were light green, later turned bright yellow, and eventually became necrotic. Spots were generally round, sometimes vein-delimited, 0.5-1.0 cm in diameter (Fig. 1) and included sori of a smut fungus. Disease was most severe on older leaves where spots coalesced and entire leaves senesced prematurely. Sori contained teliospores that were subspheroidal, very pale green to brown, and (10.5-)11-14.5(-16) µm in diameter (Fig. 2). Teliospore walls were smooth, with one or two layers, and (0.5-)1-2.5 µm thick (Fig. 3). Groups of conidiophores emerged from stomata in lesions (Fig. 4). The size, shape, and color of teliospores and the production of conidiophore fascicles matched the description of E. gaillardianum Vánky on Gaillardia species (3).


   
 

Fig. 2. Teliospores formed within host tissue. Scale bar = 25 µm.

 

 

Fig. 3. Teliospore with two-layered walls (arrow). Scale bar = 10 µm.

 

Fig. 4. Fascicle of conidiophores emerging through stoma, and conidia (arrow). Scale bar = 25 µm.


DNA was extracted from sori and the ITS region amplified as described previously (4). The resulting 735 bp amplicon sequence was deposited with GenBank (accession no. GU117108). It was compared with ITS regions from Entyloma species represented in GenBank including: AY081037 and AY854968 from E. gaillardianum Vánky, AY081046 from E. polysporum (Peck) Farl., AY854961 and AY081023 from E. calendulae (Oudem.) de Bary, and AY081026 and AY854966 from E. compositarum Farl. Alignment of these sequences revealed a common region of 648 bp. Comparison of the sequence we determined with those from GenBank revealed similarities (BLASTN, NCBI 2.2.1.5) of 100% and 99% to the E. gaillardianum sequences, 96% to the E. polysporum sequence, 95% and 94% to the E. calendulae sequences, and 94% similarity to the E. compositarum sequence.

Inoculum was prepared by using a bio-homogenizer to macerate the lesions; the mixture was passed through a sieve (no. 14; Tyler equivalent 12 mesh) to remove larger pieces of leaf. The resulting filtrate (1 × 104 spores/ml) was sprayed onto healthy plants. Plants were incubated at 100% RH for 24 h and then kept in a greenhouse. After 14 days, leaf smut developed on inoculated plants and the same pathogen was observed; plants inoculated with water remained healthy.

The causal agent was determined to be Entyloma gaillardianum based on morphological features, host, and ITS region. This species has not been reported previously from this host in North America. Farr et al. (2) listed several other Entyloma species on Gaillardia, but Vánky (5) excluded them from this host genus. Entyloma polysporum was reported on Gaillardia × grandiflora in Virginia (3). However, Vánky (5) noted that the taxonomy of Entyloma species on Asteraceae is complex, and recent work (1) employing sequence data to complement morphological and host data has helped clarify the species occurring on Asteraceae.

It is likely that the presence of the conidial state and the use of overhead sprinkler irrigation contributed to the high incidence and severity of the disease. A voucher specimen was deposited with the Mycology Herbarium, Department of Plant Pathology, Washington State University.


Literature Cited

1. Begerow, D., Lutz, M., and Oberwinkler, F. 2002. Implications of molecular characters for the phylogeny of the genus Entyloma. Mycol. Res. 106:1392-1399.

2. Farr, D. F., Rossman, A. Y., Palm, M. E., and McCray, E. B. 2010. Fungal Databases. Online. Systematic Mycology and Microbiology Laboratory, USDA-ARS, Washinton, DC.

3. Hong, C. X., and Banko, T. J. 2003. First report on white smut of Gaillardia × grandiflora caused by Entyloma polysporum in Virginia. Plant Dis. 87:313.

4. Koike, S. T., Glawe, D. A., and Barlow, T. 2010. First report of leaf smut of tomatillo caused by Entyloma australe. Online. Plant Health Progress doi:10.1094/PHP-2010-0216-01-BR.

5. Vánky, K. 1994. European Smut Fungi. Gustav Fischer Verlag, Stuttgart, Germany.