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2010 Plant Management Network.
Accepted for publication 11 November 2009. Published 16 February 2010.


First Report of Leaf Smut of Tomatillo Caused by Entyloma australe


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


Corresponding author: Steven T. Koike.  stkoike@ucdavis.edu


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.


 

Fig. 1. Disease symptoms of leaf smut of tomatillo.

In 2009, an unidentified disease was observed on commercial tomatillo (Physalis philadelphica Lam.) grown in greenhouses in central coastal California (San Benito Co.). Disease incidence was well over 50%; disease severity could be high, with some plants having all foliage, except for the youngest new leaves, turning yellow and withering. Affected leaves developed adaxial spots that first were light green, later turned bright yellow, and eventually became necrotic. Spots were generally round, sometimes vein-delimited when occurring near major leaf veins, and 0.5-1.0 cm in diameter (Fig. 1). Corresponding abaxial sides of spots were white with conidiophores emerging from stomata in fascicles (Fig. 2). Mature conidia were not seen. Disease was most severe on older leaves, where spots coalesced and resulted in senescence and drying of entire leaves. Sori contained teliospores that were subspheroidal to angular, transparent to pale green, and (9-)9.5-15.5(-15.5) m in diameter (Fig. 3). Teliospore walls were smooth, consisted of one or two layers, and were (0.5-)1-2.5 m thick (Fig. 4).


 

Fig. 2. Conidiophores forming conidia (arrow). Scale bar = 25 m.

 

 

Fig. 3. Teliospores formed within host tissue. Scale bar = 25 m.

 

Fig. 4. Teliospores, some with two-layered walls (arrow). Scale bar = 10 m.


Approximately 1 mm³ of sorus material was excised, DNA extracted, and the ITS region amplified using protocols described previously (4) except that primer P3 (5) was substituted for ITS4. The resulting amplicon was 619 bp. Compared to a Genbank ITS sequence for Entyloma australe (gi 27371349), sequences differed by one base substitution and one indel (>99% similarity). Additional Entyloma species reported on other genera in the Solanaceae include E. petuniae Speg., E. nierenbergiae Lagerh., and E. browalliae Syd. (2). Of these, only E. browalliae is represented in GenBank, by ITS sequences (gi 61387339 and gi 27371351). The 588 bp region common to both of those sequences is identical. Comparison of those sequences with the sequence we generated revealed that the E. browalliae sequences differed from the E. australe sequences in 2-3 indels and 4-5 base changes and were consistent with a phylogenetic study that maintained E. australe and E. browalliae as distinct species (1). The ITS sequence was deposited with GenBank and a voucher specimen deposited with the Mycology Herbarium of the Plant Pathology Department at Washington State University.

Pathogenicity was confirmed by inoculating plants with inoculum prepared by grinding diseased leaves, straining out leaf material, and spraying the resulting teliospore suspension (1 × 104 spores/ml) onto healthy tomatillo plants. Plants were incubated in a humidity chamber for 24 hours and then kept in a greenhouse. After 14 days, leaf smut disease developed on inoculated plants and the same pathogen was observed in diseased tissue; plants treated with water did not develop the disease.

The causal agent was identified as Entyloma australe Speg. based on host and on pathogen morphology and ITS region sequence. The size, shape, and color of teliospores and the production of fascicles of conidiophores fit the descriptions for E. australe (3). This appears to be the only Entyloma species occurring on Physalis (2,3). Fischer (3) included 15 named species of Physalis in the host range for E. australe, as well as species of solanaceous genera Lycopersicon, Quincula, and Solanum. This report appears to be the first record of E. australe on P. philadelphica.


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. Fischer, G. W. 1953. Manual of the North American Smut Fungi. Ronald Press Co., New York, NY.

4. Glawe, D. A., Dugan, F. M., Liu, Y., and Rogers, J. D. 2005. First record and characterization of a powdery mildew (Erysiphales) on a member of the Juncaginaceae: Leveillula taurica on Triglochin maritima. Mycol. Progress 4:291-298.

5. Takamatsu, S., and Kano, Y. 2001. PCR primers useful for nucleotide sequencing of rDNA of the powdery mildew fungi. Mycoscience 42:135-139.