First Report of Ustilago cynodontis Causing Smut of Cynodon dactylon in Washington State, United States

Abstract

Bermudagrass (Cynodon dactylon) is an important warm-season perennial turf and forage grass that is typically grown in warm, tropical and subtropical climates. Smutted inflorescences of bermudagrass were observed and collected in Benton County, Washington, United States, in October of 2012 in an unmanaged, naturalized area located near the banks of the Columbia River and adjacent to large expanses of managed turf containing bermudagrass. The climate in this area is favorable to bermudagrass due to the relatively mild winters and hot, dry summers that usually occur in this region. The infected plants occurred in patches alongside healthy plants and several disease foci were observed along a 100-m transect of non-contiguous bermudagrass. The disease was severe wherever it occurred. Diseased inflorescences were covered with black-brown teliospores, distorted, and frequently failed to fully emerge and develop. Teliospores (n = 80) were irregularly globose to subglobose, 5.3 to 7.0 × 4.5 to 6.2 μm (mean 6.4 × 5.9 μm) and 6.2 to 8.8 × 5.3 to 7.0 μm (mean 7.0 × 6.5 μm), with a smooth wall approximately 1 μm thick, and were consistent with previous descriptions of Ustilago cynodontis teliospores (1,3). Teliospores germinated within 24 h when plated on 0.2% malt agar at 16°C and produced 4-celled basidia in a 3+1 arrangement, also consistent with U. cynodontis (3). Basidia gave rise to lateral and terminal, ovoid to long ellipsoidal basidiospores. Basidiospores budded or germinated by hyphae from which lateral or terminal aerial sporidia developed as previously described (3,4). DNA was extracted from sporidia of three single-spored isolates grown in malt extract broth. Complete nucleotide sequences of the 5.8S ribosomal RNA coding region and partial sequences of the internal transcribed spacer (ITS) regions 1 and 2 were obtained from the three isolates using ITS1 and ITS4 primers. The corresponding regions of the three aligned sequences (GenBank Accession Nos. KC920742 to KC920744) were identical and exhibited 99 to 100% identity with U. cynodontis strains previously deposited in GenBank (HM143013, AY740168, AF038825, and AY345000). Representative specimens were deposited in the WSU Mycological Herbarium as WSP 72345 to WSP 72348. This is the first report of U. cynodontis causing smut on bermudagrass in Washington State and represents the northernmost record of this fungus in North America (2). The occurrence of U. cynodontis in Washington State suggests that the pathogen may exist in other hot and dry areas of northwestern North America where bermudagrass is found associated with turf in recreational, landscape, or natural settings. References: (1) S. D. Brook. Trans. R. Soc. N. Z. 84:643, 1957. (2) D. F. Farr and A. Y. Rossman. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Online. Retrieved from http://nt.ars-grin.gov/fungaldatabases , April 18, 2013. (3) C. T. Ingold. Trans. Br. Mycol. Soc. 83:251, 1984. (4) C. T. Ingold. Trans. Br. Mycol. Soc. 89:471, 1987.