First Report of Brown Ring Patch Caused by Waitea circinata var. circinata on Poa annua in Wisconsin and Minnesota

In summer of 2008, two turfgrass samples were submitted to the Turfgrass Diagnostic Lab at the University of Wisconsin-Madison. The samples were from golf courses in Beaver Dam, WI on 12 June and Minneapolis, MN on 14 July. Both samples were collected from 40-year-old native soil putting greens mowed at 3.2 mm that had received annual sand topdressing since 1992. The putting greens were a mixture of approximately 75% annual bluegrass (Poa annua L.) and 25% creeping bentgrass (Agrostis stolonifera L.) Stand symptoms observed in the field were bright yellow, sunken rings that were approximately 5 cm thick and 15 to 35 cm in diameter. Some rings were incomplete, giving a scalloped appearance. Affected plants were severely chlorotic and lacked any discrete lesions or spots. Symptoms were more prominent on annual bluegrass than creeping bentgrass. Upon incubation of samples at room temperature in a moist chamber for 24 h, fungal mycelia with septations and right-angle branching were observed in the foliage and thatch layer. Two isolates were obtained from affected annual bluegrass in each sample. Isolations were performed by washing affected leaves in 0.5% NaOCl solution for 2 min, blotting the tissue dry, and plating the tissue on potato dextrose agar (PDA) amended with chloramphenicol (0.05 g/liter), streptomycin (0.05 g/liter), and tetracycline (0.05 g/liter). After incubation for 2 days at 23°C, isolates were transferred and maintained on PDA. All four isolates had multinucleate hyphae and displayed sclerotial characteristics similar to those reported for Waitea circinata var. circinata (2). Sequencing the ITS1F/ITS4-amplified rDNA internal transcribed spacer (ITS) region confirmed the isolates as W. circinata var. circinata, with ≥99% sequence similarity to published W. circinata var. circinata ITS sequences (GenBank Accession No. FJ755849) (1,2,4). To confirm pathogenicity, isolates were inoculated onto 6-week-old annual bluegrass (True Putt/DW184) grown in 10-cm-diameter pots containing calcined clay (Turface; Profile Products LLC., Buffalo Grove, IL). Two 4-mm-diameter agar plugs for each isolate were removed from the margins of 3-day-old colonies grown on PDA and placed near the soil surface to ensure contact with the lower leaf blades. Each isolate was placed in four separate pots to have four replicated tests per isolate, and four noninfested pots were utilized as negative controls. All pots were placed in moist chambers at 28°C with a 12-h light/dark cycle. Within 4 to 6 days, inoculated plants exhibited severe chlorosis and a minor amount of aerial mycelium was observed. Inoculated plants became necrotic after 15 to 20 days, while the noninoculated plants remained healthy. W. circinata var. circinata was reisolated from inoculated plants and its identity was confirmed by morphological and molecular characteristics. This pathogen was previously reported as a causal agent of brown ring patch of creeping bentgrass in Japan and annual bluegrass in the western United States (2,4). To our knowledge, this is the first report of brown ring patch in Minnesota and Wisconsin. Intensive fungicide practices are needed to control brown ring patch; therefore, this disease could have significant economic impact throughout the Upper Midwest (3). References: (1) C. M. Chen et al. Plant Dis. 93:906, 2009 (2) K. de la Cerda et al. Plant Dis. 91:791, 2007. (3) J. Kaminski and F. Wong. Golf Course Manage. 75(9):98, 2007. (4) T. Toda et al. Plant Dis. 89:536, 2005.