A disease resembling brown ring (Waitea) patch was observed on a ‘Dominant Extreme’ creeping bentgrass (Agrostis stolonifera) green on a golf course in Maricopa County, Arizona in February 2010. The green was 17 months old and built with 95% sand and 5% peat moss. The superintendent reported seeing yellow rings, 12 to 16 cm in diameter, on several greens as early as 3 months postinstallation; the yellow rings developed into brown, necrotic rings. Symptoms started in the cool, cloudy, and moist conditions of December (5.0 to 6.7°C) and became persistent into the spring. Symptoms on the samples appeared to be yellowing of leaves and stems with the development of a dark, water-soaked appearance of the whole plant on older affected portions. The samples were incubated in a moist chamber at 22 to 25°C for 24 h. Foliar mycelium developed on the symptomatic leaves, and upon microscopic examination, the mycelium appeared to have the characteristics of Rhizoctonia spp.; i.e., a right-angled branching pattern, constriction of the hyphal branch near its point of origin, and the presence of a septum near the point of origin. The pathogen was recovered from chlorotic tissue by plating the symptomatic tissue on one-quarter-strength acidified potato dextrose agar (9.90 g of PDA and 11.26 g of granulated agar [Fisher, Lenexa, KS] and 600 ml of lactic acid [Sigma, St. Louis, MO] per liter of water) and incubating at ~27°C in light. A Rhizoctonia-like pathogen emerged from the tissue within 48 h and was tentatively identified as Waitea circinata var. circinata based on colony and bulbil morphology after 10 days of incubation (3). The recovered isolate was used for DNA extraction and subsequent amplification and sequencing of the rDNA internally transcribed spacer (ITS) region using ITS1F and ITS4 primers (2). The recovered sequence (HM807352) was compared with the National Center for Biotechnology Information (NCBI) nucleic acid database and was found to show 100% similarity to W. circinata var. circinata (FJ755879). To confirm pathogenicity, the isolate was used to fulfill Koch's postulates. The isolate was grown on autoclaved sand and corn meal (250 g of sand and 50 g of corn meal) for 4 weeks to produce inoculum. Eight grams of colonized sand and corn meal was broadcast on 4-week-old creeping bentgrass seedlings (‘Penncross’) planted in a 90:10 peat moss/sand mixture in 10-cm-diameter pots. There were three replications and the experiment was repeated twice. Negative controls consisted of plants inoculated with sand and corn meal only. Pots were maintained at 28 to 33°C in the greenhouse with ambient light. Within 4 days of inoculation, the plants showed chlorosis and necrosis, while noninoculated plants showed no symptoms. The pathogen was successfully reisolated from several plants from each replication using the method described above. This pathogen has been known to cause disease on annual and rough bluegrass (1,2) in the United States, but not confirmed as a pathogen on creeping bentgrass here. To our knowledge, this is the first report of brown ring patch on creeping bentgrass in Arizona.
References: (1) C. M. Chen et al. Plant Dis. 91:1687, 2007. (2) K. de la Cerda et al. Plant Dis. 91:791, 2007. (3) T. Toda et al. Plant Dis. 89:536, 2005.