First Report of Brown Ring Patch Caused by Waitea circinata var. circinata on Agrostis stolonifera and Poa pratensis in China.

Abstract

Brown ring patch, caused by Waitea circinata var. circinata, is a recently described disease of turf grass (1,2). The disease was first reported in Japan in 2005 (2) and then in the United States (1). In late May to early September 2011, large yellow rings (20 to 30 cm in diameter) were observed on creeping bentgrass (Agrostis stolonifera) and Kentucky bluegrass (Poa pratensis) growing at the Qinghe Bay golf course, Beijing, China. Leaf blades turned from yellow to brown as the disease developed, and eventually died. The disease incidence was estimated at 20 to 30%. The rings became continuous on creeping bentgrass and Kentucky bluegrass in several putting greens. The same symptom was observed on the lawn of China Agricultural University. Symptomatic leaves were collected and incubated in high humidity at 25°C until mycelia developed. The leaves were then disinfested in 1% NaClO for 1 min, rinsed with sterile water three times, and placed on potato dextrose agar (PDA). Four isolates were obtained, including one isolate from the lawn of China Agricultural University (cau-1), and three from Qinghe Bay golf course (qhw-1, qhw-2, and qhw-3). The colonies that formed on PDA changed from white to orange over time, and minute orange to brown sclerotia (approx. 2 to 3 mm in diameter) formed after 2 weeks at 25°C. These characteristics were similar to W. circinata var. circinata (1,2). DNA was extracted from each isolate using a CTAB extraction method (3) and the internal transcribed spacer (ITS) regions were amplified with the ITS1/ITS4 universal primers. The ITS sequences of the isolated fungi (Accession Nos. JQ964235 and JQ964236) had 99 to 100% homology with the sequences of W. circinata in GenBank (Accession Nos. EU591763 and HQ207169). Pathogen inocula were prepared by inoculating autoclaved oat grains with strains qhw-1 and cau-1 respectively, followed by 4 days of incubation at 25°C. Each inoculum was placed in five spots in a uniform arrangement (5 g grain inoculum per spot) on soil in a 40 × 60 cm tray, followed by sowing bluegrass seed. In another experiment, 4-week-old bentgrass was transplanted into soil infested with 5 g grain inoculum in the middle of a 20-cm diameter pot (non-colonized grain was used as a control). There were five replicates for each isolate. Plants were then incubated in a growth chamber at 26°C and high relative humidity (>90%). After 5 to 6 days, the grass in the inoculated pots and trays began to turn yellow, and then became chlorotic and necrotic as the disease developed. Orange sclerotia were observed on the bluegrass leaves by the eighth day, and all the bentgrass turned chlorotic by the tenth day. After 2 weeks, brown ring patches formed in the trays with inoculated bluegrass. Waitea circinata var. circinata was reisolated from all inoculated plants and confirmed by morphological observation and the ITS sequences analysis as described above, while no symptoms were observed on the control plants and no isolate was obtained from them. To our knowledge, this is the first report of W. circinata var. circinata infecting turf grass in China.