First Report of Take-All Root Rot Caused by Gaeumannomyces graminis on Hybrid Bermudagrass in China.

Abstract

Take-all root rot caused by Gaeumannomyces graminis (Sacc.) Arx & Olivier is a destructive disease of hybrid bermudagrass (Cynodon dactylon × C. transvaalensis Burtt-Davy) (Elliott 1991; Stephens et al. 2020). In April 2018, multiple circular to irregular patches (10 to 200 cm in diameter) were evident on 'Tifway419' bermudagrass fairway of Wohu golf course (Huangshan city, Anhui province). Patches were found at five of the 18 fairways and showed a decrease in stand density. Individual plants in patches exhibited off-color to white foliage, dark and necrotic lesions were frequently observed on roots and associated stolons. Ectotrophic runner hyphae and lobed hyphopodia are ubiquitous on the surface of necrotic roots. Two diseased samples were collected from each patch by a soil corer (10 cm in diameter), and a total of ten patches were sampled across the five symptomatic fairways. Symptomatic roots or stolons were cut into 2 to 3 cm length and surface disinfested for 3 min in 0.6% sodium hypochlorite solution. The sterilized tissues were rinsed, air dried on sterile filter paper for 5 min and placed on potato dextrose agar (PDA) amended with 50 mg L-1 each of ampicillin, streptomycin sulfate and tetracycline. Plates were incubated in the dark at 20°C for 5 days, and similar colonies were consistently recovered from 85% of the symptomatic tissues. After hyphae purification, a total of 20 fungal isolates were obtained with morphology similar to G. graminis (Hernández-Restrepo et al. 2016). DNA was extracted and amplified with primers ITS5/ITS4 (White et al. 1990). PCR products were sequenced (deposited as MZ889119 and MZ889120 in GenBank), and showed 99.43 to 99.81% homology when compared with a known G. graminis isolate (accession no. KX306505). To complete Koch's postulates, healthy Tifway419 hybrid bermudagrass was grown in 5 × 20 cm Cone-Tainers containing a sand and Pindstrup substrate (Pindstrup Mosebrug, Pindstrup, Denmark) mixture (1:1, V/V) nine weeks after transplanting from the experimental field of the Institute of Botany, Jiangsu Province and Chinese Academy of Sciences. Five sterile oat seeds infested with G. graminis were inserted 5 cm below the soil surface in the root zone of Tifway419. Cone-Tainers inoculated with five noninfested sterile oat seeds served as controls, and each treatment was replicate 3 times. All Cone-Tainers were transferred into a growth chamber with a 12-h day/night cycle at 25/20°C and 95% relative humidity. They were covered with plastic bags for the first week, and watered once daily to encourage disease development. Hybrid bermudagrass inoculated with G. graminis decreased in plant density and turfgrass quality, black and necrotic roots covered with lobed hyphopodia were observed eight weeks after inoculation, no symptoms were present on the roots and above-ground of noninfested control plants. G. graminis was consistently reisolated from symptomatic roots and stolons, and confirmed by sequencing the ITS region as mentioned above. To our knowledge, this is the first report of G. graminis causing take-all root rot of hybrid bermudagrass in China, which may influence the management of this important root disease.