Curvularia lunata Causes a Leaf Spot on Carpetgrass (Axonopus compressus) in China

Carpetgrass (Axonopus compressus [Swartz] Beauv.) is a perennial, warm-season turfgrass adapted to temperate regions. Because of its fine texture and natural tolerance to high temperature, shade, and drought stresses, carpetgrass is widely used in water and soil conservation situations and public green lawns in southern China. During 2015, a field survey conducted in college and park lawns of Zhanjiang, Guangdong Province, revealed the occurrence of an unknown disease on A. compressus in spring and autumn. Initial symptoms appeared as 2 to 4 mm reddish-brown circular spots on the leaves, subsequently increasing in size and coalescing to form 5 to 10 mm oblong lesions. Affected tissue turned brown, advancing to gray as tissues shriveled. Typical symptoms appeared as reddish-brown, circular or oblong lesions with chlorotic centers on leaves. Symptomatic leaf blade tissues (3 × 3 mm) were aseptically separated and surface-disinfested by soaking leaf pieces in 2.5% sodium hypochlorite for 1 min, rinsed in sterile, deionized water twice for 30 s, and placed onto potato dextrose agar (PDA) amended with 0.01% gentamicin sulfate. A dematiaceous hyphomycete with dark brown-to-black fungal colonies was consistently isolated from the diseased samples. Conidiophores were brown, septate, sympodial or unbranched, and geniculate at the apical region with dark brown scars. Conidia were dark brown and cymbiform with 3 to 4 cells, the central cell enlarged resulting in a curved shape, ranging in size from 19.5 to 30.0 × 8.5 to 13.0 μm (mean 22.5 × 10.5 μm, n = 50). These characteristics are consistent with Curvularia lunata (Wakker) Boedijn (Manamgoda et al. 2012). DNA was extracted from two isolates (ZW4-1 and ZW4-2) and the ribosomal internal transcribed spacer (ITS) region and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) were amplified using the primers ITS1 and ITS4 (White et al. 1990), gpd1 and gpd2 (Berbee et al. 1999), respectively. The ITS (accession nos. KX685659 and KX685658) and GAPDH (KX885226 and KX885227) sequences were submitted to GenBank. BLASTn analyses showed the sequences shared 99% similarity with published ITS (JX256429 and JX256430) and GAPHD (JX276441 and JX276442) sequences of C. lunata ex-types, respectively. To confirm pathogenicity, isolates ZW4-1 and ZW4-2 were used to inoculate on A. compressus planted in 10-cm pots by spraying 20 ml conidial suspension (1 × 106 conidia/ml) with a high-pressure sprayer. Control pots were sprayed with distilled water alone. To maintain high humidity, all plots was covered with a plastic bag and maintained in a growth chamber at 28°C with a 12-h photoperiod. Foliar lesions developed on plants 1 week post inoculation, similar to those observed on naturally infected plants. No symptoms were observed on control plants. C. lunata was reisolated from the symptomatic leaves, confirming Koch’s postulates. To the best of our knowledge, this is the first report of leaf spot caused by C. lunata on A. compressu in China. © The American Phytopathological Society.