First report of leaf spot caused by Curvularia verruculosa on Cynodon sp. in Hubei, China

Curvularia leaf spot affects many species of grasses worldwide and is commonly caused by Curvularia eragrostidis, C. geniculata, C. intermedia, C. inaequalis, C. lunata, C. pallescens, C. protuberata or C. trifolii (Smith et al., 1989). Weng et al. (1997) found that the most frequent disease of warm season grasses in southern China was caused by C. lunata and C. affinis has been found on Festuca arundinacea (Huang et al., in press). There have been no other reports of Curvularia leaf spot from central China.

In August 2003, symptoms were observed in Wuhan, China, at a sports field on a Cynodon dactylon x C. transvaalensis hybrid. Yellow-brown spots of varying shape were formed on leaves and sheaths. The spots measured up to 1 cm in diameter. Disease incidence was 5%. Isolations were made on acidified PDA and after 2 days at 25°C, 8 mm diameter cultures with appressed, white mycelium were observed. After 2 more days, the enlarging colonies acquired a greenish cast, which yielded spores of C. verruculosa (Ellis, 1966) with a rough-to-verrucose surface, three septa and an average size of 24.9 µm x 10.3 µm. The two central cells were larger and darker than the terminal cells. Sequencing of the ITS region of ribosomal DNA showed a 99.6% match with a C. verruculosa sequence in GenBank.

Pathogenicity was tested by inoculating field-grown plants. Ten stems, 12 cm long, were placed in petri plates layered with moist tissue paper. Each stem was inoculated with two 5 mm diameter mycelial plugs and the plates were incubated at 25°C, under continuous fluorescent light. The plugs were removed after 48 hr and within 24 hr, small spots appeared. Within 2 days after that, these spots had enlarged up to 1 cm in diameter, turning yellow-brown, with irregular shapes as seen in the field. No spots were seen on uninoculated stems. Isolations from spot margins, away from inoculated areas, yielded spores of C. verruculosa.

This fungus has been reported previously on grass genera such as Buchloe, Chloris, Oryza, Paspalum, Pennisetum, Sorghum, Triticum, Typha and Zea (Sivanesan, 1987), but this is the first report on Cynodon. The spores are similar in morphology to those of C. lunata except for the verrucose surface. Past diagnoses of Curvularia leaf spot may have mistakenly identified C. verruculosa as C. lunata.