First Report of a Leaf Blight Caused by Pyricularia pennisetigena on Cenchrus pauciflorus in China

Abstract

Cenchrus pauciflorus Benth., an annual herbaceous plant in the Gramineae family, is a noxious invasive weed in China. In 2016, an unknown leaf blight was observed on C. pauciflorus in Zhangwu county, Liaoning province, China. Initial symptoms appeared as light-brown pinpoints mostly at the leaf apex, which subsequently enlarged along the veins and became oval or elongated, scattered, medium brown, with a dark brown border, greyish necrotic centers mostly, and occasionally distinct yellow halos. Finally, the lesions coalesced, and the leaves became desiccated and brittle. Small pieces from symptomatic leaves were surface disinfested with 75% ethanol and 1% sodium hypochlorite for 1 min, rinsed three times with sterile distilled water, and cultured on potato dextrose agar (PDA) at 28°C. The same fungus was recovered from 85% of the 20 isolates. A pure culture was obtained by single spores of a representative isolate. For morphological characterization, cultures were grown on autoclaved barley seed under a 12-h photoperiod at 28°C and examined after 1 to 3 weeks for sporulation. Colony diameter and macroscopic features were recorded after 1 week of incubation on PDA at 28°C in the dark. Conidia were pale brown, pyriform to obclavate, smooth, two-septate, measured 22.1 to 30.6 × 8.3 to 10.2 μm (mean 24.4 × 9.5 μm), truncate, and protruding of hilum. Conidiophores were brown, single, straight or curved, smooth, multiseptate, and measured 46.3 to 146.8 × 2.9 to 5.7 μm (mean 92.4 × 4.5 μm). The colonies on PDA were light brown with a gray center and white rim, 53 mm in diameter after 1 wk. To confirm pathogenicity, a spore suspension (10⁵ conidia/ml) prepared from autoclaved barley seed was sprayed onto 10 healthy plants of C. pauciflorus, and 10 healthy plants were treated with sterile distilled water as a control. Both treatments were placed at high relative humidity (approximately 95%) for 24 h and then transferred the greenhouse at 25 to 28°C and about 75% relative humidity under natural daylight. Typical spots appeared on all the inoculated leaves after 8 to 10 days and were similar to those originally observed on plants under natural conditions, whereas the control plants remained asymptomatic. The same fungus was reisolated from the inoculated leaves and reidentified. For molecular analysis, the internal transcribed spacers (ITS), partial large subunit (LSU), and partial RNA polymerase II large subunit gene (RPB1) were amplified with primers ITS1/V9G, LR5/NL1, and RPB1F/RPB1R, respectively, and sequenced (Klaubauf et al. 2014). The representative sequences (ITS, LSU, and RPB1) were deposited in GenBank (submission IDs MH412637, MH412638, and MH412639). A phylogenetic tree (with the combined data of ITS, LSU, and RPB1) was obtained using MEGA 4.0 with neighbor-joining analysis, showing that the isolates fall in the Pyricularia pennisetigena clade. The fungus isolated from symptomatic tissues was identified as P. pennisetigena on the basis of morphological and cultural characteristics and sequence analysis (Klaubauf et al. 2014). According to previous reports, the pathogen of P. pennisetigena can infect Cenchrus ciliaris in Japan, Cenchrus echinatus in Philippines, Cenchrus echinatus, Echinochloa colona, Triticum aestivum, and Panicum maximum in Brazil, and Pennisetum glaucum in the United States (Borromeo et al. 1993; Kang et al. 1995; Reges et al. 2016). To our knowledge, this is the first report of leaf blight on C. pauciflorus caused by P. pennisetigena in China.