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First Report of Nigrospora Leaf Blight on Elephant Grass Caused by Nigrospora sphaerica in China

Han, Y. Z., Fan, Z. W., Wu, C. F., Li, M. Y., Zhou, D. D.
Plant disease 2019 v.103 no.10 pp. 2681
C4 plants, Cenchrus purpureus, DNA, DNA primers, Nigrospora, air drying, biomass, color, conidia, conidiophores, culture media, ethanol, foliar diseases, forage, fuel production, fungi, genes, hosts, humidity, inoculation methods, internal transcribed spacers, leaf blight, leaves, mycelium, pathogenicity, pathogens, perennials, phylogeny, polymerase chain reaction, seedlings, sodium hypochlorite, subtropics, surveys, tubulin, China
Elephant grass (Cenchrus purpureus Schumach., syn. Pennisetum purpureum Schumach.) is a perennial C4 plant and widely grown across the tropical and subtropical regions of the world. It is cultivated primarily for forage and biofuel production owing to its superior yield of biomass and broad adaptation (Negawo et al. 2018). In September 2018, during our survey in the field in Chongqing, a distinct blight symptom with unknown etiology was observed on leaves of elephant grass. The initial symptoms were frequently observed on the leaf margins and apices, and the color turned red to brown. As the disease progressed, the leaves evolved into severely blighted. This disease causes damage to leaves of all ages and is severe in young leaves. To identify the etiology of this disease, the pieces (5 mm diameter) of symptomatic leaves were surface sterilized using 75% ethanol for 30 s and 0.5% NaClO for 2 to 3 min, rinsed three times in sterile distilled water, air dried, and then plated on potato dextrose agar. The colonies of pathogen grew rapidly and reached 9-cm diameter in 5 days at 25°C. The fungal colonies were white to light yellow, floccose, with regular circular margin. The mycelia were smooth, hyaline, septate, branched, and 2 to 7 μm diameter. Conidiophores were flexuous or straight, hyaline to pale brown. Single-celled conidia were black, globose or subglobose, with diameter around 11 to 16 μm. Genomic DNA was extracted from a representative isolate PPNS1 using a Fungal DNA Kit (GBCBIO, Guangzhou, China), and the universal internal transcribed spacer (ITS) region and partial β-tubulin (TUB2) gene were amplified with primers ITS1/4 and Bt-2a/2b, respectively (Wang et al. 2017). By BLASTn, DNA sequences from ITS and TUB2 showed 100% nucleotide similarity with those from Nigrospora sphaerica (GenBank accession nos. MF380852.1 and KY019618.1). Homology was also confirmed by a phylogenetic tree constructed by MEGA7. The representative sequences were deposited in GenBank (accession nos. MK571184 and MK575866). Based on morphology and nucleotide homology, the associated fungus was demonstrated to be N. sphaerica. According to Koch’s postulates, pathogenicity tests were conducted on four- to five-leaf elephant grass seedlings through both wound inoculation and nonwound inoculation methods. Plants were kept at 28°C with 80% humidity and observed for symptoms every day (Cui et al. 2018). After 10 to 15 days, inoculated leaves developed blight symptoms similar to those observed in the field, and no symptoms were observed on the control leaves. The pathogen was repeatedly isolated from lesions, and its identity was confirmed by morphological characteristics. Thus, N. sphaerica should be responsible for the Nigrospora blight we observed on the elephant grass. N. sphaerica has been reported as a causal agent of foliar disease on a wide range of hosts worldwide. However, to our best knowledge, this is the first report of Nigrospora leaf blight caused by N. sphaerica on elephant grass in China. This disease reduces yield and quality of the leaves. Future research will focus on the management of this disease.