Occurrence of Exserohilum rostratum Causing Leaf Spot on Cenchrus fungigraminus in China

Cenchrus fungigraminus (giant JUNCAO) is a forage, mushroom substrate and bioenergy feedstock with key economic and ecological roles in sustainable agriculture (Zheng et al. 2023). Leaf spots were observed on C. fungigraminus in Yancheng Jiangsu Province (33°2′23.0928″N, 120°41′25.58″E), China in October 2025. Disease incidence reached 65% in 100 plants. Early symptoms appeared as dark brown to black necrotic spots with distinct chlorotic halos. Later, lesions developed grayish centers, coalesced, causing severe blight and plant death. Symptomatic leaf segments (5 × 5 mm) were surface sterilized (75% ethanol 1 min, 1% NaClO 30 s), rinsed four times with sterile distilled water and cultured on potato dextrose agar (PDA) at 28 ℃ and 80% relative humidity for 5 to 10 days (Tembo et al. 2024). Pure isolates (PGY1-PGY4) were obtained by single-hyphal-tip purification, and PGY (representative) was selected for characterization. Circular colonies reached 9 cm in diameter with grayish-black center, grayish-white edge, and dense aerial mycelium after 8 days at 28 ℃. Conidiophores are apically geniculate at the top, with a slightly swollen apex where conidia are attached, and conidia have a truncate basal cell closely attached to the hilum, clavate or fusiform, brown to dark olive-brown (28.86-72.27) μm × (11.45-15.83) μm, and 4-8 septa. Conidiophores were dark brown, septate, unbranched, single or in clusters of 2-6, measuring 4-10 μm in width and 120-310 μm in length. These morphological characteristics align with those of Exserohilum species (Wei et al. 2024). Molecular identification was carried out based on the ITS (White et al. 1990), LSU(Vilgalys et al.1990), GAPDH and TEF1 genes. The sequences were deposited in GenBank (NCBI) under accession numbers PX754901 (ITS), PX754903 (LSU), PZ293715 (GAPDH) and PZ303596 (TEF1). BLAST analysis showed that ITS and LSU sequences had the highest similarity to E. gedarefense, whereas GAPDH and TEF1 sequences showed the highest similarity to E. rostratum. E. gedarefense is treated as conspecific with E. rostratum, and the causal agent is herein identified under the accepted name E. rostratum (Hernández-Restrepo et al. 2018). Phylogenetic analysis clustered the isolates within the E. rostratum clade with 100% bootstrap support. To fulfill Koch’s postulates, C. fungigraminus plants were inoculated with E. rostratum mycelial plugs (5 mm diameter) and plants were maintained under conditions mimicking natural infection (28 ℃, >85% RH). Small dark brown lesions appeared in 3 days inoculation, and typical chlorotic-halo lessions developed by 15 days, matching field symptoms. whereas control plants remained symptomless and yielded no fungal growth upon isolation (Fig. S1M-P). The experiment was biologically replicated three times with consistent results. E. rostratum was consistently reisolated from symptomatic tissues and confirmed via morphological and molecular analyses. Morphological characteristics and molecular diagnostic assays confirmed the pathogen as E. rostratum, which were reported on economically important crops, including Zea mays (Aggarwal et al. 2025) and Calathea orbifolia (Wang et al. 2025). This is the first documented report of E. rostratum infecting C. fungigraminus in China, which will expand the host range of E. rostratum and update the geographic distribution records of this pathogen.