First Report of <i>Fusarium verticillioides</i> Causing Stem Blight of <i>Sinopodophyllum hexandrum</i> in China

The Chinese medicinal herb "Taoerqi" is scientifically classified as Sinopodophyllum hexandrum (Royle) Ying (formerly Podophyllum hexandrum), belonging to the family Berberidaceae (Liu et al. 2021), possesses effective anti-cancer functions (Liu et al. 2015). In December 2024, during cultivation of S. hexandrum in a 100 m² greenhouse at Lanzhou (36°10'N, 103°72'E), approximately 10% of plants exhibited severe disease symptoms. Initially, the leaves exhibited chlorosis and irregular dark brown necrotic lesions, accompanied by stems constriction. Subsequently, the roots exhibited brown discoloration and rot. In severe cases, the entire plant wilted and died. To isolate the pathogen, symptomatic root tissues were excised from five plants, surface-disinfected in sequence with 1% NaClO (sodium hypochlorite) for 1 min and 75% ethanol for 30 s, then rinsed three times with sterile water and placed onto potato dextrose agar (PDA) medium, supplemented with streptomycin sulfate (50 µg/mL) to inhibit bacteria growth. After a 7-day incubation at 25°C in the dark, a consistent fungal isolate was obtained from the diseased tissues by single-spore isolation. Colonies on PDA produced abundant aerial mycelia that were initially white, gradually turning pinkish to violaceous. Conidiophores were sparsely branched, mostly terminating with verticillate phialides. Microconidia were oval or ellipsoidal, measuring 2.9 to 14.9 × 1.3 to 3.4 μm (n = 50). Macroconidia were slender, relatively straight to moderately curved, and falcate, measuring 33.6 to 59.1 × 2.3 to 4.7 μm, with 3 to 5 septa (n = 50). Based on these morphological characteristics, the strain was tentatively identified as Fusarium verticillioides (Gerlach et al. 1982). The translation elongation factor 1-alpha gene (tef1)(O’Donnell et al. 1998), the internal transcribed spacer (ITS), the RNA polymerase II largest subunit (rpb1), and the RNA polymerase II second largest subunit (rpb2) regions of the isolate were sequenced (O’Donnell et al. 2022). The obtained sequences were deposited in GenBank (PV593989, PQ812600, PV593987, PV593988). BLAST analysis revealed that the TEF-1α, ITS, RPB1 and RPB2 regions showed 100% identity (925/925 bp, 533/533 bp, 1,794/1,794 bp, and 944/944 bp, respectively) with F. verticillioides. A multi-locus phylogenetic tree constructed using maximum likelihood in MEGA X (Hall 2013) placed TEQ-LZ in a clade with F. verticillioides. Pathogenicity assays were conducted by soil drenching with 5 mL of conidial suspension (10⁶ conidia/mL) around the roots of six healthy potted seedlings (3 months old) with intact root systems (Zhou et al. 2024), while the control group was treated with sterilized water. The plants were then placed in the greenhouse at 15°C for incubation. After 15 days, typical symptoms identical to those initially observed appeared on the leaves, stems, and roots of all inoculated plants. Approximately 28% of the plants ultimately succumbed to the disease, while the control group remained healthy. Morphological examination and sequence analysis confirmed that the re-isolated fungus was identical to isolate TEQ-LZ, fulfilling Koch’s postulates. This entire experiment was repeated three times with similar results. This is the first report of S. hexandrum stem blight caused by F. verticillioides in China. This finding is crucial for the conservation of S. hexandrum germplasm resources, and advancing research on the disease mechanism.