First report of Polygonatum odoratum (Mill.) bud rot caused by Fusarium nirenbergiae in Hunan Province, China

Polygonatum odoratum (Mill.) Druce , a perennial herb in the family Liliaceae, is an economically important medicinal plant widely cultivated in China. (Liu et al. 2024). From May to November 2024, a severe bud rot disease was observed on P. odoratum cv. Xiangyuzhu in Huaihua City, Hunan Province (110.46°E, 26.01°N). Disease incidence reached 30–40% in the main production areas, with yield losses exceeding 20% in severely infested fields. Early symptoms included 2-mm-diameter dark brown spots on the bud, which gradually expanded over time, eventually causing a foul odor and rot of the whole bud. Infected plants often had small rhizomes, many branches, and the overall loss of quality. To clarify the identity of the pathogen,10 symptomatic plants were selected arbitrarily from the production field. After soil on the surface of the infected tissue was washed off with distilled water, tissue segments at the junction of symptomatic and healthy-appearing tissue were excised with a sterile knife. The tissue segments were soaked in 75% ethanol for 30 s, transferred to 5% sodium hypochlorite (NaClO) for 3 min, and then washed three times with sterile water. Water on the surface of the tissue was dried with sterile filter paper, and the segments were then placed on potato dextrose agar (PDA) and incubated in darkness at 25℃ for 5 d. Eight colonies (Y1-Y8) were isolated, all with similar morphological characteristics; further identification confirmed that all were derived from the same fungal strain. Colonies on potato dextrose agar (PDA) were pinkish to purplish, translucent, with radial growth. Macroconidia were falcate, slightly curved, with 3–5 septa, measuring 25.32–45.25 × 2.12–4.87 μm(mean ± SD = 34.6 ± 4.2 × 3.6 ± 0.6 μm). Microconidia were aseptate, oval, 2.69–4.95 × 2.47–4.06 μm (mean ± SD = 3.7 ± 0.5 × 3.2 ± 0.4 μm). Conidiogenous cells were simple, and chlamydospores were observed. The morphology of all isolates was consistent with description of Fusarium nirenbergiae in the Fusarium classification system (Moss and Thrane 2004). Molecular identification was performed using five loci: ITS, Ccam, Tub2, RPB2, and EF‑1α(Zeng et al. 2017). Phylogenetic analysis and multi-locus sequence comparison confirmed that isolate Y1 was conspecific with Fusarium nirenbergiae, as it formed a monophyletic clade with the ex-type strain CBS 840.88 (bootstrap = 99%) and shared high sequence identity (>99.5%) across four core loci. All sequences were deposited in GenBank (accession Nos. ITS: PX745046; Ccam: PX883936; Tub2: PX883939; RPB2: PX883937; EF‑1α: PX883938). Koch 's postulates were tested using a wound inoculation method. Buds of asymptomatic P. odoratum seedlings were surface‑disinfested with 75% ethanol and rinsed three times with sterile water. A 4‑mm‑diameter wound was created on each bud using a sterile needle, and a 4‑mm-diameter mycelial plug of Y1 (5‑day‑old PDA culture) was placed on the wound with mycelium facing the tissue. Control plants were wounded and inoculated with sterile PDA plugs only. Six replicate plants were used per treatment. All plants were incubated at 25 °C, 70% relative humidity, 12 h/12 h light/dark. Symptoms were recorded daily for 7 days（Wei J.,et al. 2026). The re‑isolated fungus was identical to Y1 in morphology and multi-locus sequence, fulfilling Koch’s postulates. Fusarium nirenbergiae can also cause wilt of Acer negundo (Zhao et al., 2020) and Passiflora edulis as well as corm rot disease of Crocus sativus . To our knowledge, this is the first report of bud rot associated with F. nirenbergiae on P. odoratum in China. This finding provides a basis for improving disease management in P. odoratum production.