Characterization of Fusarium redolens associated with Polygonatum cyrtonema Hua root rot disease in Hunan, China

Polygonatum cyrtonema Hua, a perennial herb belonging to the genus Polygonatum in the Asparagaceae family, is widely distributed across provinces such as Hunan, Hubei, and Yunnan, and is known for its various medicinal effects. In 2025, root rot disease was detected in the 33.3-hectare P. cyrtonema plantation on Xuefeng Mountain in Huaihua, Hunan Province. The disease started with the leaves gradually turning yellow and withering. This progressed to root and stem rot, ultimately killing the plant. The incidence rate reached approximately 40%, which has had a significant impact on P. cyrtonema cultivation. To identify the causative pathogen, we randomly collected infected P. cyrtonema tubers for pathogen isolation. Following surface cleaning, samples were sterilized sequentially with 75% ethanol for 90 s and 30% H2O2 for 40 s. Subsequently, sterilized water was used for multiple rinses. The dried samples were cultured on water agar at 28°C for 2–3 days, followed by transfer of the developed mycelia to potato dextrose agar (PDA). Of 35 purified fungal isolates, 24 (68%) were morphologically identified as putative Fusarium, three strains (HJSR1, HJSR3, HJSR4) were selected for further study. For molecular identification purposes, the translation elongation factor 1-a (TEF) and RNA polymerase II β-subunit (RPB2) genes, were amplified and sequenced using primer pairs TEF-F/TEF-R (Nitschke et al. 2009) and RPB2-5F/RPB2-7cR (Reeb et al. 2004), respectively. The obtained sequences were deposited in GenBank under accession numbers: HJSR1 (TEF: PX637278; RPB2: PX637281), HJSR3 (TEF: PX637279; RPB2: PX637282), and HJSR4 (TEF: PX637280; RPB2: PX637283). A phylogenetic analysis was performed using a concatenated tree based on two genes. The analysis revealed that three strains clustered significantly with Fusarium redolens. The fungus grew dense white hyphae on PDA, with flocculent hyphae. Macroconidia were sickle-shaped with 2-3 septa and measured 8.94 to 37.22 × 4.63 to 4.76 μm, while the microconidia were pear-shaped and curved, typically without septa, and measured 6.29 to 13.05 × 2.94 to 3.73 μm. We concluded that the three fungi belong to Fusarium redolens, based on the collective evidence from colony morphology and phylogenetic analyses. To evaluate pathogenicity, definitive tests were performed with appropriate controls. Twelve healthy, uniformly growing Polygonatum plants were selected and placed in a growth chamber maintained at 28℃ and 65% relative humidity. We observed that no symptoms appeared in the plants over several days. In three parallel trials, we treated the experimental group by applying a conidial suspension via root drenching, while the control group acted as a blank control. Disease symptoms, including leaf yellowing and wilting, first appeared on experimental plants at 12 days post-inoculation (Daniel et al. 2011). By day 21, the entire plant had died, while the control plants showed no symptoms and remained healthy. This confirmed that Fusarium redolens is responsible for the root rot disease in Polygonatum. It is known that Fusarium redolens has been reported to cause root rot in ginseng (Fan et al. 2021), stem rot in Polygonatum seedlings (Tang et al. 2021), and root rot in tobacco (X et al. 2023). However, this is the first report of Fusarium redolens causing root rot disease in P. cyrtonema. These findings provide valuable insights for the future control of root rot disease in P. cyrtonema.