First Report of Fusarium falciforme Causing Root and Rhizome Rot of Epimedium sagittatum in China.

Epimedium sagittatum (Sieb.et Zucc.) Maxim., a perennial herb, is an important medicinal plant, rich in flavonoids, and widely used in the treatment of sexual dysfunction, rheumatic disease, and cancers (Tan et al. 2016). In July 2022, a disease of root and rhizome was found on E. sagittatum aged 1-8 years in a planting area (266 ha) of Zhumadian City (32°58'12" N, 114°37'48" E), Henan Province, China. The disease incidence per field (660 m2 ) was around 10-15% in six randomly surveyed fields planted with about 10,000 E. sagittatum plants each. Symptoms included leaf yellowing, root and rhizome browning, rotting and necrosis, and eventually the whole plant wilted and died. Fifteen plants with symptoms were sampled to isolate the pathogen. Symptomatic tissues were cut into small pieces of 5×5 mm, surface sterilized with 75% ethanol for 30 s, followed by three rinses with sterile double-distilled water (ddH2 O). The pieces were then surface disinfected with 0.1% HgCl2 for 30 s, rinsed three times with sterile ddH2 O, placed onto potato dextrose agar (PDA) plates and incubated at 28°C in the dark for 5 days. Twelve deferent Fusarium spp. colonies were purified by excising hyphal tip onto PDA for cultivation. Pathogenicity test of all strains was performed. Only isolate GY2 could result in root and rhizome rot of host plant. Colonies of GY2 on PDA had abundant white aerial mycelia with yellow halo. Macroconidia were hyaline, falciform, with a slightly curved apical cell and blunt basal cell, 29.7~45.0 (average 38.3) × 4.5~6.6 (average 5.3) µm (n =50), with 2-3 septa. Microconidia were oval, or reniform, hyaline, 8.4~26.5 (average 16.5) × 2.7~6.0 (average 4.5) µm (n =50), with 0-2 septa. Morphological characteristics of isolate GY2 were consistent with those of the Fusarium solani species complex (FSSC) (Chehri et al. 2015). For molecular identification, a region of the translation elongation factor 1-α (TEF) and RNA polymerase second largest subunit (RPB2) of GY2 were PCR-amplified and sequenced using the primers EF1-728F/986R (Carbone et al. 1999) and RPB2-5f2/7cr (O'Donnell et al. 2010), respectively. The TEF and RPB2 sequences (GenBank accession nos. OR978135.1 and OR978136.1) of GY2 were concatenated for a phylogenetic analysis using the Bayesian method (Zhang et al. 2020). The phylogenetic tree revealed that isolate GY2 clustered with F . falciforme with a credibility value of 99%. Morphological and molecular results support identification of isolate GY2 as F. falciforme . A pathogenicity test was performed on 4-year-old healthy plants grown in pots. Twenty healthy plants were inoculated by pouring a 200 mL conidial suspension (1×106 conidia/mL) around the rhizome. Control plants received 200 mL of sterile ddH2 O. All treatments were maintained in a greenhouse at 25±1°C and 80% relative humidity. The assay was conducted three times. After 20 days, similar symptoms as those in the field were observed on the inoculated plants, whereas controls remained asymptomatic. Fusarium falciforme was reisolated from the symptomatic plants and showed the same morphological and molecular characteristics as isolate GY2, fulfilling Koch's postulates. Fusarium falciforme was reported to cause root rot of tobacco (Qiu et al. 2023) and industrial hemp (Paugh et al. 2022). However, this is the first report of F. falciforme causing root and rhizome rot of E. sagittatum . Our study will contribute to the development of strategies for the effective management of this disease on E. sagittatum .