First Report of Fusarium commune Causing Root Rot on Ligusticum chuanxiong in China

Abstract

Ligusticum chuanxiong Hort., the dried rhizome of which is a commonly used herb for its therapeutic purposes in Chinese medicine (Wang et al. 2025). Root rot is a prevalent and devastating disease in the cultivation of L. chuanxiong, with 20–50% incidence in major production areas, leading to significant yield losses. The disease occurs throughout the growing period, with the most severe damage occurring at the seedling stage. Infected plants exhibit brownish lesions inside basal stems and roots, progressive softening and water-soaking of internal tissues, and rhizome decay with a sour odor as the disease progresses. In July 2024, three symptomatic root samples of L. chuanxiong were collected from Anguo, Baoding City, Hebei Province, China (38°22′25″N, 115°21′18″E). Symptomatic roots were rinsed thoroughly with clean water, surface-disinfected by immersing in 5% sodium hypochlorite solution for 2 minutes, followed by three washes with sterile distilled water. The roots were dissected by a sterile scalpel, and tissue pieces of approximately 5 mm were excised from the junction between diseased and healthy areas. These segments were plated on potato dextrose agar (PDA) and incubated at 25°C under dark conditions for 3 days. Emerging hyphal tips growing from the disinfected tissues were transferred to fresh PDA plates, and single-spore isolates were obtained by dilution plating. Six isolates with similar colony morphology were obtained. The colony of the representative isolate initially developed white, floccose-to-cottony aerial mycelia that formed a vigorous, dense mat and pale purple pigments with prolonged incubation. To induce sporulation, the isolate was cultured on carnation leaf agar (CLA) at 25°C under a 12 h light/12 h dark regime for 7 days. Macroconidia were typically falcate, with 3 to 5 septa, and measured 22.8 to 44.9 × 3.8 to 7.2 μm (n=50), and microconidia were ovoid, with 0 to 1 septum, measuring 4.8 to 14.4 × 3.3 to 6.8 μm (n=50). These morphological characteristics are consistent with the description of Fusarium commune (Skovgaard et al. 2003). To identify these isolates, the representative isolate designated FC-1 was selected for molecular identification. Genomic DNA was extracted and three loci were amplified and sequenced: the internal transcribed spacer (ITS) region using primers ITS1/ITS4 (White et al. 1990); the translation elongation factor 1-alpha (TEF-1α) gene using primers EF1/EF2; and the RNA polymerase second largest subunit (RPB2) gene using primers RPB2-5f2/RPB2-7cr (O’Donnell et al. 2010). Forward and reverse sequences were assembled to generate consensus sequences for each locus. The consensus sequences were deposited in GenBank with accession numbers PX487973 (ITS), PX529605 (TEF-1α) and PX529607 (RPB2). BLASTn analysis revealed that the sequences exhibited 100% identity to Fusarium commune. Phylogenetic analysis of the concatenated TEF-1α and RPB2 gene sequences indicated that FC-1 clustered with F. commune. To assess pathogenicity, the isolate was cultured in 100 mL of potato dextrose broth (PDB) at 25°C with constant shaking at 200 rpm for 4 days. Cultures were filtered through 4 layers of sterile cheesecloth to obtain spore suspensions (1×106 spores/mL). Healthy L. chuanxiong plants were selected for whole-plant pathogenicity tests. After washing and surface sterilization, the roots were immersed in spore suspensions for 30 minutes and subsequently potted in sterilized substrate. Control roots were treated with sterile distilled water. The pathogenicity test was conducted with three replicate pots per treatment and repeated three times independently. All plants were incubated at 25°C with 85% relative humidity under a 12 h light/12 h dark regime in a growth chamber. After 7 days incubation, inoculated plants developed typical symptoms, including aboveground wilting and chlorosis, as well as internal rot of the rhizome, whereas control plants remained asymptomatic. Three independent assays demonstrated the consistent pathogenicity of FC-1 to L. chuanxiong. The pathogen was successfully re-isolated from symptomatic tissues and identified via sequencing as the original inoculum, thereby fulfilling Koch’s postulates. This study represents the first confirmed report of F. commune as the causal agent of root rot in L. chuanxiong, highlighting a novel and significant threat to the sustainable cultivation of this important medicinal plant.