First Report of Fusarium solani Causing Root Rot of Atractylodes chinensis in China

Abstract

Atractylodes chinensis (DC.) Koidz is an important medicinal plant in China. In 2024, symptoms of root rot were observed in Hebei Province, China, with disease incidence ranging from 5 to 10% in surveyed fields. Affected plants initially displayed wilting, leaf curling, and gradual brittleness of foliar tissue. Root tissues turned brown and soft, gradually shrinking and hardening, becoming easily breakable and ultimately leading to plant death. To identify the pathogen, small sections were excised from the margins between symptomatic and healthy tissues, surface-sterilized in 75% ethanol for 30 s followed by 0.1% HgCl2 for 1 min, and rinsed three times with sterile distilled water. A fungus was isolated and subcultured on PDA at 25°C in the dark for 5-7 days, colonies exhibited white aerial mycelia with subsurface beige pigmentation. Macroconidia were falcate, typically 5 to 7 septate, with a slight curvature in the midregion, measuring 30.8 to 52 × 4.8 to 6.5 µm (n = 50). Microconidia were oval to reniform and aseptate or with 1 to 2 occasionally 2 septa, measuring 8.9 to 15.2 × 2.8 to 3.5 µm (n = 50). Chlamydospores were abundantly produced within 2-4 weeks on carnation leaf agar (CLA) and the diameter were 5.4 to 8.6 (n = 50). These morphological characteristics were consistent with descriptions of species within the Fusarium solani species complex (Leslie and Summerell 2006). For molecular identification, partial sequences of the translation elongation factor 1-alpha (TEF) and RNA polymerase II second largest subunit (RPB2) genes were amplified using primers EF1/EF2 and RPB2-5F/7cR, respectively, following O'Donnell et al. (2022). Sequences were deposited in GenBank as TEF (PX549679) and RPB2 (PX549683). The obtained TEF (PX549679) and RPB2 (PX549683) sequences showed >99% identity and ≥99% query coverage with reference sequences of Fusarium solani (TEF, PQ862924; and RPB2, MT305173). A phylogenetic tree was constructed using concatenated TEF and RPB2 sequences in MEGA version 11.0.10 (Tamura et al. 2021) with the GTR+G model and 1,000 bootstrap replicates. Maximum Likelihood analysis placed the isolates within the F. solani clade with 99% bootstrap support. Pathogenicity of the representative isolate was confirmed on healthy 1-year-old A. chinensis plants (cultivar: Zhongqin 1). Roots were wounded with a sterile syringe needle (three wounds per root) and inoculated with 10 mL of a conidial suspension (1 × 106 conidia mL-1). Inoculated plants were maintained in a humid chamber at 25 ± 1°C and approximately 85% relative humidity. Control plants were treated with sterile double-distilled water. After 10 days, inoculated plants developed symptoms identical to those observed in the field, and the fungus was consistently reisolated from symptomatic tissues, thus fulfilling Koch's postulates. The experiment was conducted three times, each with 30 plants. Based on symptomatology, morphological characteristics, TEF and RPB2 sequence analysis, and pathogenicity tests, the pathogen was identified as F. solani. F. solani has previously been reported as a pathogen of Astragalus membranaceus var. mongholicus and Gastrodia elata in China (Xu et al. 2024; Chen et al. 2023). To our knowledge, this is the first report of F. solani causing root rot of A. chinensis in China. These findings provide important information on the causal agent of A. chinensis root rot and will support the development of disease management strategies and guide future research.